I had a bone stock 1986 trx250r running stock 34mm keihin that was running a 150 main 48 pilot with air screw at 2 turns out and a R1469N needle on the fourth clip with the airbox lid on and the snorkle system intact. Ran perfect and would idle all day. Well I picked up a pipe, unknown brand, but I believe it was an early version of the FMF fatty with silencer. Pics are in another post if someone would like to take a guess as to what it is. I took the intake tract off and am going to run it with the hole on the front of the air box open as well as no lid.
Tried a 160 main with needle on 3rd clip and it wouldn't idle and ran poorly up till full throttle then it took off. Changed the main to a 155 and turned the air screw out 2 1/4 to 2 1/2 and it idles fine and runs prettly well. I think I may need to drop the needle back to the 4th or 5th clip to clean it up all the way. Anyways, does going up from a 150 to a 155 sound reasonable? I bought a 158 also, but haven't had time to try it out. I guess my question is, does the 155 seem to be the a resonable size, as I don't have new plugs handy to do the chop test.