I have a strange engine problem. At idle, the engine runs very well. No coughing, no spitting, no backfiring. My CB Performance A/F monitor says it is idling between 14 and 15, which is almost perfect. When I roll on the throttle, it leans out slightly, then picks up. Again, no backfiring, popping or spitting.
But, when it sits at a constant speed, between 2500 and 3500 rpm, the needle drops to nothing. It goes extremely lean. I can let off the throttle or roll on and it jumps back to slightly rich. If I hold it steady, it goes very lean again.
I've cleaned both carbs thoroughly (44 Webers), adjusted the floats, replaced all the gaskets and checked for air leaks but can't find any. The only oddity is that the #1 cylinder isn't flowing as much air as the other three according to my snail guage. That was until today when I suddenly found a small film of oil by the #2 sparkplug, and I had a few drops under the car.
Could the cylinder head be loose, and could that be causing the lean condition at constant rpm? I'm going to adjust the valves again and will check the cylinder head torque then, but would appreciate any thoughts as to if that could be the cause of the motor going so lean and would appreciate any other ideas.
It is a 2187cc Scat "0" Mile motor. The stock oil temp guage indicates the temp is staying low, and the cylinder head temp guage is at 350 max, but usually runs 325 or just slightly higher. However, the engine only has about 50 miles on it.
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