Bonneville America Forums Forums Technical Forums Performance Mods Idle Mixture Thumb Screw

Just got the idle mixture thumb screws from Brent. Can anyone tell me from experience if I screw these all the way in tight & back out from there? Do I just screw them in until I feel it snug & stop? When I screw them in until I feel it snug & back out 3 turns they feel loose like they will vibrate out

You should never screw a mixture screw in tight, you will damage the tip of the screw and the seat. They should just lightly seat then turn them back out. Don't just go back out 3 turns, you need to adjust them the right way. As far as being loose , they shouldn't be as loose as you seem to be describing. Did you put the washer,O ring , and spring on them?

The bike runs good. I went 3 turns out because that seems to be the best reference point based on what I have heard. I have D&D pipes & 130 main jets, AI removed. If I went 2 turns out would it make a big difference? It looked like an awful lot of screw was exposed & it could be wiggled from side to side. Just trying to be cautious.

Better to err on the side of caution. Those screws are not 100% the same as the stock screws so the best thing to do is adjust the right way. If they seem too loose and you are worried but need 3 turns out you can always put a larger pilot jet in and then you won't have to turn the screws out as far.

If you have the washer, spring, and o-ring in there properly, then you need to adjust them based on popping on decelleration. Start at one turn out (as mentioned "lightly" seat them) and adjust from there. You want to end up with a slight gurgle on decell, not a loud pop. If you get to 3 1/2 turns out before that happens, you need to step your pilot jets up and start over again. You can still get a pop if you have an exhaust leak (sucks air), so make sure your manifold nuts are tight and the header to pipe and crossover connections are tight. The thumb screws will seem loose because you now have a lot of mass - the knurled thumbwheel part - hanging under the carb, but if you have the spring, o-ring, etc. in the right order and seated properly they won't fall out.

The decel pooping is only an indication, the right mix is what you are looking for. You basicly adjust for best idle. I disconnect the lkeft plug to adjust the right cyl. and vise versa. Turn the screw in until it runs rough then out until it runs rough and the correct setting about 1/2 way between the 2.

Got it. Thanks guys!