Currently, I have a 39MM on it, but the bolt on the bottom of the carb stripped out. Not the nut part that holds the bottom piece on but the actual piece that it screws on to. Anyway I was thinking about just buying a whole new carb. The mechanic said get rid of that piece of junk 39MM carb I have on there. So..., what size should I get?

 

First, what size cylinder are you running? If you are still stock, the original carb was a 34MM. I would certainly not run a 39 on a stock cylinder. I've ran the 38MM Keihin Airstryker carb on 2 different 310 kits and it's a great carb for a big bore. It would be OK for a stock cylinder but you will loose some bottom end punch. For a stock cylinder a good setup would be a 36mm and with a big bore setup I'd go with a 38mm.

 

I think your talking about the drain screw (bowl screw) Your talking about the screw on the very bottom of it and when you take it off you can see the main jet right there right? If the screw is striped Im sure you can get another one. If the threads where it screws into is striped I wouldnt bother and get a new carb.

 

Yeah its the main drain swrew. What ever it is that that screw/bolt screws on to is stripped. Is that the main jet? I was thinking about going with the 36mm. I'm pretty sure its the stock bore.

 

No that screw is not the main jet, but when you take it off that little gold thing with the hole in the middle is. Yes the 36mm would benifit you with a stock cylinder. 39mm is overkill.

 

Cool, thanks. Think I'm just gonna buy a new one.

 

Don't buy a new carb, just see if you can buy the new bowl for the bottom of it. I would check with ESR, if they don't have it try going through Keihin/Sudco. Yes for a stock 250 the 39 is overbore, but not overly so. I use a 38 A/S on a small bore engine and like it. There are many people out there that use 40.5 Keihin's on factory cylinder bikes. If you switch back to a smaller carb, you'll have to buy more than just a carb. You may have to buy a cable, intake, airbox boot, and all the other little headaches that come with it. Bottom line: The 39 Keihin is a good carb, it just needs to have more motor behind it.

Nic