Odd Stalling Problem

[Ebuddy]

My Roketa MC-30-150 (B GY6 variant) starts and idles awesome. When on the kick stand, I can rev it up to 7,000 RPM up and down sustained and quickly release and it goes back to idle without a hitch.

When I ride it, it runs and accelerates great. After, say, 1 minute or two at higher sustained speeds (35mph +), when I slow down (like for a stoplight), it slows down and then dies. Following this, it's VERY difficult to re-start it, almost as if it's flooded. Once it does restart, it seems fussy for a short time and then the problem repeats.

When I get it back to my garage and start it up, it starts and idles fine and I can play with the throttle with no issue.

It's almost like it's flooding...but not quite. I don't know what to make of it. I presume the carb is fine since it otherwise runs and idles with no problems but it SEEMS like a fuel delivery problem. Valves were adjusted just a couple hundred miles ago and the issue's gotten progressively worse.

At first I thought that somehow the belt/clutch/variator was somehow getting caught but I replaced the belt and installed new rollers (yea, sliders would have been better, but it only needed to get me until the spring). Everything seemed to look and operate normally.

Any other ideas? I'm going to store it for the winter soon, but want to be ready in the spring.

Thanks! =)

[blueboy5000]

Sounds like valves. Adjust your valves to .004" intake and .005" exhaust.

[qwertydude]

Those symptoms are of a bad fuel pump. Chinese fuel pumps are notorious for this. Best to replace it with a real Mikuni fuel pump.

http://www.amazon.com/Mikuni-Genuine-Single-Fuel-DF44-211-D/dp/B000GTV9AK/ref=sr_1_3?ie=UTF8&qid=1382581088&sr=8-3&keywords=mikuni+fuel+pump

Scooters with the tank in the floorboard need a vacuum operated fuel pump to pump fuel up into the carb. The Chinese ones simply can't pump with the reduced vacuum of high rpm running. The Mikuni's can.

Best thing to do is a desmog since these scooters benefit greatly from that. Then get a new fuel pump and run it on it's own dedicated vacuum line to the intake manifold that's as short as possible and has no T's. It shouldn't if you desmog the scooter.

Those two things thing usually solve the mysterious high speed bogging issues people experience.

[skuttadawg]

Check the valves and adjust if needed http://www.scooterforumonline.com/index.php/topic,1720.0.html

[Ebuddy]

Thanks guys! I think I will get a new fuel pump. The one on there is the original, but the scoot has about 4k miles so even if it doesn't fix the issue, it's cheap insurance. The only thing is the the scoot doesn't "bog" at speed, it seems to run fine, it's when I decelerate to a stop that it kills and doesn't want to start.

I did do the valves (.003 and .004) just a few hundred miles ago but I will recheck them also.

[Ebuddy]

Well...thanks again! I switched out the petcock and that cured about 95% of the problem. I took it out and it still stalled out twice, but was easy to restart after. Since I've probably been fighting the old, failing petcock I figure I might re-look at the fuel/air mix and idle speed. Nonetheless, she's running well enough to get me to my storage destination! =)

One follow up question: The scoot has the B-variant, long case and 13" wheels. The boss (my wife) might let me get a new motor over the winter. If so, would I be OK with a "standard" GY6 150cc long case?

[blueboy5000]

The "b" variant is theoretically the fastest gy6 150cc engine. Are you certain it has a "b" variant, as the "b" engine is used EXCLUSIVELY with 16" wheels?

If you have good compression and are not leaking/burning oil, then I see no reason to buy a new longcase. 4K is really not bad as far as mileage goes, I know of a bike with a 157 that is at over 15k and runs like a champion.

[Ebuddy]

Yep... Engine S/N starts with "BN157QMJ". It does have a small oil leak that isn't TOO bad. It's probably small enough that it can go between oil changes and still not be super low. Besides that, there is a stripped screw hole for one of the screws for the oil pan. I am debating at the moment, a local, trusted scooter shop in town can sell me a very slightly used motor pretty cheap so I was kicking around the idea.

[qwertydude]

So it does sound like a fueling problem. I can almost guarantee you a full desmog plus the new fuel pump will fix the stalling problem.

[blueboy5000]

That's not a "B" variant, the two variants are "P" and "B" and they read like this " 1B57" or "1P57". The "b" engine is also called an "extra-longcase" as it is significantly longer than a "longcase" to fit 16" wheels. The 'P' variant has larger valves and a taller head, resulting in nominal low-end power gains over a regular 157.

[skuttadawg]

If the tank is higher than the carb no need to get a fuel pump . Most have the tank under the seat or behind it , but a few have the tank in floorboard . Those with the tank in the floorboard a vacuum Mikuni fuel pump would help a lot .

When the valves are too tight they do not open up enough to allow fuel and air to start and keep it running . Way too tight = no start . Tight it starts but stalls once the engine gets warm . My Echarm they got too loose and it would want to stall just before coming to a stop but start right up . After a valve adjustment it was new again and has been for over 17k miles

[Frank Castle]

So it does sound like a fueling problem. I can almost guarantee you a full desmog plus the new fuel pump will fix the stalling problem.

what does 'desmog' mean?

[Ebuddy]

Hey guys! I'm back. I brought (rode) the scoot home from it's storage place. Started right up and ran like a champ. Same issue however, after it's warmed up it gets fussy and dies on deceleration and is sometimes difficult to restart. It does have the smogger "stuff" still in it and I've reviewed a number of online pages but I'm still not entirely certain what I should/should not remove. I'm attaching pictures of the inside (if it works). I understand how the fuel is fed via vacuum to the carb but there are some extraneous tubes that I'm not sure of. This weekend I might try to re-gap the valved to .004 and .005 for intake and exhaust respectively. Finally, should the various tubes for fuel, air, etc. (other than the obvious ones that are MUCH larger) all be the same size? It seems (using the same size all around) sometimes they go on snugly, others are loose any yet others need to be wrestled on the various fittings. Any other advice would be much appreciated! =) http://i93.photobucket.com/albums/l61/CallMeEOnly/IMAG0094_zps53155de1.jpg

http://i93.photobucket.com/albums/l61/CallMeEOnly/IMAG0095_zpsb63e78a0.jpg

[Frank Castle]

is that a soda can in your motor?

[Cubby1331]

is that a soda can in your motor?

I think its for those long rides when you get thirsty :cheers:

[Ebuddy]

LOL! Yes, a soda can. It's collecting small quantities of oil and such from a few different tubes. I suspect most, if not all of it is unnecessary. What I THINK I can do is remove the valve cover and block off all the holes in it and then remove all the pieces that the hoses were attached to it. The only thing I'm not sure of is a tube that comes off the top of the gas tank and what to do with that.

[scooter]

So it does sound like a fueling problem. I can almost guarantee you a full desmog plus the new fuel pump will fix the stalling problem.
This completely made my bike run like a Cadillac. Not one of the 80's Cadillac's, I'm talkin a post 2000 CTSV Cadillac. I think you'll figure the desmog out once you dig into it. It's pretty self explanatory honestly. If I recall you only have one vacuum line going to the charcoal canister. Remove that vacuum line and I think I put mine directly on my petcock. This leaves you with a fuel tank vent. Just vent to atmosphere with a fuel filter. I drilled a 3/8 hole and ran it out just before/ in front of my tail light and zip stripped it to the bottom of my book rack. It's not noticeable. The big hose on the valve cover gets capped/plugged. Then if I recall there is one more vacuum line that goes to the exhaust pipe crap. That get's capped. If I'm missing something somebody please jump in. It's been a few beers since my last DESMOG, but it was real easy. I do remember that. I went with all new US made hoses at the same time.

[Ebuddy]

I'm giving it a shot tomorrow morning. My intake manifold has 2 lines, one goes to a "T" fitting where one of the branches goes to the vacuum on the petcock and the other to the side of the carburetor. The other fitting on the intake manifold goes into a small cylinder attached to the frame. I'm presuming that this second one is for the smogger. So do I cap them both or just the one to the cylinder and leave the other?

[Rhompin45]

My friends was having a similar problem and the fuel tank was not venting properly. We were several miles from the house and he had to remove the gas cap till we got back. It was just a kinked vent line . But his was not on de acceleration so it might be different. It could be cogged pilot jet but that doesn't explain why it is fine on the kick stand

[scooter]

I think I only have 3 vacuum lines left. The vacuum source comes from the intake tube before the carb, after the filter. It pulls vacuum on belt housing and rocker arm cover from a Tee. Then you have one from the carb vacuum port to the brass colored cap on the carb. That's your mainjet needle diaphragm. You gotta have that! The 3rd is a straight shot from Carb vacuum port to petcock valve. You have to have that. Everything else goes. Use original ports when you do it. For example if the left vacuum port comes up and Tee's into a bunch of crap but also feeds your petcock, remove all other crap and leave that port on your petcock. This is a constant manifold vacuum source. You need the timed manifold vacuum source for your needle diaphragm, so trace the one feeding the bronze cap. Trace it to the correct port. Go directly from that port brass cap. You're good. Also check out my other posts on here. I tried to put every thing that when wrong with my scoot and a corrective action on here. Some of them have feedback from other members but most were ignored. If they were ignored I took that as a thumbs up because people will jump all in your cool aid if they think you say something wrong. So no feedback was good I guess. I think my DESMOG is on here.

[Ebuddy]

Well... she's now been desmogged and the stalling problem has been pretty much eliminated. =) Just a clarification: Today, I have 2 vacuum fittings at the intake manifold. One is sealed and the other goes to a "T" with one outlet going to the vacuum valve on the petcock and the other goes to the carb (main jet needle diaphragm). Would it make a difference if I just took 1 vacuum outlet from the manifold and routed that to the carb and the other one to the petcock?