Modern Vespa

Hello everybody!

My name is Kamil.

I have a problem with my Piaggio fly 125 2005, engine code m421- milage ~14k kilometers.

The engine starts and heat up perfectly, problem is with low power/low rpm, he can't hit more speed than 40km/h. On stand looks like everything goes right - engine hits low/middle rpm's slighly but not on the road.

What i done:
1. I cleaned carburettor (KEIHIN CVEK26), flow screw - turned twice from the close position. Also replaced vacuum valve to factory new (somebody can tell me how it work /should works?)
2. Changed to new one: fuel supply pipe, fuel valve low-pressure pipe, SAS pipe, air filter, spark plug - claerance 0.8mm
3. I set up claerance on valves in head : intake 0.10, outlet 0.15
4. I sealed air filter box with new bands - engine not respond for autostart spray.
5. Sometimes when I rev engine, it shoots in to exhaust system
6. I haven't looked yet under transmission cover - maybe here is a problem ?

Here is my video - maybe you'll catch something that I missed.

https://youtube.com/shorts/FKy-hHkrDYM?feature=share

Check the engine compression.

Done, ~9,8 bar on guage.

I looked up behind cover, everything looks ok but transmission belt has cracks on tooth's i need to replace him. Belt had numbers - Dayco 22,5x814 LE 8118K 09033186 - is that right for my engine ?

Another update

I found crack on rubber manifold witch connect carburettor with cylinder.
I replaced it to new one, urfontunately did not help.

Now im in critical point, i have no idea what else to do.

The engine seems like it is revving freely enough. Have you taken a look at the belt/rollers/clutch?

Yep, everything looks good, but belt need's replacement. I can see crack between tooths on them.

My problem is solved.

I filled up can with 3liters cold water, add 100ml multipourpose cleaner called "DIMER" in Poland, and throw the carburettor into this mixture.

After 3 days, carburettor was taken out from can, cleaned with compressed air. Then i put together all parts of carb. I set it up into rubber manifold and voilà ! it's works perfectly.

During assemble carb i meet one problem - the rubber of the vacuum valve does not fit well with the seat, its taken me a few minutes for it to sit well and it worked.

I think it's of problem with some dirt in carb or bad fitment with rubber from vacuum valve - now engine works great and again give fun on ride the scooter

Thanks for all Users to tryed help me. Cheers!

Last edited by Donik on Sat, 14 May 2022 20:38:50 +0000; edited 1 time

Well done