Hi Brad. Doesn't sound like much fun. The air screw adjusts the amount of air bleeding into the riser for the main jet, turning the fuel going up toward the carb throat into a foam. This makes it vaporise more effectively and mix better. Letting more air in will lean the mix up a little, but it's not as good as putting in a smaller main jet. If you can break the seal, turn the air screw carefully inwards COUNTING HOW MANY TURNS until it's gently seated. It's usually something like 1.5 turns. You need to know so you can re-set it. Then back it out to where is was and then try another half turn further out. I would guess that any more than 1 complete turn out from normal would be the most that will still let the motor run OK.

Have you been into a carb before? If not I'm sure there are lots of pictorial guides on the net. It's easy to replace a main jet. They are usually either the sort that are buried inside the riser and you need a correctly sized, well fitting screw-driver to get them out, or are the more external hex-headed sort that you need a 6mm (about) spanner to undo. There will be a number on it, something like 122.5 or 140 etc (the numbers on most carbs go up in 2.5 increments). Find what number is on your mainjet and buy the next two sizes down. IT"S A BAD THING TO USE TOO SMALL A MAIN JET FOR THE CONDITIONS! You can over-heat and seize the engine running too lean for too long. Fuel going into the motor and vaporising has a big impact on the internal cooling, especially to the piston. Try one size smaller before deciding on going two sizes smaller. It's a bit hit and miss, but that's how it is with carbs. Be very sure to replace the original main jet as soon as you get to lower altitudes. If you know that you are going to head up again and don't want to keep replacing the main jet all the time, it's OK to run with a smaller main for a while as long as you keep the throttle at less than 60%. The restriction of the main jet size on fueling doesn't come into play until you are getting close to wide open.

Hope this helps.

Kind regards

Nigel in NZ

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