I have a keihin PWK 39 mm. does anyone know how many turns out you can go on the air screw before you have problems...my quad wants it way out. I have an 88 trx 250r ported and polished with an fmf pipe. thanks for the help.

 

It all depends on your pilot jet size, needle tapor and fuel mix ratio. Just set it to where you have a nice idle with a little smoke when you blip the throttle. Should sound like a chainsaw on steroids

 

If you need to go more than about 3 turns out, then you probably need to lean out your pilot jet and/or needle.

Adjust the air screw by listening to engine rpm. Higher rpm means you are adjusting it in the right direction. I usually find where the engine runs at the highest rpm and then turn the air screw back in about 1/2 turn (for two stroke motors). This way it'll be just a tad rich and safe.

If you end up with your air screw set to between 1 and 3 turns out, then you're ok. If it needs adjusting beyond those limits, then either jets need to be changed, or there is another problem, like an air leak, or float level issue.