Modern Vespa

Ive pulled the tank/carb/tap, and cleaned it all. Spark is good.

To start: key on->fuel on->enrichener out-> 2 kicks and it starts. Runs like a top.


15 minutes later it stalls at stop lights. Seems like its emptying the float bowl at idle, OR possibly leaking fuel into the carb.

I have to pull over and pull everyrhing apart. Sometimes the brass fuel sprayer tube is dripping fuel into the carb, other times not. Cant seem to figure it out. Only really happens in the morning on its first startup. Is it a leaky fuel tap?

Any ideas?

If the float needle and seat are in good order it should run without a fuel tap.

ok, I think i recreated the problem.

I got it started and let it idle. It eventually died after a minute or so. I turned the fuel tap off, and removed the top of the float bowl. The fuel was at the bottom of the bowl. If im thinking correctly, the bowl isnt staying full with the tap on, but im not sure where to look. Everything is new/clean.

Update:

Drilled the float bowl on my original 20/20, and installed it. Started up, and idled fine. Going to jet it an run it.

I'm not sure how low fuel level in the bowl equates to enlarging the passage to the well....Thousand upon thousands of these motors run fine with the stock hole size.

It doesnt. The scooter has a malossi kit, and the carb i drilled was the original, not the one with the low fuel issue.

I think you are wise to put the 26.26 aside and just use the 20.20. That is what the Malossi 177 was designed to work with. I would follow Malossi's jetting instructions too. Use the 52/140 idle jet that comes with the kit. Start with an AC140/BE4/MJ115 main stack. If I read your prior posts correctly, you opened up the case a bit but did not cut the crank. In that case, the MJ115 might be a little rich. Give it the old WOT in 2d splutter test and find out.

So it turns out the threads for the mixture screw on the 20/20 are buggered, so thats that. BUT, it did idle continuously without dying.
I had noticed that the float needle on the 20/20 was spring loaded so I pulled the float assembly from the 20/20, and put it in the 26/26. Bike started right up and got me around for a bit without a problem. Took it on a long run in 4th gear, hit a stop light, and it died a minute later. Took about 5 kicks to restart, died a minute later, restart, etc.

It literally dies at the same exact stoplight every time. Its after a mile of 4th gear riding.

Could it by any chance be a clogged gas cap vent?

That is possible. Easy enough to check. Just loosen the gas cap and ride. Obviously better not to do that when the tank is completely full.

Also, the fuller the tank, the sooner it quits.

If it dies faster with a full tank(more fuel pressure available) I would suspect the float needle and seat. If you run Ethanol gas, it probably ruined the rubber tip or your float needle seat has debris in the needle seat bore that is not letting the rubber seat seal off the fuel flow when the float is raised. Check the float too and make sure it isn't cracked and partially filled with fuel.
Also look at the fuel tap vent tube inside the tank. Make sure it's always above the fuel level.

Good luck!

Hec

Picked up a new 20/20 today, drilled the floatbowl, and it runs fine. Rich, but fine.

Good news.

So glad you can ride. We are having a good old-fashioned New England winter here. With the subfreezing temps, the snow, the ice, and the salty roads, I'm not scootering anywhere any time soon. Have a couple of off-season projects pending, but too cold right now to even tinker in the garage.

Ahem. It's -4F as I write this at 8 pm! We are on the way to a low of -18F tonight. My scoot is inside!

Hec

Trying to rejet now that i replaced the carb with a 20/20.

140/be4/118

Feels pretty good, but i think it ran the bowl dry on a 4th gear .5mile stint. Engine just cut off.

The carb is new and the jetting is in the ballpark. Something else is going on. If it's fuel, it's upstream of the carb--tap, fuel line, gas cap. But, as the saying goes, 90% of carb problems are electrical, so you have to consider the possibility of some kind of intermittent ignition fault too. Does this scoot have points or a CDI?

Its got points. Maybe the previous mech didnt return it to 19*btdc. The 26/26 jetting (120/be4/122) ran like compete ass on the 20/20, so i took a guess with the 140/be4/118. Maybe i didnt get the float bowl passage opened quite enough…

If timing was wrong it wouldn't be intermittent. Drilled float bowl is not an issue with an MJ118. Most likely cause is an intermittent short in the kill switch wire. That will only get worse. On a Stella, you can test that by disconnecting the kill switch wire where it connects to a junction block under the horncast. Not familiar with the setup on a P125X.

I figured that much about the timing. Its a beautiful day out right now, so im gonna go for a little ride and see what happens.

Shouldn't your timing be around 21 +/- 1 degrees if it has points and 18 degrees if it has Electronic Ignition? My VMC 177 build has points and 22 degrees was recommended by folks here. My Haynes manual says the same thing! Looks like you will need to get the degree wheel out and have a check to see what your timing is set at.

Hec

Mystery solved. Ran out of gas.

Dooohhhh!