Dogbane cooked my 8199G

[RichardTX]

I have a friend that has a 18G and he has adjusted his so that the engine spins at 3600 RPM. He swears by the added RPM and power. When I had a M18 I ran it at 3600 RPM. The added RPM does help.

I have since upgraded my G series tractor and replaced the Kohler Magnum 18 with a 24hp Onan. That turned out so well that I replaced all of the Kohler engines on my 4 wheel tractors with Onan engines.

Popping thru the exhaust on shutdown in almost normal on those Kohler twin engines. To help stop that from occurring, let the tractor idle for a minute and then shut it down. It may not stop it but it should be less frequent.

 

[daugen]

initial diagnosis was water in the gas. Never had that as an issue before on this Gravely. I had the dealer drain and flush the gas, we shall see.
and I put a new set of NGK UR4 plat plugs in, something nice for the holidays...
Will pick up on Monday.

 

[daugen]

Popping thru the exhaust on shutdown in almost normal on those Kohler twin engines. To help stop that from occurring, let the tractor idle for a minute and then shut it down. It may not stop it but it should be less frequent.

an update. Now little popping when shutting down, but a huge bang when I start the warm engine without using the choke. Am I running too lean? Otherwise it runs fine.

 

[RichardTX]

Sounds normal to me. Best way to prevent it is to let it idle for a minute or three after running it hard.

 

[daugen]

Richard,
normal can't be letting off a bang that can be heard a mile away.
And almost every time I start it when warm. When cold, using the choke, no problem.
I'm going to do the obvious things like check the plugs (nice plat NGK...) due to the
electronic ignition conversion kit I put on, make sure nothing looks strange there, but if the plugs
are clean, which frankly I'd expect if it were running lean, then what else could it be other than a carb
adjust?

I understand the popping when stopping. It's the bang when starting, and I'm talking a seriously loud bang, not some little pop, that concerns me. Have to wonder what all that is doing to the valves, etc.
Since I can eliminate it by pulling out the choke some, I still think I should do a carb adjust. Can't hurt....

 

[RichardTX]

If you really want to solve the problem, shut off the fuel at the tank and let it idle until it runs out of fuel. It is a little extreme but it works.

What happens is that when you shut the ignition, the engine continues to spin sucking fuel out of the carb, throught the cylinder and out the exhaust. air creeps in from the tail pipe, hits the hot fuel mix in the muffler and BANG! There are other scenarios that also result in a muffler explosion. Have you ever noticed the lack of a bang if you stall out the engine?

You could try putting a longer tailpipe on it. That will permit the fuel in the muffler to cool below the flash point before air gets in. I have had delayed bangs. Shut off the tractor, get about 10 ft away and then it goes BANG!

A leak in the exhaust system can also cause a backfire. Let air in at the header where it bolts to the engine and that can cause a big bang at shudown. You might try replacing the exhaust manifold gaskets. When I remove exhaust bolts, I replace them with stainless SHCS. A little high temp Sevr-Seez helps keep the threads from galling.