Modern Vespa

I've been getting my much neglected '76 Rally on the road and before I started on it the scoot would only run with the choke on. I'd turn off the choke and it would run for about 30 seconds or so and it would die. When I did run it with the choke on it would also try to die when I gave it full throttle. Not good all around.

So I rebuilt the carb with a new seal kit, re-jetted for the Sito Plus (up on the main from 116 to 118) and a fresh battery and guess what?

Same thing

Starts with the choke on and runs for a bit when the choke is off.

So now where do I go from here? Engine timing, air leak, small hole in the piston, I'm open for suggestions.

By the way it's an early oil injected Rally w/ 6 volt Femsatronic ignition.

what does your spark plug look like?

Check your gear oil. Does it smell like gas?

jamesjohn the plug still looks new. I only ran it for 15-20 minutes this afternoon after I put it all together. It was a new B7ES by the way.

I'll take a look at the oil tomorrow and see if it smells like gas. What would that tell me?

Hey Mark,

Check out this old thread, which sounds a little like what you're dealing with. Might be a clutchside seal.

Thanks, I'll take a look at the seals this weekend.

Sounds like possibly a clogged up carb. When you get off the choke/idle circuit it dies since it is crudded up and can't deliver gas.

Thanks SF bit I don't think it's a carb issue as I disassembled the carb and soaked the parts in solvent overnight and used a new seal kit. And I blew compressed air through the orifices before putting everything back together.

It's sounding like bad seals to me and I'll be following up on it this weekend

Look at the little round rubber that goes between the carb and the carb box,
Mine would tick over but would die when revved. The rubber was solid put another softer one in and it ran like a dream,Hope this help's.

Huh? That rubber piece is just a bush between two places that touch. No air or fuel or anything is affected by replacing it with new.

I know but it prevented the carb from pulling down on the gasket so therefore sucking in too much air.

Then the carburetor sealing surface is uneven or the box is warped.

No its not as done the glass test,Put the carb and box on a sheet of glass and all surfaces were perfectly flat so it couldn't be the problem!!

What Chris is saying is it's warped when bolted down. It might look flat when you rub it on the glass, but when you torque those bolts down, it's so easy to warp the box.

I know, 'cause I've done it.