50cc dies to 10mph when engine hot
 

Have a used Piaggio 50cc 4stroke with 2,600 miles do all my work from excellent Scootdawg instruction and Lefty from years back! Working great for 2 yrs then trans started slipping, so a few weeks ago replaced rollers, plug, found a loose hose to airbox, so it runs great now except that after running hard at 35-40mph for about 5 miles it dies down(like no gas) to 10mph. Then after it cools for 20 min to half hour runs like nothing happened. Used to put Seafoam capful in my Chinese scoot every fillup, but haven't with this yet put some in a few days ago but no change. I did empty the tank and the fuel filter is totally clean, put fresh gas in. Since I got the scooter it always had a rattlin muffler with acceleration and the shop thinks that's probably the problem. They want me to bring it in for $120 to check it out this coming Wed. But I'd like to be able to fix this myself. It seems like something is cutting the gas flow when a certain temp is reached, could it be the inside of the muffler is shot and that's creating a vacuum to restrict the gas flow? Should I take off the muffler and ride and see what happens?

Are you 100% sure its the right spark plug for it? Not some random/cheapest plug on Amazon (aka-bootleg)? Heat range is very important. It could also be transmission related. Sometimes the torque driver gets hot from a lack of grease and does all sorts of fun things. If your taking it to who I think you are, they have a pretty good service bay. But, like you stated, doing it yourself and learning is much more rewarding. I would have to see the problem in person. Oh, and I would not ride it without the muffler. Any rattling could be just a busted loose cat converter. Shouldnt really hurt anything/cause issues like your describing.

Thanks for responding! I took out the original plug and replaced it with the same NGK ER9EH($15). Torque driver meaning the pulley for the rear part of the belt under the clutch housing? So remove the fly wheel? All the youtube vids are in spanish. So would I need to just relube the inside of the pulley? The only other thing that I could have done was overtighten the driving pulley after putting in new rollers but I followed the manual "tighten the lock nut to 20NM then a final 90 degree locking" meaning I tightened it 90 degrees more. (But I've overtightened that nut on my Chinese scoot and never had a deceleration problem before.)

If its the torque driver, rebuilding it can be a PITA but sometimes they need a re-grease. And the reason I asked about the spark plug, bootleg plugs are a annoying problem. We got a batch of NGK bootleg plugs awhile back and they were causing a slight lean seize issue. Now realize these plugs were being used in temperamental 2-strokes that love to seize if given the option-but these plugs drove us crazy until we figured it out. Ugh, my eye twitches just thinking about it! I've never worked on a Piaggio 4 stroke 50cc, so Im not aware of any issues with them, things to avoid, things to look for, etc. Im to far away to take a look at it myself but $120 seems fair to trouble shoot it if you cant figure it out. If you do decide to try the no muffler test, keep it to the bare minimum of miles! Your neighbors are gotta wanna pop your tires and the exhaust pulls heat off the valves and out of the cylinder, so shortest possible runs only! It also might run slightly different without the exhaust because the back pressure will be obviously missing. Post your findings when you do figure it out!

I just thought of this. If the belt was slipping, did you replace it? If not, does it measure in spec? If the problem is transmission related, it could be a torque spring. The torque spring is the big one behind the torque driver. The 3 clutch springs might be involved also. The low miles on the scooter is whats throwing me off.

thanks again for all the suggestions. Yes the belt is in excellent condition. No slipping belt, belt tight. Just sprayed fuel starter around the carb/hoses and no increase in revs. But this is off, its hanging out at bottom of scoot but isn't this the fuel line air hose, can't find a valve to connect it to on the carb or petcock off the gas tank. Thoughts?https://photos.google.com/photo/AF1Q...LW8-EE4Qqho6Pz[IMG][/IMG]

so here is the hose:

Attachment 1105

It could be just a overflow hose. For fuel spills during fill-ups or for the carb if it falls over. I dont think it has any importance to the problem your having. Where does the hose end? Vacuum hose for fuel flow? I dont think it would even start. Is the fuel tank below the carb or above it? I have no idea what model you have, plus the only Piaggio I know is my Liberty 150 and it has EFI. Im wondering if you could be getting vapor lock. Next time the scooter dies out, quickly loosen the gas cap and see if it 1: Makes a hiss noise. and 2: Starts right back up after the cap has been opened. I had a old car that did vapor lock at random. Annoying and embarrassing. I just drilled a tiny hole in the top of the fuel cap. You could also do a plug chop when it dies and see if its lean. White colored end is a lean sign, it should be coffee colored. I dont think thats the issue though.

Looking better at the picture you posted I think its just a fuel spill hose. Makes sure the fuel goes to the ground and not onto something hot.

Just remembered, but this is probably is not a cause. About 3 months ago I put some hardware on the back of the scoot so I could hang grocery bags and drilled one hole into the gas tank, 3/16". Didn't know it, had gas coming out for about a week, Duh, did smell gas but scooter ran fine. Finally repaired the hole with JB weld, then ran fine for several months. Several days ago I drained the tank, pulled the petcock with a very good condition filter attached, and it was totally clean, no way anything could have gotten through that filter. But perhaps it did and is now in the carb?? But I still don't see why there isn't a continuous problem from any tank or carb issue? And how it runs great when cool.

So did you try all the other suggestions? If so, you might have pinched a fuel line. I pinched one on a Genuine Buddy and it would only get pinched when riding/sitting on it. It would stall, you would get off it, then it would mysteriously restart like nothing happened then repeat all over again. It got narrowed down and solved quickly because it started right after putting it back together. To rule out the overheating suspicion I would get a CHT gauge for the spark plug and get the operating temps in real time.

can you give an example of a gauge online? Hook it to what? Amazon has a Trial Tech TTO CHT sensor for $50? It's $110 for the shop to check it out scheduled tomorrow. I'm right now cleaning the jets on my carb. Checked the repair on the tank, its holding perfect.

So decided not to remove carb after consulting several shops. But I did call ScooterWest.com and after telling me "Dude, shut up and listen"LOL, I was told that the Piaggio Typhoons all come with a charcoal cannister for CA EPA emission standards and that many have the same problem as myself due to overfilling the tank and the cannister causes vapor lock in the carb float. He said to remove the cannister, or put holes in it and I spoke to the shop that I'm taking it to tomorrow about that and they said its possible and they would remove it for me if that was the issue. While I'm swallowing my Doityourself Scootdawg pride by taking it to a shop for the first time since being a proud member, I admit defeat! Chinese scoots are much easier, yet I don't miss my Quinqui 50cc, cause I was working on it all the time. My Piaggio never ran better than today with the new plug, rollers etc.(that I did myself) but this fuel issue is a real stumper!!

I've yet to overfill a scooter to the point were the fuel goes into the emission canister. I know Piaggio BV350's are prone to that issue and I believe my LIberty 150 is prone to as well. Now the way I understand it is the fuel will burn off and everything will be back to normal after a few miles. Im not testing this theory on my Liberty! Trail Tech is the CHT reader I use. You remove the ring from the spark plug then slip the CHT ring base around the spark plug and mount the gauge to a place you can watch it. Order a extension cord for it, stock one is short. My CHT ring finally broke and replacements are overpriced, plus I sold my last 2 stroke so I no longer need it. Great item to have on hand for trouble shooting so I guess I have to order extra rings though. Still wondering why you even had transmission issues at such low miles to begin with. Post your solution when you get it.

Actually, the "slipping" I believe was the beginning of the fuel flow problem because I noticed it at the very end of a long ride. I'm 99% sure that it is a vapor lock problem due to that charcoal filter under the tank, but hopefully today I'll find out. Really appreciate your support, info and advice!!