Had a family emergency and had to step away from my M43 problem. Am now back at it and family issue came out fine.
I tested the compression 1= 100, 2 =95, 3=97, 4=95, 5=98, 6=100.
I think compression is not a problem.
I pulled number one plug to check for spark. Grounded the plug body to the engine and cranked it over. I got a yellow spark (not a sharp blue spark) that seemed weak to me? Could the coil, points or condenser be the problem and fail after warming up? I have bought new replacement coil, points and condenser and think I will be changing them out.
The problem I have had from the start is a follows.
Starts up O.K.
Left to idle and warm up the engine will eventually slow up and die after warming up. It then will not restart unless you let it sit for quite a while.
The plugs all show black soot as though the fuel is not being completely burned. Replaced all plugs new. Rebuilt carburetor, checked for correct timing (it is within a degree or two).
Checked compression and all are within range.
Checked idle adjustment setting and fuel mixture setting. Gauged the carburetor float to spec when rebuilding carb. Idle screw was set at 3/4 turn from closed
Vacuum is around 17 - 18 (air filter and carburetor horn removed. Air lines to distributor from carburetor horn are disconnected)
Throttle advance or revving after initial start up responds as it should until the engine warms up and dies.
Does anyone have any ideas as to what could be causing this?