Modern Vespa

Geez! I've had my 1966 SS180 US spec. Vespa for 35 years, and just when ya think you've seen EVERY problem, something weird pops up. It's a combination of backfiring, and the engine quitting. VERY random. I might be sitting at a stop light, idling fine, smooth, then it just shuts off. Sometimes, it will backfire as it does, other times not. I push it to the side of the road, kick - nothing, kick - nothing. At some point in many kicks, or sometimes with just one kick, it will backfire, then the next kick, it starts right up. It runs down the road perfectly. The spark and the spark plug look great, hot or cold. The back fire is only through the exhaust as far as I know. I've drained the fuel and replaced it with known good fuel - three times. Carburetor is spot on. If I go out for a ride, say, to a store, 2-3 miles, it will quit at least twice. I can't predict it at all, other than it never quits at speed. Suggestions please!
- Paul, USA

What kind of ignition you have?

My bet would be a timing issue...
Check your points gap if you haven't converted to EI.
Check your timing with a strobe if you are on electronic.

I remember the first few times i started my 180ss many years ago. The condenser on the stator started to act up and backfire...sounded like a gunshot! Haha. Changed condenser and all was good.
Fab

I have the original type points and condenser system. It works well. I have had condenser issues over the years, usually down to poor quality aftermarket units. EFFE units especially. NOS ICET ones from Ebay seems to last the longest. I didn't lean towards the condenser because my experience with a failing condenser is usually manifest with very hard starting and/or breaking up at speed. I'll give it a try!
- Paul

what's interesting is you can add another condenser in line anywhere along the ignition/kill to test.

Also check the woodruff key. Sometimes they got sliced in two...

Try a known good coil.

It was the condenser. 100 Cool Points to Chef!

It seems like a failed/failing condenser can be the cause of any particular symptom! My SS was running fantastic down the road, but with random cutting out at idle or slow riding, but with a observed great spark and a very nice spark plug condition. So a bad condenser can give a great plug, or a fouled plug; poor running at speed, or great running at speed; hard starting or fine starting. CRAZY!
Thanks for the help group!
- Paul B. USA