My lawntractor just today all of a sudden dropped rpm and ran rough with little power and with blue smoke out the exhaust. Smells like gasoline. I looked at the carb. and the valves looked right. Choke seems to work. Cleaned plugs. Took air cleaner off and rpm goes up but still with little power. Some kind of fuel problem. 5 year old tractor, 18.5hp twin cyl. I know this is car talk not lawn talk.


Have you verified you are getting a spark to both cylinders? It sounds like it might be running on just one.


Yes, I could see (and feel) the spark on both wires. That’s 1 of the 1st things I suspected.


Next thing I would do is a compression test of both cylinders.


I’ll have to get a comp. guage. I can’t see how it would go in the blink of an eye.


I don’t know about the smoke but sure sounds like a carb issue. If its a B&S twin cyl., the fuel pump for those is a fiber diaphram type part that wears. They are only a couple dollars. I’d just put that in and while you’re at it check the float to make sure its not stuck. Or you could be having a spark problem. You could squirt some gas in each cyl. to see if it momentarily revs up to rule out the coil and other serious problems.


Get a compression gauge check each cylinder. Be sure to remove both spark plugs and crank the engine when it’s cold. If compression does not match between cylinders, put a couple squirts of motor oil into the low cylinder and wait a few minutes. Recheck the compression on this cylinder. If the number improves, it’s the rings or a cooked piston. If it remains the same, suspect the valves. However I’m betting on the rings or the piston.

Want to sell it cheap?