Modern Vespa

Hi Folks,

I replaced the exploded original engine on my VGLA1T with a modern LML. It ran well for a while then started to act like it had a rev limiter, bogging down and backfiring under any throttle much higher than idle. I have rebuilt the carb, same thing occurs. Bike idles great.

I am looking for advice on where to start trouble shooting. Timing? Jets (all factory currently)? I do have the original exhaust on as the LML one wouldn't fit on the bike. Could that be an issue?

Any sage advice is appreciated. I am going to borrow a friends timing light and check that tonight.

Mark
Regina, Saskatchewan, Canada

Sounds like an electrical problem. Maybe the pick up is gone wonky

that was my first thought as well.

I'd be chasing ignition and/or wiring before jumping back into the fuel system again.

No changes were made between the running great phase to the bogging phase?
When you cleaned out the carb did you find any dirt or grime?

I had mine a few year ago with the exact same symptom - it was an electrical problem.
Replaced contact breaker and condenser - problem solved

CDI

Thanks All,

Carb rebuild didn't show any excessive grime. Carb was fully rebuilt and ultrasonic cleaned. It does appear to be more of an electrical issue at higher RPMs. The problem appeared after a cold winter but the bike was never below -10C. I am using new fuel.

I plan on unplugging all of the bike electricals from the Regulator plus remove the kill switch wire to the CDI to eliminate that as an issue, troubleshoot the CDI/Ignition (spark plug wire, measure resistances, check plug, etc.). Will also check the exhaust if none of that yields a culprit. Will update the post as it's always good to find a similar problem and solution!

I may be back with dumb questions if I can't find an answer somewhere...

Cheers

Mark

p.s. It is +6C today. The riders are showing up despite the snow and ice on the side streets. Soon!

Update (very delayed): Thanks for all the help! It ended up being the wiring in the flywheel. Replaced and enjoyed a season of care free riding except when it was running too lean and the scoot tried to rev to infinity and wouldn't shut off as it was basically 'dieseling' and didn't need no spark to run. Holy shit. I stalled the bike to stop it. Lesson learned.

Thanks for all the help! -28C today (-40 with the wind chill) so plenty of time left to dream about Spring rides

Safe travels,

Bud

Regina, Saskatchewan, Canada