Modern Vespa

My P seeps from the carb a bit (not to death, just more than I'd like). Cases often have gas dripping down them just along the back towards the rear shock mount after a 30 min ride or so.

Thoughts on shutting that down? Carb's on there solidly. Just still getting a seeping.

Been told it's normal. Rather just fix it.

Check to see if the gas spigot on the carb is weeping. Then check the float needle. The needle is cheap, just a dollar or so. The rubber tip should be soft and rubberry, sometimes they get hard and a groove develops where it seats and it'll cause to much gas in your float chamber which will eventually seep out.

There is also supposed to be a rubber plug covering the idle mix screw at the back of the carb box. If the bike is flooding then it's best to just leave this out so the carb box doesn't fill with gas. But when it's missing (even if all is well) it will always drip a bit from the back.

yep, this is true

if you removve the cowl and carb lid, plus the air flter

run the bike and you will probably notice the carb will belch back fuel

the mechanics of exactly why this happens are unknown to me

i will say that it seemed normal to me when i finally witnessed it

i run a big big jet

and will also say that this belching stopped when i replaced the stock crank with the mazzy that 's in it now

so maybe the belching is due to the different draw times of the cuts

just guessing

Scooters will always belch, they are just rude like that, also called spit-back. It happens when the air/fuel rushing into the engine suddenly finds it can't get in as some jerk has closed the rotary valve. The crowd piles up and then starts a stampede back out through the top of the carb. Given the top of the carb is a squared off edge they spill out around the top in a vary disorderly fashion causing much of the air/fuel waste so much energy that they just can't bring themselves to make another run at getting into the engine. Instead they just fall exhausted to the bottom of the carb box.

The rounded edge of the vortex carb improves this situation greatly. Most proper carbs have a nice bellmouth at the entrance. I really should get back to work on that bellmouth intake for the p125x.

Bike's not really flooding... though you do mention the needle, and that was a thought I had at one point last time I rebuilt the carb...

I'll check for the plug near the idle mix too.

Just to be clear, the plug covers the idle mix screw. ie to adjust the idle mix you pop the plug out, then when you are done you put the plug back. So if you can adjust the idle mix then the plug is not there.

The other natural place for fuel to run down the back of the cases from in the float bowl overflow vent which exits the airbox just behind where the fuel line enters the air box. Bumpy roads make for more dripage.

if it starts easily and runs well, your carb is probably fine, like others have said, it's not unusual to have a little dripping here and there. If you are getting a puddle, replace the needle, float and fuel tap (one at a time, in that order).

Note that all needles are not created exactly equal in length. When you take off the top of the carb, hold it upside down and note the position of the float arm in relation to the top. The float arm should be level for both the old and new needle. The needle length affects the float height, which in turn affects the mixture (low float = lean, high float = rich). This affects Vespas more than most small engines.

Cheers and good luck,
Bob

Try replacing the gaskets, one between the carb and the air box, and the other between the air box and the block... worked for me.