So they're CV carbs or not? You mention a diaphragm.Agreed. The Makuni has a slide, not a butterfly and they're prone to leaks on older ones, as the diaphram goes bad. Causes a lean running condition, but Taweste says it's NOT the carb.
I had this EXACT same problem. I found the thread here looking for a solution to it. The solution for me, after I'd tried everything else, was checking and setting the exhaust valve clearance. Problem solved. Check your valve clearances.Alright, so after some messing around, I've realized that if i lower the idle adjustment screw down to a point where the engine does not idle, the problem stops. But, the new problem is the fact that I have no idle.
I tried to adjust to the point where I get a functional idle, but as soon as the idle is there, the problem with the engine ceasing to come back down begins again. I cannot reach a happy medium, with the idle adjustment screw.
Would the idle air/fuel mixture be causing any of this?