1. New plugs, electronic ignition, rebuilt YH Carter carbs;
2. Easy start, smooth idle;
3. Misses and sputters for about 10 minutes and then smooths out:
4. At shut off:
b. Plugs in cylinder #5 and #6 fouled (black soot). (I believe cylinders 5 & 6 are fed by rear carburetor)
5. If I keep motor running, engine runs smoothly.
Is it possible there is a blockage in the rear carburetor? Any other ideas?