M-18 running rough/missing

[john hall]

OK, new thread on the 1811. We've never used this machine other than driving around a bit. The guy I bought it from didn't either. He did have someone try to work on the carb because it wasn't running well. So here is the problem, there appears to be an occasional miss causing it to run rough. Here is what we have done:
compression--right side 130, left 120
spark plugs--runs the same with old or new plugs. Actually pulled the new plugs to put in the old ones. With only 10 minutes of running the new plugs appeared sooty.
carb--cleaned it out (didn't remove welch pugs), opened it up again and bent float tab a bit. Fixed jet Walbro.
intake--I sprayed 2 different types of carb cleaner around where the intake bolts up--no noticeable changes in running
Suspecting a lazy valve--sprayed 2 types of carb cleaner and penetrating oil in the air intake trying to lube things up. Even dumped straight SeaFoam in there also added some to the gas. Not really improving anything. Considering getting some Marvel Mystery oil and putting in the gas like you do when the old cast iron Kohlers have a sticking valve.

Here is the really weird part. If you pull the left plug wire while it is running, it runs worse, but keeps going. If you pull the right wire, it will die within a few seconds--and will backfire when you hook it back up. Even thought the right side is apparently doing more "work", that plug will be colder. After 3-4 minutes I pulled the pugs out and could hold the one on the right. The left "weaker" side was too hot to hold.

I'm thinking lazy valve or bad valve clearance on the left side. Anyone else got a guess?

[cubby102]

Pull the heads and inspect...

[Mike McKown]

Sounds to me like too much gas is getting in the engine.

[yeeter]

maybe throw an induction timing light onto the spark wire and see if consistent signal?

[J-Mech]

Pull the motor. Pull the tins. Pull the head. Something inside isn't right. I'd toss the carb and throw a #26 adjustable from a K series on it. (Don't really toss it, your going to need parts off it to make the #26 work.)

[john hall]

Going to do a quick spark check before I open things up. I saw a gasket kit on ebay for about $40--it included the seals. What's the opinion on el-cheapo gasket sets? I'm sure Kohler gets way more than that for head and valve cover gaskets.

[J-Mech]

I'd get an ebay kit without a second thought. Even if the head gaskets weren't any good, it's not that much money to get a second set.

I buy from this guy:
http://stores.ebay.com/The-Mans-One-...=p4634.c0.m322

I don't see a Mag 18 kit listed, but I'm sure he can get it. May even stock it, but just doesn't have it listed. I always just call him.

[2009Dodge]

Sounds like weak spark. I'd ohm out the wires maybe switch out the coil with a different one before you pull the motor. If it checks out then pull the motor.

[john hall]

OK, I'm pretty sure the coil is crapping out. I took the spark tester off our Allen test machine for magnetos and checked each wire. The wire going to what showed to be the weaker cylinder yesterday barely would create a spark. The other side was about 4-5 times stronger. Tried switching the wires by using an extra wire to see if the "short wire" (right side) would mimick causing the engine to die when it was pulled. Well today it didn't, even when hooked up properly. Even though the short wire was much stronger, the spark was still rather "weak" looking. It failed around 6mm (just under 1/4"), that's the threshold minimum for a magneto before you tear into one of them. I've had several late model magnetos go 11mm (aprox 7/16) before failing. So, prices on coils start at $50 and got to $200. Saw a genuine Kohler for $100. What do you guys recommend, no-name or genuine?

Attached a pic of the spark tester, it will do up to 12 cylinders--checks from
1mm up to around 15. I have NO idea why its metric given its age.

[Mike in SD]

This is where I bought my Genuine Kohler mag coil when I needed one. I have had very good luck with Pats Small Engine.
http://www.psep.biz/store/kohler_52_...ition_coil.htm

HTH,
Mike