Posted by Pete7 on October 13, 2010 at 17:40:40 from (71.243.180.182):
I've got a Farmall 340 that is missing pretty bad at high speed (over 1500 RPM) while under load. Doesn't miss except at high speed while under load. It runs nice at idle and all the way up to full throttle when not under load. I've been looking for this miss for awhile and have replaced the plugs, wires, points, condenser, coil, cap and rotor. The point gap is at.020, plugs at .023 and the timing is on the mark. Gone thru the fuel system also. Soaked and blew out the carb, set the float level and checked for good fuel flow. No plugged elbow screen either. All seems good on the fuel/carb system. I have set the valves at .014 while warm. Engine reads 125 lb of compression in each cylinder and a vacuum gauge reads steady at 20 inches while at idle. While at high speed and under load the vacuum gauge bounces downward about 4-6 inches (to 14-16 inches). So, I'm thinking I might have a valve problem? Or another possibility might be a worn bushing on the distributor shaft. I can feel some radial play in the shaft, but I'm not sure how to better tell if this is the cause of the miss. Both a valve problem and a wobbly rotor seem likely at high speed to cause a miss, but why only under load. Or maybe I'm on the wrong track? Any ideas? Pete
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