Understanding Main jet?

I got a 1980 xs650, and before I start working on the carb I want to clear up something that i've been wondering. I know that with jets, they're very specific and are based on turns. As in how many turn out.

But what i'm wondering, is for the main jet, you don't adjust it by turns right? you just increase the main jet screw size? My main jet screw says 135 on it, and from what i';ve found, i just screw it in. I don't have to worry about screwing it to a specific tightness or anything right?

from what I've learned you don't adjust any off the jets, only change size. the one you adjust is the idle screw and the air bleed/mixture screw.But I might be wrong...

Originally Posted by perezmaximus

from what I've learned you don't adjust any off the jets, only change size. the one you adjust is the idle screw and the air bleed/mixture screw.But I might be wrong...

You are right on these carburetors. The jets tightened up. There is no adjustment for them. The fuel mixture screw, idle, float level and needle position are the adjustable parts of a stock xs car.

Here's the carb guide:

http://www.amckayltd.com/carbguide.pdf

Thing is, your bike should have come with the the BS34s seeing as it's an 80, but if you found a main jet that's a 135 and the carbs haven't appeared to be rebuilt, I'd suspect you have 78-79 BS38s.