lawn mower backfiring?

Question

I have a 15 h.p Kohler Command 1 cylinder which started backfiring after I replaced the air filter. It would run fine until under a load then start cutting out and backfiring. Just on a whim, I took the plastic cover off of the air cleaner assembly, leaving the air filter and the foam pre-filter on it, and I finished mowing without any problem. I know on some automotive carburetors, if the wing nut is overtightened, it will distort the air horn and cause a vacuum leak. Could this be a similar problem?

Answer 1

Backfire usualy indicates too lean of air/fuel mixture.

On the botom of the carburetor, open the primary mix needle about 1/4 of a turn.

Also check the two mounting screws holding the carburetor to the side of the engine. (they're a bugger to get to) Make sure they're snug.....not tight....

The only other thing I can think of is the fuel caps breather is plugged causing a vapor lock in the tank.

Try a new spark plug to. Especialy if its a "Champion" spark plug. they suck......

Answer 2

If this has a filter that requires oil on it, check to make sure the foam is not OVER oiled. Too much oil in there will restrict air flow and cause problems. Also replace the spark plug if it looks cruddy or worn.

All the small engines I've ever worked on have a mixture adjustment on the main jet. Try fiddling with the mixture screw.

Answer 3

You can't have a vacuum leak above the throttle plate. I would suspect the air filter. Put the old one back on and see if it works better. As mentioned too much oil on the prefilter will cause it to be blocked somewhat. Or if you got oil on the paper filter it would clog quickly.

Answer 4

You probably need a spark plug.

Answer 5

maybe there is water in the gas.