Modern Vespa

Hello all I'm new to the site. Need a little help here I'm going crazy. Just bought this 1980 vespa p200. Had bad gas so I cleaned the tank out, put a new fuel tap and rebuild the carb and new lines. It starts but when I give it gas it acts up and starts bogging up and down. I'm at a lose. I've tried different spark plug, spark plug wire, coil also tried feeding fuel straight to the carb to eliminate the fuel tap. Please assist me I'm going crazy.

Last edited by Napolikidd on Sun Oct 31, 2021 12:54 pm; edited 1 time in total

I can't get the video to upload. Put it on you tube see link.

https://youtube.com/shorts/nj-1s3xcTHc?feature=share

Welcome!

First of all, I can't make sense of the engine sound in the video because you are revving it a bunch. We need to hear it just idling on its own, and maybe then held open steady at a certain throttle position, or a single opening of the throttle from true idle to wide open, to get a sense for if something sounds wrong (hitches, gurgles, etc)

Second, I noticed your autolube hose is disconnected. Unless it has formally been converted to a premix bike, connect that thing up, put oil in the autolube tank, and stop running and revving it until you do!

Lastly, the general symptom of a scoot bogging when you open the throttle our often an air leak (too lean), but I think there's not enough info to go on yet. Is everything stock?

Hope this I better.


https://youtube.com/shorts/VE9MzjGsV5A?feature=share

Have you been messing around with the carburator at all? the last time that I had that issue it ended up being my fuel line coming from the fuel tank pinched under the seat and also a bizarre and rare mistake made by my mechanic putting the wrong size studs on the engine case and the carburator hollow nuts wouldn't seal the carburator box into the engine case causing something similar to that.

I would personally remove the carburator, pull every jet and look at the gaskets again and retighten.

All new gaskets

Last edited by Napolikidd on Sun Oct 31, 2021 4:32 pm; edited 1 time in total

I just rebuild the carburetor and replace all the gasket to the base of the air box and the carb to air box. I have taken the carb off 3 times and inspected it and place it back on and same thing goes on.

The stock gasket between the carb box and the intake is VERY thin. If there is even a little pitting or warp in the carb box, it will leak. Maybe get some marginally thicker gasket material and make your self a copy? It worked for mine.

Lightly greasing the gaskets can also help, it'll kill any small leaks without making things impossible to get apart cleanly later.

From the sounds of that motor, if the carb was leaking, fuel will roll down the back onto the floor. Is that happening?

Can you provide some more history of the bike? Was the bike sounding like that before the carb build? What made you rebuild the carb? Will the bike rev high if you turn the idle screw all the way in? Did you remove the flywheel or anything else on the bike before, after, or during the carb rebuild.

Maybe a passage way in the carb is stuck somewhere. How detail was the carb rebuild? Did you remove everything from carb and blew carb cleaner and air through every hole? What are the air mixture and idle screws settings?

Fuel is not leaking.
I rebuild the carb because two week ago I received the vespa and it had a tank full of bad gas. So I cleaned the tank change the fuel
Tap and cleaned the carb.
The guy I got it from said it was running not to long ago.
I did not remove anything else on the bike.

I did completely take the carb apart and blew through all passages. The air fuel is seat at 1 and a half turned out from all the way in and the idle screw is set to were the slide is just barley open.

Are you pre-mixing 2t oil into the gas? Because while the oil line is hooked up, it looks like it's still empty.

Also, it looks like there's no spitback out of the carb at all when you rev it. There shouldn't be a ton, but there should be some. That makes me think fuel starvation, so something is not flowing right through to the jet stack?

Alternately, it could always be electrical...

No it has an oil tank which I replace also. The line is full may be the video it doesn't look like it but its flowing. And there is spit back with the gas. Like right now I have it running and it idling perfect just get weird when I give it gas.

Clutch seal is a great place to have an air leak

And a terrible place to have to fix one.

Drain the crank case oil and see if it's watery and smells like gasoline. If so, you're splitting the cases and your journey is just beginning.

If you have a pressure test setup, you can confirm it's the clutch side seal because you can feel the pressure at the oil breather, too.