I’ve tried everything on earth to get my pre-evo engine to idle and it won’t, so don’t let that alarm you. I’ve gone to the point of reaching out to dellorto themselves and they said they believe the fuel pump is simply too strong at idle (supplying too much fuel) and thats why they don’t idle. If you are not limited by rules you can lean the idle jet very slightly and see if it helps but becareful…too lean and you risk the engine running too lean on overrun and seizing the piston.
Compressed air and brake cleaner are both a must when cleaning the carb. You need to get an air nozzle with an extended fine tip so you can blow through all the small ports (and there are many).
Set the float height to 3mm measure from float arm to base of carb (no gasket) by bending the upper middle tab that sits on the check valve. that check valve is also something good to replace if you have never done so.
If you have a 12.5 venturi carb you should be using the 5.2g floats and 30/30 idle jet and idle emulsion tube. If you have the 8.5 venturi carb you should be using the 3.6g floats and 60/60 idle jet and idle emulsion tube.
Wind the throttle stop screw all the way in and back out half a turn if it does nothing as you’ve already said.
To set the air screw, get the engine fully warm and up to operating temp, then get a buddy to help you out. One of you operate the throttle with your hand and very very slightly give the least amount of throttle you can to keep the engine ticking over. Once you find that point hold it there and ensure you do not move your hand. The other guy can now unwind the air screw quarter turn at a time from half in and you should hear the engine start accelerating even though the other guys hand is constant on the throttle. Keep winding the air screw out quarter turn at a time until the engine stops climbing rpm, this is your set point. Usually the point is 1.5-2.5 turns from fully in depending on your atmospheric conditions…do not go more than 3 turns out.
Main jet as Marin already said, keep going one leaner until it pops with your foot down all the way, then go back up one maybe two until it revs cleanly to 13000+ rpm. The needle clip on a pre-evo is almost always either on clip 1 or 2…you need to feel the response of the engine when you first press the gas off a corner…its the same as the main jet…it feels better the leaner u go but too lean and you’d reach a point you go full throttle out of a corner and the engine gives no response…just hesitates as if you never pressed the throttle and then suddenly springs to life a second or two later…go back one clip richer on the needle.
If you need any futher help with the engine feel free to post and I’ll do my best to help you out.