Zuma rear wheel locked after overhaul
 

I recently did an overhaul on my 2002 Yamana Zuma YW50 (49cc 2-stroke), a thing I have never done before. I replaced the v-belt, cleaned up the variator, and replaced some missing springs from my clutch shoes. I also opened up the gear box, removed and then replaced the main drive gear, and replaced the transmission oil with some fresh ATF. I noticed when I was done that my engine had/ still has a small leak between where the exhaust attaches to the cylinder, but it was driving just fine, had much better pick-up, and no more smoke coming from the exhaust. That was about a week ago, and I haven't driven it much more than an few miles since then until today.


Today I took it for its first long drive, about 10 miles round trip. I got to about mile-4 when as I was accelerating through an intersection, the engine died on me. Also, the scooter didn't just coast to a stop, it was like the rear wheel had somehow locked up on me. I could smell hot rubber, but figured this was just the new v-belt getting situated. I opened up the crank case, found nothing wrong. Closed it up again and restarted the machine. Seemed to be fine. Got back on and kept on driving. Around mile 6 it happened again: opening up the throttle began to make the scooter move slower, not faster, and I dropped from around 35mph to less than 5. The engine didn't sound happy. I was able to keep it moving a little while longer (maybe 200 feet), but I knew I was doomed. When I finally came to halt, the rear wheel would not move at all— not like it was stuck by the rear brake shoe, but as though the gears in the gear box were not allowing it to turn. I put it up on the kick stand, and the rear wheel will move just a few degrees in each direction easily. If I put it back on the ground and push it hard, it resists me but it WILL turn. Also, I can hear what sounds like the engine starting up again, though there is no key in the ignition and it is turned off! It's as though the rear wheel is turning the variator and trying to start the machine up.


I ended up parking it along the side of the road and catching an Über home. Tomorrow I will need to go back out there and try to fix it, but I have no idea what could be wrong. I was not able to identify anything actually burned or overly hot around the crank case, but the smell of hot rubber persisted. My v-belt looked just fine when I opened the crank case up at mile 4. But the scooter is stuck now!


Am eager to know if anyone has any ideas what might be wrong! I sure don't!

It sounds like the scooter had a soft seize, from the stall, hot rubber, then started back up description. Soft seize = lean motor. Not good. That can easily be checked by removing the exhaust and looking at the piston bottom. Scrapes on the exhaust side of the piston mean the top end is done. If the piston looks correct, youre ok. You said you did an up-gear? Who pressed the gears? Did they space them correct, with the proper space? Did all the spacer washers go back in the correct location? A friend had a spacer washer on the wrong side and it let a gear shift just enough to lock them up. He was lucky the case didnt get a hole punched in it. Finally, fix the exhaust leak when you check the piston. The exhaust pulls excess heat off the motor and controls back pressure. Running a 2-stroke without one is even worse.

Almost forgot. Who did the belt and related tune-up parts come from? Running a wrong sized belt can really cause serious problems. Why were springs missing from the clutch? I've seen those springs break and cause major damage. It almost sounds like a variator roller shattered, or a v-slide from the back plate on the variator jammed. My friend had a v-slide crack on his Metro and it locked the transmission kinda like youre describing. I had to rescue him with my wifes little pick-up truck. Took us forever to remove the back plate of the variator! Let us know what you find.

Last first
 

Starting with your last question first, I did the repairs to the overhaul myself— I have tried to be my own mechanic for my scooter, and have so far been successful with this: I rebuilt the engine once, have replaced my own front hydraulic break pads, and have replaced both tires myself in the past. The crank case and its contents are new ground for me, though. I had also been trying to adjust the rich/ lean mix of the fuel in an attempt to reduce the smoke from the exhaust— I had been trying to lean it out, since it seemed to be always running too rich. I may very well have ended up running it too lean. Damn. Damn, damn, damn. You are saying that I will be able to see any scrapes on the piston if I remove the exhaust and look up? And that if I find any, I am gonna have to get it towed home to work on it? And will need to replace the cylinder head? Ow. Lets hope this is not it, though according to what you have said, it almost certainly is. It's a haul to get back out there, so may not be able to check until tomorrow, but will certainly be updating you soon.


I am certain the belt is the correct size: I was careful to select a belt that was a direct replacement for the one I had, and I measured it before installing it, I also watched it operate, watched the variator close while the clutch opened, and it seemed to work fine at the time (3 days ago). I don't recall any spacer washers inside the gear box, but myself pressed the drive gear into its casing: I had to freeze it to do this, but once it was frozen good and the gear box cover was hot I used a rubber mallet to smack the drive gear and its bearing into the box cover before replacing the gasket (one I cut myself, and which was not leaking fluid) and closing up the box. The scooter sat for several days following this, with no loss of fluid from around the gear box anywhere, but I am considering draining it and opening it up again anyway to check this.


I won't have my new gasket for the exhaust/ cylinder connection for a few more days, and it sounds like I shouldn't attempt to even start it until that gasket is in place, but if, as you said, there are scratch marks on the piston, will a new gasket here matter much? I will need to replace the piston (I assume) and the cylinder head? Yes? These are nightmare things to have to do, but if they are necessary and if the alternative is to sell it for parts and have no more scooter, than I guess I will have to do them.


But first, I need to get back out there with some tools and have a look. Ugh. Will let you know how I progress, even if it is only misery that lies ahead of me!

Its actually normal to see a bit of smoke on an older/pre-catalytic 2-stroke. Leaning it (carb) out to make the exhaust smoke go away will slowly kill the top end. Thats why I asked you if you had a base setting for the carb.

I always run OEM belts from Yamaha. Only $25 dollars/+ or - $3. There is no accurate way to measure a v-belt, as multiple factors come into play. Trust me, we have experimented enough to know what works and what does major damage when it fails.

Reduction box. There is actually a required "space" when you press the new gear on. I borrow the press at my local machine shop and set it with a feeler gauge. Its a tolerance fit, and if its off (the "space") it grinds the inside of the case, or stresses the big gear-causing bearing failure.

Scooter Swap Shop sells the best exhaust gaskets. We buy them in bulk (I have 10 on hand) because things come loose when youre running 12,000 rpm's at 65mph.

If you do find the piston scraped up on the exhaust side and you decide to replace the top end, find the base settings for the carb before starting it-or the same thing will happen again. I gave away a low miles/mint OEM top end and carb not long ago. Actually, a bunch of Zuma bug-eye stuff. I still have my mint 98 Zuma but its still in pieces. I may also be buying back an old 03 Zuma from my boss if he upgrades to something bigger. If I do, I'll regret giving away all my bug-eye/2-stroke parts.

Good luck!

Response and suggestions for what to do next?
 

Regarding the v-belt: when I say I "measured" it, I mean I verified that the width of the belt was correct both for my scooter and for the packaging, and when I lined it up against the original one I could detect next to no difference in circumference (the older belt was very slightly larger in diameter, which I expected). I only replaced it anyway as part of the overhaul, not because it appeared overly worn. I just suspect it when I smelled the hot rubber.


Which, by the way, do you think is being caused by what, exactly? My own mortified guess is that it might have been the smell of the O-rings around the piston overheating/ decomposing, and if so, I am obviously screwed. But thoughts on that? Are there any other rubber parts involved here that might have been getting much too hot somehow?


Since I am able to force it to roll forward, I am guessing my best move now is just to try to get it home (since there's no way I am performing a repair on my cylinder along the side of the street in Los Angeles). Will it be damaging to the piston/ cylinder for me to even force-roll the scooter up a ramp and into some kind of moving truck, do you think? I obviously can't tow it by raising the front tire since the back one is the one that won't rotate.

When we (myself and 3 other friends who play with Zuma's) have had a lean seize, the scooter is rolling along, stalls suddenly, the smell of burning rubber fills the air and the scooter will usually start back up-with slightly less power. The rubber smell is from the motor locking up for a second, allowing the belt to slip over the now stationary variator because the scooter was still going forward and the rear wheel is still turning. I run a rpm tach and temp gauge with the appropriate alarms set to notify me of pending doom. We initially set the motors using a much more sophisticated equipment (I work in engineering at a small engine company.) but stuff does fail and weather changes can affect out tunes. I now prefer nothing more than a Stage 1 set-up.

When my Zuma 125 blew a belt in the middle of nowhere, I called a friend who owns a tow truck company to rescue me. Wife was with me so no pick-u truck. The tow truck had option to haul a motorcycle in a one piece track. I should have taken a picture, it was really nice. Loaded on street level (my rear wheel was locked TIGHT) then strapped down and raised in the air. So any movement with yours is still movement. I would get it home if possible. I still think its a lean seize.....

Another concern: When I stopped the first time to open up the crank case, I did not replace the gasket seal: it had a tear in it anyway at that point. This means my crank case was not sealed when I drove the scooter the second leg. I've heard that a faulty or absent seal on a crank case can cause oil to get sucked into the crank case from the gear box.... Which would mean I am REALLY screwed. But is this true??

What case gasket are you referring to? The gasket that goes between the case and the cover to the transmission/vairator and clutch assembly? If its that gasket, we never use them. Heck, I've ran with no transmission cover at all for a week while I was trying to figure out a clutch issue. If your referring to the gasket that goes between the reduction/gear box cover to keep the ATF fluid in, we've re-used ripped ones many times. As long as there is no leak youre fine.

Now, what I forgot last time. If you had a soft seize and the belt slipped on the variator-there is a chance the belt either got jammed (usually it turns sideways and wedges someplace horrible) or it put excess stress on the V-slides/rollers/clutch assembly and broke something. Again, keep us posted. I have faith it can be fixed on the cheap with either OEM used parts or pattern replacements.

So, any updates?

Gearboxes need 90W oil not ATF

Update
 

The gasket I meant was the crankcase gasket, the one that goes all around the crank case, not the one by the gear train. I read somewhere that the crank case without the gasket on it can create suction and end up drawing transmission fluid into the case, drying out the gear train. But maybe that is not so.


The last time I checked the v-belt (along the roadside when the scooter died the first time) it looked just fine. I am doubtful the problem is there, but I haven't opened it up a second time to verify. I finally got the exhaust removed and had a look at the piston. From what I can see, it looks fine. I put some 2-stroke oil into the spark plug hole to lubricate it, and turned the rear wheel to move the piston up and down. It seems lubricated....


...But! Should turning that rear wheel be moving the piston at all? I don't think it should. The piston is supposed to drive the wheel, not the other way around. What does this tell me? Anything? Also, the wheel seems wiling (reluctantly) to turn forward, but it is the reverse direction that it fights me (I can roll it in reverse, but it really doesn't want to go that way).


I have not tried starting it up at all. That seems foolish for now, yes?


Also, regarding gear oil: I can get some 90W on Amazon, and will do so. Given that I have already used ATF, what should I do now?

Ok, heres my take on it from the other side of the country. If I was in your area I'd be more than willing to take a look at it. If you are 100% sure the piston looks ok, and it was not a lean seize, then something went in the transmission is my guess.

The rear wheel should turn freely with the scooter OFF and at idle. The belt will always rotate when the scooter is running, but the rear clutch assembly disconnects it during idle (and in the OFF position). BUT, if the variator is not returning back to its normal position, weird things happen as well.

So you either have something wrong with the clutch if its still "engaged" while OFF or idling (broken clutch spring(s)?), bell came loose-backed off, torque (contra) spring may have jumped the retainer cup. If you do burnouts, they kill a clutch assembly FAST! I know all to well.....

If the variator failed, it might be a v-slider cracked/broke, roller shattered and/or the variator nut came loose. Impact wrenches are no substitute for a proper holding tool and torque wrench.

Finally, if the reduction box final gears failed from improper spacing, the either ate the end bearing(s) and/or shattered, locking metal chunks INSIDE the reduction/gear box.

I have seen, and fixed, all of these at one point. I love Zuma's and we keep enough parts on hand to do full rebuilds of anything that can/will fail. Let us know what you find.

Opening 'er up
 

Got your message. I guess I am going to be opening up first the crank case and having a look at the variator (which I will be taking apart) and second the gear box and seeing what is going on inside there. It sounds like I have to find SOMEthing wrong with ONE of them, given the symptoms I have here (still don't understand why rotating my rear tire is causing my piston to move, though, 'cause it seems like it shouldn't and the fact that it does seems like it aught to be telling me something important, but I dunno what that is).



Will be reporting back once I have done these things. Fingers crossed! Thank you for staying with me here! I ain't done just yet!!

More
 

Crank case opened. Variator looks fine. Turns counterclockwise with no difficulty, rear wheel turns accordingly... V-belt is in perfect condition, nuts on both the variator and clutch are holding fast...

Next...
 

Variator is now off. Rollers are all fine, variator is fine. Clutch also removed. Also seems to be fine. Next is the gear box...

Gear box
 

Have drained the gear box. The fluid is clear, has no chunks in it, the color of maraschino cherry syrup...

Before the gearr box
 

Before I open up the gear box...


...Let's assume there had to be a lean seize: I know I was opening up the air jet to try to lean out the fuel, and I am certain (now) that I opened it up too far for its own good, not knowing what the consequences would be. In fact, let's say 100% that's it. It has to be.



My rear wheel is still turning, albeit reluctantly, and in one direction more than the other. Let's assume I have lubricated the cylinder, and that the wheel does turn somewhat (the seize is not total). I want to get the scooter back to running like normal again. Also, let's assume (because it is true) that I did not have a good seal at my exhaust port, and that I now have a new gasket for it which should make a very tight seal (because I do, and it should). What would I have to do now to get it running? Replace the o-rings on the piston? (Remove the cylinder head et al.) Because I am all but certain that this is what I have going on here.


But does this explain the fact that the rear wheel is still turning the piston when the scooter is off? Also, when I turn the variator now, I can hear the piston going "thump thump" inside the cylinder, like it is making a seal in there and "popping" when it reaches the exhaust port. Should it be doing this? Is this a good thing or a bad one? (or maybe it makes no difference).

Gear box
 

Gear box now open. Nothing unusual inside. Rear wheel turns freely now. Please advise.

The rear wheel should spin freely, like any scooter out there, when in the OFF position or while at idle. Even if the engine grenades, it (rear wheel) should still spin freely. You said the wheel spins freely after pulling the reduction box cover off, and the ATF fluid looked metal free, what does it do when you put the cover back on? Side note: Someone said not to use ATF fluid, I agree. Use whats recommended in the owners or service manual. We use 10-30 fully synthetic motor oil.

I still think its a lean seize. You want to look at the side of the piston thru the exhaust port. Spark plug color should also be an indicator. Is it the lovely mocha color? Brite death white? You could also do a compression test. You can "rent" them for free at most major auto parts store. I dont have a service manual handy with the compression specs. If you do a compression test, do multiple (3 or 4) completely from start to finish. Sometimes those things dont always seal 100%, so do multiple test and average the numbers.

One last wild card. There is a chance that running it with an exhaust leak caused a reed pedal to crack/chip. The stock metal reeds hate expansion chamber style exhaust also. The metal reeds will destroy the piston when they fail, and if the damage goes past the piston skirt, your main bearings will be shot as well.

If Zumaforums was still active, you could have found someone 2-stroke savvy in your area easy. Its a FB page now from what I recall. Be warned if you go there! Stupid questions will get stupid answers! Its a trial by fire but as a whole they will eventually reach out and help.

But in a nutshell:
The rear wheel should turn freely when OFF or idling. It should NOT be tight or turn with the motor when OFF or idling.
IF it does, the clutch is hanging up or the variator is not seating correct.
IF the rear wheel is dragging, I bet $5 the reduction gear is not spaced correct. It will bind and drag, sometimes worse when hot.
IF you had a lean seize, there is a chance it might run for awhile again.
BUT STILL find the base/factory settings and set the carb BACK to stock!
IF some old man tells you your scooter is running rich, rev it a couple of times and choke him out with the sweet smell of 2-stroke! Then ride off into the sunset, leaving a cloud of bug killer behind you!
LOOK again at the side of the piston thru the exhaust hole.
LOOK at the plug color and for trash in the plug gap.
LOOK thru the piston hole and see if there is a hole in the top of your piston. A compression test will reveal this as well.

Thats the extent of my powers from across the country. I wish I was closer, but there is SOMEONE in your area, you just have to find them. I've met some interesting people thru scooters and bicycles. I help 3 people with cheap transportation needs. 2 scooters that are their only transportation and one guy with just a bicycle. Got so tired of working on old, worn out bicycles I gave him my Fairdale Taj 26". $500 to me is like $5000 to him. He pays it forward as much as he can.

Again, let us know your findings. And fingers crossed/thumbs pressed (German saying) that its something simple!

If the wheel turns when you turn the motor by hand (or by turning the wheel it tries to turn the belt/variator&motor) then the clutch is definitely holding/stuck in some way keeping it engaged. Open up the clutch to see if any of the shoes (or any broken pieces causing it to bind) are stuck against the bell. Betchya if you free the clutch, the wheel should turn easier because it will not be engaged trying to turn the belt which is connected directly to the variator which is directly connected to the engine crankshaft. With the bike NOT running and up on the center stand, turning the rear wheel will turn the bell through the final drive transmission as normal but should not be trying to move the belt because the clutch should be disengaged.

Fix your clutch!
(but you may have possibly done some engine damage too... which is a separate issue apart from the clutch)

Oh, and it should be easier to push the scooter (if the clutch is still stuck) by removing the spark plug... then you won't be fighting the engine compression of the piston stroke.
(and I don't even own any 2 stroke stuff, but did once upon a time... ultralight aircraft engine. It was a thing of beauty; Rotax 503 electric start+ pull start, 2 cylinder, dual carb, dual ignition)

Clutch!
 

So when I reassembled the gear box and re-attached the clutch, v-belt, and variator, the problem continued. But I figured out what was causing it: for some reason, when I screw down the nut on the clutch bell, it causes the rotation of the rear wheel to rotate the entire clutch (as though I had the engine on and was driving). When I loosened this nut, the bell stopped rotating and the rear wheel could rotate freely (and didn't cause the piston to move). It seems something about my clutch and its bell is (right now) causing it to be continually engaged, but whatever it is, it isn't the tightness of that nut alone: I know that the nut has to be screwed down SUPER tight to ensure the bell doesn't come loose inside the crank case! Maybe I am missing a washer somewhere (don't remember there being one to lose, though).


But whatever that problem is, I am considering it minor (for now) compared to the weirdness I experienced while driving a few days ago and the way my engine died in a lean seize on the way home. Haven't opened up the cylinder or tried to remove the piston yet, but am thinking maybe that is going to be next. Any advice on that is welcome!

Nothing in that transmission is higher than 40nM. We set both cluch bell nut and the variator at 40nM. I dont have a service manual to see is there if there is a washer, but you could always go to Cheap Cycle Parts and look at their exploded parts diagram. See if everything looks correct. Just looking inside the exhaust port with the piston forward, so you can see the side of the piston, will tell you if you had a lean seize. Spark plug is also a good indicator.

Sometimes, when you have a lean seize at speed, it will reveal everything thats wrong in the transmission.

Off the top of my head, I have no idea why tightening the bell down would cause the symptoms you described. Will think about it in the morning.

I have an ebike and my front wheel caught a transfer on the road (from milling and paving) and spit me off the front at 22mph. I hit the ground HARD, and as a bonus, got a chunk of my hair torn out! I need a bicycle helmet! Road rashed my knee and elbow, have a huge rash on my head and a chunk of hair missing. Ouch! Anyways, will give it some thought in the morning.

Holy mackerels!
 

DUDE! YOU NEED A BIKE HELMET! People don't realize just how dangerous a "simple bike" can be! At 22mph you are almost asking to be killed! And I still NEED YOU!


Tell me if this is what a lean seize looks like...
https://photos.app.goo.gl/SywYSJ2Z9EYyYVKG6

https://photos.app.goo.gl/SywYSJ2Z9EYyYVKG6


Aw, hell, I know what a lean seize looks like by now, and I know this is it. BUT! I have now polished that piston up, and though some of the scratch marks are still visible, I'd like to know if you think it might be at all worth my time to go ahead and polish up the cylinder as well, add new gaskets, put it all together again, and hope it will run. Here is a photo of the polish job on the piston:

https://photos.app.goo.gl/6Bm4fwrTvpCojPYMA
https://photos.app.goo.gl/6Bm4fwrTvpCojPYMA


Stay off that bike until you have headgear!!!

Actually, no. That piston looks normal, at least in the pics. I had a lean sized piston I saved for an example but I think it got tossed when the garage was cleaned.

If in fact that was a soft seize, it was super soft. I had one once going to work. I pulled over, got it started, choked it (I run manual chokes) to flood/cool it down and re-adjusted the carb. It was 26 degrees out and the scooter carb was set for summer weather. That scooter never seemed to notice, though looking thru the exhaust port you could see one good, deep scratch.

There is a chance that when, whatever caused the transmission failure, it perfectly matched a lean seize in symptoms. Its just not normal to have the clutch constantly engaged like you describe when the scooter is OFF or at idle.

And yes, I can still go to my local bicycle shops. They are practicing "social distancing" but I may go Sat. and look for a helmet I like. The ugly rash and bald spot from having my hair torn out meaning I'll have to wear a do-rag to try them on. Looking into a Nutcase brand.

Do you think, then...
 

So those scratches on the piston don't seem all that serious to you? Gosh, I hope you are right! Although if so, then my problem, whatever it was, still remains... Do you think, then, that the problem all along has been something inside my crank case? This would explain why my rear tire wouldn't move after the second breakdown, I guess, since if the clutch bell somehow got "locked" to the clutch proper it would have become very difficult to turn the wheel (which, as said, it was). The symptoms certainly seemed to fit with a lean seize, but maybe not?



Okay, now I have to go back down to the scooter and have a more serious look at that clutch and figure out why it was staying engaged. If nothing else, I have at least given my cylinder and piston a thorough cleaning and overhaul and new gaskets, perhaps forestalling possible future problems there! (though let's be honest, it's a 19-year-old machine, and things are gonna give out on it from time to time— but it's all I got to drive!).


...Sometime later...


I think I have the clutch thing figured out. I had removed the bell and was looking at the big nut that holds the rest of the clutch together. It seemed to have circular wear marks on it. I thought this was strange. And when I screwed the bell on tight, it seemed like this is where the bell was coming into contact with the rest of the clutch.


Well, it WAS where the bell was coming into contact with the clutch: because I had not screwed that nut on super tight when I had finished replacing the springs on the clutch shoes, and that nut was slowly coming loose inside the crank case, pushing it up against the bell.


I feel a little like an idiot here, but bear with me as I tighten that nut down, reassemble the clutch/ variator, re-seal the cylinder, lube it up, and see if it runs. Oh, and return the air jet to factory specs. Of course. Wish me luck!

So it turned out that big, thin nut that holds the clutch assembly together came loose? If so, you found out what was going on. There is a special tool that locks that whole assembly together. The clutch springs and/or the torque (contra) spring can be changed without the tool, but the tool makes it a easy!

You can get the socket for that nut from buggypartsnw.com. They sell a dual sided socket that has both 39 and 41mm. We get individual sockets from Northern and have the inner bevel planed off for a better fit, but the buggyparts one works very well. Forgot the torque on that nut though.

Side note: I never would have removed the cylinder if there were no scratches on the exhaust side of the piston or if there was not a hole in the top of the piston. That was just extra, unnecessary work. At least you now know the top end is all good.

Get it back together correctly and let us know if all is well. Zumas are quality, tank like little scooters. I've owned at least 6 in the past, 2 of those pre-bugs. You have a bug-eye. Good luck getting her purring again!

And still...
 

Time for an update!


After cleaning up my piston and cylinderI ordered replacement gaskets for the head and base. Finally, a few days ago they arrived! Yesterday I went down to the scooter and installed them. I made sure the cylinder head was very smooth and that my gaskets were seated correctly. I got the piston back in the cylinder (NOT easy!) and got the head on top of the cylinder. I cranked down the four bolts that hold the cylinder and head in place. I put the spark plug in, I reattached the electrical connection to it. I re-attached the air filter (also NOT easy). I put the crank case cover back on the crank case. I put my key in the ignition. I said a prayer to some heathen gods. And I gave the kickstart a good solid push.



Nothing.


I checked the kill switch (that one has fooled me before) but it wasn't set to kill. I tried the kick starter a few more times. Nothing.


I checked the spark plug— apparently I hadn't tightened it down, had just put it in finger tight. I was sure I had found my problem! I tightened it down, re-attahed the electrical cable to it, and jumped on the kick starter.


And still... Nothing.


The kick starter is moving the piston in the cylinder, and I can smell gas, but there isn't anything like ignition happening inside there at all. I didn't mess with anything electrical other than removing, cleaning, and reinstalling the spark plug. But I am not getting even a glimmer of life from it now. It's like everything is in place, but the damn thing has chosen not to cooperate with me any longer.


Got any thoughts on that? I am exhausted and it is late and I am going to bed now. So, so disappointing. :no:

Just got in from work-in the rain! Yuck! So I'll give you a quick idea. Are you sure you are getting spark? Hate to say it, but if we have that problem and suspect spark-someone holds it while the other person hits the starter or kickstart. It will wake you up! You will know you have spark! You can also use a spark tester but I have terrible luck with them.

Next up, compression test. There is a chance you broke a piston ring. That would make the compression to low. Or something WAS wrong with the piston. Did you remove the reed cage? If so, did you inspect the reeds? I don't think reeds are you problem but it could happen.

Make 100% sure you didn't pinch the oil supply line when putting the shroud back on! Just double check its not pinched! That will cause problems later once it gets running.

Last thing I can think of. Make sure nothing is stuck in the spark plug gap. I sold a Zuma not long ago and the guy called me saying it suddenly quit starting. Ran great, then never started. Turns out is was a piece of something in the plug gap. Knocked it out and it ran great again!

That's all I can think of right now. Good luck and keep us posted!

Let's say
 

Let's say the piston rings are probably fine— I was very careful about inserting the piston into the cylinder, and did not force it in, and I never removed the rings from the piston, so I consider a piston ring failure to be pretty unlikely. I also had a good look at the spark plug when I removed it briefly before tightening it down into the cylinder head, and it was clean. The fact that I am smelling gas suggests to me that I am getting compression (probably), but just no ignition.


Let's also say that I test my spark plug with a multitester, and I find nothing wrong with it. And let's say I test its spark by removing it from the engine block and grounding it out, but find no spark when I use the kickstarter. I have not done these things yet (I will very soon) but my sense is that this is what will happen when I do.


And lastly, let's keep in mind that none of these things are related to my original problem, so whatever the problem is now, it has to be the result of something I must have done in the course of trying to smooth out the piston (i.e., removing the cylinder, replacing the gaskets, etc.).


If any of that is helpful, let me know. Will let you know what happens with the spark plug test later today. The beat goes on. La di da da di, la di da di da.

If you ground the spark plug to check for spark, watch out if there is still gas/vapors in the cylinder-it will turn into a flame thrower! Get a cheap spark tester from a auto parts store.

Another thing, did you point the arrow on the piston toward the exhaust port?

Cracked reed pedal will also prevent it from starting. The reeds don't like being ran with an exhaust leak.

After you verify your'e getting spark, you could always use a dash of starter fluid to help bump it over. If it still won't start you'll need to do a compression test.

I wish I knew someone 2-stroke savvy in the L.A. area. Know a bunch of lowrider car guys and a few bands, but no moped/scooter guys out that way to send help. I kinda regret tossing that low miles stock top end in the recycle bin now. There is Myrons Mopeds in Fullerton. Shaun is a good dude and knows his 2 strokes.

News of the day
 

Your offer to put me in touch with a person out here who could help me is very generous. There is nothing like a personal network connection to actually get things done! As it is, though, it seems like I am on my own for now.
I tested the spark plug, and had some surprises:
The plug tested out just fine as far as resistance goes, so I grounded it and cranked the kickstarter. It sparked! A bright blue-white spark came shooting right across the gap, just as it should! I was pleased, and put it back in the engine. This time, there was something like turnover happening. The engine didn't exactly catch and start turning over on its own, at least not at first, but I tried cranking it again a few more times and one of those times the engine actually ran for a second or two on its own!
But it didn't sound right. It's hard to put my finger on it, or describe the sound itself, but it didn't sound the way I know it should. It also wouldn't take off like that a second time for me. But it shows me that I am getting ignition. So my guess now (and probably yours as well) is compression. If I have a leak anywhere around the cylinder base, head, or spark plug itself, this is the kind of response I might get from the engine. "Yay, fuel! Spark! Ignition! Move that piston! Oh, wait, not enough compression.... Sorry! Goin' down!" I've had a compression issue once in the past, and it sounded like a giant dragon fly was inside my engine— it was the sound of compressed air escaping around the cylinder (oh and yes, quickly, I am sure the piston is facing the correct way, I was VERY careful about that! The arrow on the head of it points towards my exhaust port!). This didn't sound quite like that, but it could certainly still be the problem here.
Or, as you said, it might be the damn reed valve. That's one part I have not taken out and had a look at yet, esp. because it isn't terribly accessible. But as you said a cracked reed would also prevent me from getting proper compression in the cylinder. Are there tests I can do to see if my cylinder is leaking somewhere first? I can also try tightening my cylinder nuts down just a bit tighter and see if that helps at all. But I feel good knowing that at least I don't have an electrical problem and that my spark plug is working as it should.
Thank you for continuing to engage me here. I really appreciate the willingness to keep with me and help me try to solve this problem. That means a lot.
....
Later that evening...
....
Okay, I went down and tightened up the spark plug and cylinder nuts again, and gave the kickstart a go. The engine caught! I was amazed! It still didn't sound right, but it was running! I let it run for 3 or 4 seconds, and pondered taking it off the kick stand and driving it around the block. But then things suddenly changed: the speed of the piston in the cylinder picked up, and the sound coming from the engine became much more raspy and loud. I shut down the engine immediately. The sound was unlike anything I have ever heard before coming from the scooter.
It seems that I am finally getting compression, at least briefly, inside the cylinder. But the rasping noise? Would a cracked reed valve petal make a noise like that??
One more thing: I noticed when I put my air filter box back on that there were some cracks in the elbow joint where it attaches to the carburetor. I assume I will now need a new air filter box. The cracks mean that some unfiltered air is now able to get past the filter and go straight into the carburetor. Would this be causing the sounds I heard?

A cracked/broken air box is a death wish to ANY motor, but its extra bad for a 2-stroke because they are so sensitive to everything being correct. Pattern replacement air boxes are the way to go. Scootertuning.ca and sometimes Scooter Swap Shop have them for good prices. Or get a OEM one for a bit more. Don't be tempted to get one of those pod style air filters, they require jetting changes. Stick with stock or pattern replacement. If its just the elbow that looks cracked, that's normal. The rubber coating on the elbow flakes from age/heat and makes it looked cracked.

Be careful when tightening down the head screws. I forgot the torque vale but it needs to be done at the correct torque/evenly so the head doesn't warp.

It you had a broken reed it wouldn't even start. So your'e fine on the reeds. Plus, the reed cage is a PITA to seal when re-installing. So any reason not to remove it is good.

That sound you hear is a new one to me. Never had a noise like that.

My Zuma is still in a million pieces. But typing to you has kinda motivated me to get it sorted and put back together.

Again, good luck on figuring it out. Asked around to the lowrider guys and they don't know anyone who messes with "mopeds". Worth a shot though.

I went ahead and checked the reed valve: it was fine, some of the petals were a little loose, so I gently curved these into a flatter position, made a new gasket for the valve, and re-sealed it against the engine block. The trick right now is how to re-attach the valve to the carburetor: apparently it has to go down quite a ways! I didn't realize how far when I took it off. Wasn't able to do it using just my hands, am considering wrapping it up with a ratchet strap and seeing if I can force it back together that way. The rubber of the join here has to stretch a LOT go get back on that carburetor!

Anyhow, I think the reed valve is not the problem. What I really aught to do is get a torque wrench and use it to tighten down the cylinder nuts to spec, it's just more cash that I don't want to spend (I ordered a replacement elbow joint for that air box, another $15 for a piece of rubber I won't have for another two weeks) and I've managed to tighten them down once before without said wrench and got compression. Of course, the risk of over-tightening the nuts is pretty horrendous (stripped cylinder posts, I know), but it looks like the only possible remaining problem here is the seal around my cylinder, yes? And if I can get that to seal, I should be golden....?


It seems like every time I turn around, I find another part that is slightly damaged or out of alignment or needs partial replacement. I guess that is part of owning such an old machine. Sure is a pain in the ass though. I am not sure how much cash I will have spent with this repair that began as an attempt to lean out my fuel supply and inflate my rear tire (!) but I think it's on the order of a couple hundred bucks so far. To say nothing of all the labor and the time, both yours and mine! I am learning something as I go, which I guess is worth something somehow. This damn bike better last for another 10 years problem free! (I suppose that is too much to begin to hope for... considering that it still isn't even running normally yet).

I had a Stage 1 modded Zuma (exhaust and transmission) and that scooter had 30,000 miles on it when I finally sold it. It was a 2005 year.

My friend sold his Stage 1 modded Zuma with 45,000 miles not long ago.

Wear and tear were drive belts every 10,000 miles-did the rollers at the same time, tires, air filters every 10,000, reduction box oil every 10,000, front brake pads when needed and other small parts that need random attention.

You can "rent" a torque wrench for free from any major auto-parts store. And again, I wouldn't have touched the reed cage. The "sloppiness" is normal for the reeds.

Does your electric start work? Why are you kick starting it every time? I ask because are you sure nothing is acting strange in the transmission, causing the weird noise you hear. Wal-Mart sells the battery for the Zuma (Everstart) for a great price.

Nothing else is popping in my head right now. We've see all sorts of stuff fail from doing wheelies, DON'T do burnouts, nose wheelies/rolling endo's mess up shock seals and other abuse related issues-so we have a pretty good knowledge base.

My wife was suppose to go to Oakland, CA but the pandemic stopped that. She was gonna drop thru the L.A. area when returning (Driving cross-country with her sister). She knows Zuma's VERY well! She's been helping with everything from tires changes to full engine builds. Rescued us on rides and helped fix stuff on the side of the road. I bet she would have figured it out quick! She started on a Stage 1 modded Hyosung Sense (great little scooter!), upgraded to a Buddy 125, Cam-Am Spyder (P.O.S.) and now has a Honda Silverwing scooter.

Again, best of luck figuring it out.

Once again, covid-19 stands in the way of my possible future success! If your wife ever decides to travel again and makes that same trip, and if my scooter is in any condition other than perfect (which is most of the time) I'd be thrilled to have her take a look at it! (How can I entice her? Food? What can I bake for her??).


Regarding the kickstarter— yeah, fair question. The very first thing to go on the scooter was the push start button. The machine was even still under warranty, but I didn't want the hassle of bringing it back to the dealership for something I could work around so easily.


And then some time later I had a little accident with the bike, and broke off one of the rear blinkers, so I made custom ones to replace them (they're pretty neat!) using high-power LEDs. But in the course of adding wiring for those LEDs, I did something that caused my battery to slowly drain down to nothing in about an hour of non-use, and I could not find where the short was, so I took the battery out and replaced it with a thing called a "battpack". It's basically a very large capacitor that sits clamped to my frame, and it works (has worked) perfectly. Only drawback is that I only have power while the engine is running, and I have to keep using the kick start to turn the engine over. But no internal battery at all! It's been like this for over a decade. I had no idea batteries were so superfluous, but it turns out they are. (technically this modification is illegal, I forget why, please don't tell the sheriff!)


If you have any suggestions on how I might shove the carburetor back into the rubber joint of the reed valve, I am all ears. And again, ask your wife what I can bake for her if she ever comes this way! It would be a treat to show my bike to someone (anyone, really) who gives a damn about Zumas!

I put a tad of grease around the carb lip to help it slide in. They (intake/reed assembly) tends to get a bit hard with age. But it can be done relatively easy. I also hate the air filter box back onto the carb. You have to make 100% sure its seated or it sucks in raw air. One of the WORSE air filter assemblies to put back on is a OEM PUCH moped air filter. Worse vehicle, 80's era Toyota Vanwagon.

I think she ditched the cross country trip as of now. One of her sisters lives in Oakland, and a friend in a band lives across the bridge. It's funny, I'm in my late 40's and she's in her mid-60's and we know so many grindcore and hardcore/pink band members. Those are the fun, interactive concerts! This Covid needs to leave so we can resume going to fun shows again!

Quick thing to point out. Sometimes the kickstarter gear will stick a bit when coming back up. It will start with a tingling sound and get worse as its ignored. Next time you kick it, pull the kick starter up with your foot. I don't think thats even remotely your issue but you never know.....

Tip
 

I've discovered this about air filter boxes: if you blast the rubber elbow joint with a hairdryer on its hottest setting for like 30 seconds, you will soften it up nicely and it will slip over the port on the carb oh so easily! Someone borrowed mine which is the only reason I haven't tried this with the reed valve joint yet. The dude is supposed to be bringing it back tomorrow. It makes a HUGE difference, and everyone working with scooters or motorcycles of cars should practice this tip! Heat that bugger up first! (er, but don't use flame to do it, for what might be obvious reasons).

Variator
 

Hm. I opened up the crank case (yet again) and it turns out my variator nut was coming loose. I could have sworn I put threadlocker on it, but apparently not. I have put threadlocker on it now, however, and tightened it down well. Am just waiting for it to cure before I try starting it up again. I have put some sealant around the cracks in the air filter box which I think will hold it until the replacement elbow joint arrives in a week or so. I still haven't gotten my torque wrench, but I have tightened up all of the nuts around the cylinder head as well as the bolts around the reed valve as tight as I dare. Stripping any of these would be a disaster.


My mother has suggested I get an electric scooter and ditch this project altogether before it gets more expensive and still doesn't work. If I had a charging port ready to go for my parking space, I wouldn't hesitate. I do intend to make the switch to electric at some point, but I am so close to finishing up with the Zuma that I can almost taste it. I think!


... Less than 20 minutes later...


Well, it runs. I wasn't sure it ever would, but it does. It's making large plumes of noxious low-lying smoke as it does, so there is still some adjusting to be done somewhere, but the damn thing runs again. How about that??

If I would consider an electric scooter, it would be a NIU GT series. But, I got into electric bicycles (Pedego) instead. Get by with a bicycle helmet, can slip onto a sidewalk and I have a extra charger at my work. Removable battery is the best.

I want a AddMotor MOTAN M-66 R7. Step-thru, 25mph and mag wheels. And cool options! I'm just not sold on the product support right now. So I'm still waiting for my dream electric bike......

Take it (Zuma) out for a ride and see if the "smoke" burns off. There's a chance you flooded the exhaust and whatever is in there will/should burn off. The variator nut should be 45Nm. A impact wrench will work, but I personally don't recommend it. Your'e lucky the nut didn't come off and knacker the end of the crank shaft! I bought a Zuma that had that happen. Somehow I tapped the end of the crankshaft and it worked like new! It was TRASHED! I got lucky!

If you knew someone that was trustworthy I would pay them to go thru everything instead of replacing the Zuma. Hopefully, all is good and it will serve you for many more years.

Again, good luck and hope all is well!