1990 DR350s hanging idle

Ok folks. I have a few issues with this bike, and it's driving me insane. 

History-1990 DR350s, always been a bear to start. 137.5 main jet, 42.5 pilot. Cleaned the carb more times than I can count. Would love it to start well-but that's not my real problem. I cannot get it to run well consistently. It was really boggy in the low end of first second and third gear. I have tried adjusting my mixture screw multiple times-from 1 to 3 turns. Bike would run great for a few hours, then would start bogging down again. I decided to adjust the valves. Before I did this I was running about 1.5 turns from seated with the mixture screw. After adjusting valves the bike was running very lean-now I'm out to 2.5 turns. The rpm's hang horribly-unless I turn the idle screw out to the point where I'm almost stalling. This doesn't completely solve the problem however. If I accelerate slowly no problems, but if I open up the throttle I get very high rpm's with very little acceleration. Vacuum leak? The petcock is a raptor petcock, and the old vacuum line is capped. the previous owner had cut out the top of the air box (The jets are slightly larger than stock-but not as big as Jesse had recommended for the air box mod) and I've run it with the top removed and in place-same results. Seems I can get it dialed in, but after a few hours of riding, she regresses. I'm throwing myself here. I'm no mechanic, but I am capable of doing the work, apparently just not diagnosing!! going to look for vacuum leak tomorrow, and I have an extended mixture screw on the way so I can adjust the mixture with the bike running (it's impossible to be precise with the stock screw unless the carb is off) anybody have any other ideas??  

contact derek (motolab)


Im sure this is no help but have you made sure the rear right hand side tube to carb is clear? And bottom float line is clear?

I had same issue on my 1991 DR350. Turned out to be gas in the oil, vaporizing and raising idle as it warmed up. Changed the oil and the gas petcock, problem solved. I also drain the carb bowl when I trailer or store for any length of time. Hope it works for you.


Make all your adjustments once the bike has reached operating temp. This could be 15-20 minutes of idle or 5-10 minutes of hard riding.

Rule out any air leaks (even tiny) around the carb boots and exhaust pipe.

Try moving up one clip position on the carb, this helped a lot with my idle.

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