hi , i have a craftsman riding mower with a twin cylinder 18 hp kohler . its running rough , runs a little better when choke knob is pulled about half way, it has new spark plugs , new airfilter with precleaner ,new ignition switch,new power relay and new pto switch, i tested the spark on each cylinder and they do have spark, when i pull the left side (facing the engine) spark plug wire engine will cut off. when the right side plug wire is pulled engine will not cut off. can anybody tell me if its the ignition coil? carb? or other?
thanks in advance
jesse

Probably other...

If you have spark, but the engine is only running on one cylinder, then there may be a problem with the valves, I don't think the carburetor on this engine will cause this.

I'm also guessing the valves.When we had those on Grasshopper riders years ago,there was a 500 hour interval for pulling the heads and decarboning.Usually needed a valve job and heads lapped flat by that time.The exhaust valves cooked easily,and if yours is running lean to where you need to pull the choke out partl,it's a good bet.
Doing a leakdown test is best,or a compression test at least will tell for sure.
It's a job to do,since there are so many shrouds,and interlocking pieces that usually means removing from the unit to do.
Back then,the stock exhaust valves were 45 degree,but the replacement valves were 30 degree,so the seats had to be replaced as well,requiring a special puller and installer setup.Maybe now that has changed?

Take care,
Steve

i checked compression on both cylinder and both cylinder has good compression. i also cleaned carb ,, ran mower and runs better but it still has a popping sound out of the exhaust once in a while .. ***note*** the fuse was blown and had to install a new one to get mower started.