2001 Hyosung Sense 2T Issues

[Firehawk989]

Hi all,

So I bought this 2001 Hyosung sense that had been sitting for 2 years. Replaced the spark plug, drained the old gas and replaced with new 94 octane ethanol free, removed/cleaned the carb bowl and sprayed out the jets with carb cleaner. I got it to run, but it does not run well at full throttle. It runs fine until it warms up, but then starts to sputter/backfire at full throttle and starts to smoke a fair bit when warm. Idles fine and runs ok at mid throttle, just full throttle is the problem.

I didn't disassemble the carb other than taking off the bowl, and there was definitely varnish/crud in the bowl when I removed it for cleaning. Should I pull the jets out and check them properly?

I'm thinking carb problem or maybe reeds, what do you guys think?

[50cc]

Cracked intake?

[scootnwinn]

Is it designed for the anti-detonating POWER of 94 rated fuel...?

[inuyasha]

Hi
Welcome aboard
Pleased to meet you
I would give the carburator a thorough cleaning and tune up, add some sea foam to the fuel , run that tank and see if it clears up
http://www.seafoamsales.com/sea-foam-motor-treatment/
If not then we can look into other causes
Take care and ride safely
Yours Hank

[Firehawk989]

Thanks for the welcome. I used to lurk on the old scootdawg forums back when I had a 139qmb 4 stroke, but this is my first foray into 2 strokes.

Conveniently I have a can of seafoam sitting around that I was going to use on an old car but never did. I'll throw some in the tank, clean the carb properly, and see what happens.

Thanks

[Firehawk989]

Ok, so I pulled the new plug to check it, tightened the head bolts, cleaned the carb again, and put some seafoam in the tank as well as spraying it in the carb. I haven't had a chance to run it WOT yet to check my work, but it did start right back up as soon as I put everything back together.

Anyway, here is the plug:

[Firehawk989]

Cracked intake?

Intake looks ok to me.

[Firehawk989]

Ran it today, seems to run better now! No more backfiring at full throttle, but it does still smoke a bit. Hoping that will clear up with some riding around.

[scootnwinn]

I'm no genius but I think the 2 stroke engine was designed to smoke just a bit...

[Firehawk989]

I'm no genius but I think the 2 stroke engine was designed to smoke just a bit...

Yea, I knew that, it just seemed like a bit more than I would expect, and didn't have the typical 2 stroke exhaust smell. I'm thinking a bunch of oily junk just built up in there while it was sitting and that I need to burn it out thoroughly. Seems like there used to be an exhaust leak as well, since there was some oil around the exhaust pipe flange. I tightened the flange bolts up though, should be good. Picking up a helmet tonight so I can register it and legally take it for a spin. :scoot:

[inuyasha]

Yea, I knew that, it just seemed like a bit more than I would expect, and didn't have the typical 2 stroke exhaust smell. I'm thinking a bunch of oily junk just built up in there while it was sitting and that I need to burn it out thoroughly. Seems like there used to be an exhaust leak as well, since there was some oil around the exhaust pipe flange. I tightened the flange bolts up though, should be good. Picking up a helmet tonight so I can register it and legally take it for a spin. :scoot:
Hi
Its good to see you got her running well, and its normal for them to smoke alittle and if you let them sit a while then carbon can build up and make them smoke more then normal, that should pass in time as the engine gets more use
Are you using a quality 2 stroke oil as that will help keep the smoking down
I use Royal Purple for my "April"
http://royalpurpleconsumer.com/products/hp-2c-2-cycle-engine-oil/
Take care and ride safely
Yours Hank

[Firehawk989]

Hi
Its good to see you got her running well, and its normal for them to smoke alittle and if you let them sit a while then carbon can build up and make them smoke more then normal, that should pass in time as the engine gets more use
Are you using a quality 2 stroke oil as that will help keep the smoking down
I use Royal Purple for my "April"
http://royalpurpleconsumer.com/products/hp-2c-2-cycle-engine-oil/
Take care and ride safely
Yours Hank

Thanks Hank. Pretty sure there is crappy quality oil in there right now as it came with a mostly empty bottle of generic 2 cycle engine oil. The bottle does say ok for use with oil injected engines, but I will go to the local scooter shop and pick up the good stuff ASAP.

[Firehawk989]

Finally got it out for a run tonight! Engine runs great, and the smoking stopped after the first 10-15min of my ride!

Tops out at around 60km/h with the blue CDI wire removed, so I'm thinking I need to get into the transmission now. Probably needs a new belt and some rollers/sliders to refresh things in there. Pretty good though for $400 and a few hours work! :D

[Firehawk989]

Snapped a pic yesterday:

[Admin]

Snapped a pic yesterday:



Very nice scoot!

[Firehawk989]

Thanks! The dim lighting disguises the scratches and slightly misaligned body panels. :D

[Firehawk989]

Installed a new Gates Powerlink belt yesterday. The standard GY6/139QMB belt of dimensions 669 18 30 seems to work just fine even though it's about a mm wider than the OEM replacement belt for this scoot. (666 16.8 30) My top speed went from 55km/h on the flat to 65km/h. Acceleration is a bit slower, but the belt I replaced was worn down to ~14mm, so I expected that. Hopefully my 7g sliders will arrive soon and help with that. Not looking forward to taking off the big rusty looking variator nut! Put a little penetrating oil on it to hopefully help when the time comes. (Wiped off excess and made sure none got on the drive faces.)

[Firehawk989]

So I was working on the scoot the other day and ended up snapping one exhaust bolt and then stripping the threads in the flange for the other exhaust bolt when putting the muffler back on. Bad day of working on the scoot I guess. >::doh:

Anyway, I went to go tap out the stripped hole to the next size up so I could get the pipe back on, when about 1/3rd of the way through the tap wouldn't cut any further! Backed it out and found a partially drilled out bolt stuck in the flange! I guess the guy before me must have had the same problem and half-assed the fix! :doh: At least now I know it was only partially my fault for stripping out that side of the flange.

Ordered a replacement cylinder because this one has ~8000km on it and figured it needed a refresh anyway. When I get the new cylinder and go to install it, the arrow on the piston faces the exhaust port, correct? Anything else I should do/watch out for while I have the engine apart?

[Firehawk989]

Have a feeling people TLDR'd that last post, so:

When installing the new piston, the arrow on top should point to the exhaust port, correct?

Anything else I should do/look for while I have the cylinder off?