So I had a 2004 klx 125 that I traded for this 1998 scrambler 400. I was told the carb needed adjusted it wouldn’t idle low and gas comes out overflow. I figured clean the carb and adjust to stock specs. Also was told he disconnected the oil pump and started to premix due to what he read online. So I traded. Then I found there was no air box. I figured definitely clean carb and but intake box. Took carb apart and fount it clean looks like it was rebuild. Check the specs for jets and all are correct. Put back together put airbox on and it wouldn’t start. Took the airbox off and it started up. Even with only air filter off same problem had to take the whole thing off. Now I put the air box on with it running and it bogged down hit the throttle and it spun up but very little power. Any suggestions.