I have a 1978 kawasaki kl 250. Can,t get it to run right. When i start it and it is at idle it runs alright but soon as i give it throttle it won,t return to idle without adjusting the idle screw out to the point where it stalls.screw it back in and it starts and idles again but does the same thing when i give it throttle.cleaned everything.soaked it in carb cleaner blew out passages and they all seem to be clear. Found the arm on return worn and loose and it was holding throttle valve open. Spot welded that thought that would do it but same problem still. Carb parts other than gaskets looked ok. Got new carb kit but main jet was different. Anyone know about switching it out for brand new. It is a keihin pw 28. Thanks...hobly