Modern Vespa

I took apart my carb to clean it and found that the jet was the standard 116 size. According to Scooterworks you should re-jet your carb possibly 125 or 130. I live in Sacramento elevation 300'. I also found that the mixing jet was out about 3-1/2 turns out. This seems excessive. I put it back together and adjusted it out 1-3/4 turns out and had to turn up the idle. It ran okay but it sometimes would be slow returning to idle speed a few times. I'm going to check the plug after it cools down later. Anyone have experience with this?

For just a pipe, 2-4 points up is standard. 116 is the stock jet for a 24/24 carb. I would recommend a 118 or 120. I'm not familiar with the Prima pipes as we don't sell them. A 125 or 130 would be way too rich.

As for your air/fuel mixture screw, just rotate it back and forth slowly until you get the cleanest and highest idle speed. Then adjust your idle speed accordingly. There are new carbs with mixture screws that have a finer thread on them, meaning that it will require more turns out to run properly.

Thanks for the advice Max.

I recently bought a new carb and now the mixture screw sticks out of the airbox and the rubber grommet will not fit on the hole. Is there a different screw cover available?

I'm not sure. I also have the same longer mixing jet and I found that I had to remove it in order to get the carb out and back in. It didn't have a rubber grommet on it. You might try the one on the Idle screw to see if it will fit.

They all come like that now. Those are the new carbs with the longer air/fuel mixture screw that has the finer pitch threads. Those need like 3-4 turns out. We modify the screws before we ship the carbs out by shortening them and cutting a groove in them so you can use a flat head screwdriver to turn them. I guess other shops aren't doing that. It's an easy process to do. There should be a grommet on the back of the airbox to cover the hole.