Modern Vespa

Hey all,

Look for some input here.

Vespa t5 with pinasco master cases. Polini 152 cylinder, stock 24g carb and sito plus exhaust.

Jetting is 120 be4 125
Pilot is 50-100.
Mix screw out 3 turns on a fine thread mix screw.

B8 plug.

My issue is that the bike fires up and it idles with the choke open. Once I close the choke, it dies instantly.

It wont fire or run with the choke closed.

Im currently in the process of cleaning the carb and jets and replacing all carb gaskets.

Aside from a massive air leak, what could I be missing?

Any assistance or suggestions are always appreciated.
Thank you!

N

Check the following:

1. Clogged idle (pilot) circuit
2. Air leak (carb base, gaskets, intake)
3. Float/needle issue

It's either the tiny hole in the end of the pilot jet is blocked. Or oil seal failure. Nothing much in the middle.

Thanks guys.

The pilot jet is cleaned and will be reinstalled.
Ill swap the float needle for good measure even though it's a brand new carb.

Go from there.

Thanks again.

N

So here's an update:

After a ton of trouble shooting (with plenty of help) ive established thay i belive the carb itself is causing the poor idle issues.

I swapped the carb box and csrb to a p2 carb box and 24e carb with stock p2 jetting snd a 125 mj. The bike idled fine.

I refit the 24g carb in the p2 box and it again, idled like shit. Died when pushed in the choke.

Jetting for the 24g carb is as follows:
120 be3 125 pilot 50/100.

Should I consider changing some jets? Different Pilot?

Or should I just slap on the 24e carb and be done with it?

Let me know. Ideally I woukd rather run the bike with the 24g carb but I am tired of chasing gremlins.

Note: the timing is at 16 degrees btdc so I will have to adjust that back to 18.

Any Intel is appreciated.
Thank you

N

At least its minor. That's something. T5 runs better with a G carb. Could be blocked in the pilot circuit but more likely the idle jet itself. The end hole blocks easily and sometimes ultrasonic cleaning won't shift it. When really blocked it has to be poked with something stiff.

Same here. The G carb is 1cm lower, and its architecture is designed to complement the "square" architecture of the engine, which is why these engines are revvy instead of torquey.

Stick to the G carb if possible.

I had the same issue at one point (on a T5, incidentally): it would run fine through the gears, but would die as soon as I stopped at a red light. I'd start again and stall at the next red light. A buddy who was riding with me suggested blowing air into the idle jet, and it worked ....for a while, then stalled again after a mile of city traffic. I think I had to stop 3 times on the way home just to make it there. I then thoroughly cleaned the carb and reassembled it, and that was the last time it gave me any trouble.
Must have been some junk in the pilot circuit that kept detaching and blocking the jet; and as Jack said, it could take a hard brush bristle to unblock it.