Brigs & Strat TwinCyl V on Craftsman mower. First indication of trouble black smoking exhaust. Sparks Ok on both cylendars, new plugs. Rebuilt carburator first, no luck :mad: Pulled spark plug and used air compressor to pressure cylendar while operating valves....All valves sound like seating. Yet engine coughs and spits gas out front of carb when air filter removed. I thought sticking valves.... so squirted solvent on valve stems, it then ran perfect about an hour, then started black smoke and loosing power again. At this point I am thinking sticking intake valve. I want to avoid rebuilding engine. If sticking is there an oil treatment, possibly dilute oil with 50/50 Keorocene and run for 5 minutes??? Are sticking valves normal in this type of engine? Can valve guides be removed from under valve cover and cleaned? :confused:

if its valves it would be backfiring. you could use kerosene to try if it works but 50/50 shouldn't be used for too long. i would clean the heads and all off by hand and with carb cleaner. your black smoke would be too much fuel from a little offset screw or the springs are needing to be replaced because they aren't strong enough but you can test for that with a tester. make sure the exhaust isn't clogged, the hole thing the oulet and mufflers. most likely the carbs not set right so check them. most like to screw out and they might be bent a little. make sure the jets are clean. if you want to use oil treatment, regular treatment for a car will work not cheapo stuff. stp works for me. don't use much maybe an ounce or two or three depending on amount of oil. i rebuilt a carb before it ran fine then it went to puffing black smoke then it went back right. led me to the screws. they weren't set right.. but try cleaning also the intake as well as the exhaust leading to the valves. try using a can of cleaner while running to try that first. most of the time that will fix the problem. sometimes it won't. good luck.

way too rich of a fuel air mix

tip on diagnosis for a couple probs. black smoke means a gas problem, white is an oil problem from too much to a broken ring or the heads been pointing downwards too much. usually black smoke is from carb problems. 2-cycles you have to tell from how ruff they run. no oil but whats in the gas so you get a combo.