I have a 3 cylinder, 60 hp, Merc Model 60, circa 1985. Last year the motor would start right up, but only run on two cylinders. After 10 or 15 minutes of running time the third cylinder would kick in and the motor would run fine the rest of the day. I've changed spark plugs, and done some preliminary tests on the wires and the coils. The shop manual does not list this problem in its troubleshooting section. Any ideas?

Have a 1986 Mercruiser 170 (4cyl), I/O Alpha 1, closed cooling system (antifreeze) for 5 yrs. Previous owner (original) warned us that he had an engine run problem sometimes after a hard run. When outside temp gets hot 90+ degrees and engine runs for maybe 1/2 hr the engine will stall at low speed. Starts right up and acceleration OK in neutral, but stalls in gear. Can play with the accelerator (pump it lightly) while in gear and get it going and runs OK at high speed. Waiting about 1 hr until things cool down returns the operation to normal. This has been going on now for 5 yrs. We have been through 3 tuneups (plugs, points,cap rotor, cap), wires, coil, filters, batteries, 1 voltage regulator, clean gas tank, carborator cleaner, out unit servicing, sea water pump. Engine temp is normal at 160 degrees. We are suspecting a vapor lock problem since we don't seem to have the problem in cooler weather. Any suggestions on a test method and fix?? Our mercruiser service book talks about a vapor lock problem on 4 cyl engines; Mercruiser fix with a high volume fuel pump kit (#42725A5) and water cooled fuel line. They claim Mercruiser made this a standard item on engines made after Aug 1986. Ours was made in late 1985. I've tried 2 Mercruiser mechanics and they have never heard of a vapor lock kit or water cooled fuel line. Does anyone have any experience with this? Tom