Modern Vespa

Rebuilt the carb on a P200 that I'm fixing up. Put it back on, checked the throttle, carb sticks at WOT. I swapped it with another I have that slides just fine on the bench. Once I put the second one on the bike, it gets a sticky slide, not at WOT, but more in the middle... If I loosen up the forward carb bolt, the stickiness goes away. I had torqued the bolts to spec, and the gasket is fine (did not put a new one in though).

So, if the slide slides easily off the bike, but sticks when mounted, is the carb box warped? Can that happen? Is it ok to run it with the front bolt looser? I've searched for this on the forum and it seems some say that is the remedy. I was wondering about the carb box though...

Two quick ideas:1) take the carb off and rest on a piece of glass or something flat and see it you can rock it a little. You can shave the body a tiny amount with sand paper on a flat surface. 2) check the carb box . If it's not flat, that will mess you up too. Good gasket underneath the box and tighten down properly. Use some blue locktite on the screw or will wiggle loose.

Here's a question, though -- how to check the flatness of the *inside* of the air box? Presumably, if you've warped a carb in the box, you've probably also somewhat warped the floor of that box as well.

I've done this.....you overtightened the bolts. The fix I found was filing down the inside of the carb body where the throttle slide goes so the slide can move freely again.....if you have been thinking about replacing your carb I would say go ahead and do so but it can be fixed.

Seems a common problem. These are both project bikes I'm working to get running, have not ridden either... Both carbs I've been working with (hoping there was one that would work) seem to be warped. I figured I'd concentrate on one, assess the results, and then decide on whether or not to replace the other.

I lapped the bottom with 220 grit and WD40 on a piece of glass, then filed out the slide channels. That got the slide moving nicely. It stayed moving when I replaced it in the bike and torqued it to spec. Have to finish de-coking the head and I'll get it started and see what happens. Thanks again to everyone for sharing their experience!!