# Gt5000 craftsman w/ 26hp Kohler



## Jeff Joyce (7 mo ago)

I'm having an issue with the engine backfiring when you try to accelerate. It's almost like a prededination knock. When you pull the plug wire off the plug with the engine running, the knock goes away, and while it's still weak, it's not knocking. I replaced the module for that side and doing the same thing. I pulled the front cover on the affected side and checked the pushrods and rockers, and they don't seem damaged. I'm on a very fixed income and my back is against the wall. Any ideas that someone can help me with?


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## BigT (Sep 15, 2014)

Howdy Jeff, welcome to the tractor forum.

Here's an interesting video by NGK regarding pre-ignition. It could be caused by a glowing hot spark plug or by a glowing carbon deposit in the combustion chamber. I would first try changing the plugs to meet Kohler's plug specifications. If you cannot get rid of the knock, you may have to pull the head and clean up the carbon deposits in the combustion chamber.


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## BigT (Sep 15, 2014)

Jeff, with your engine backfiring thru the carburetor, keep an eye on the air filter connection. "Spitting up" like that can unseat the air cleaner and result in "dusting" the engine.


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## Jeff Joyce (7 mo ago)

BigT said:


> Howdy Jeff, welcome to the tractor forum.
> 
> Here's an interesting video by NGK regarding pre-ignition. It could be caused by a glowing hot spark plug or by a glowing carbon deposit in the combustion chamber. I would first try changing the plugs to meet Kohler's plug specifications. If you cannot get rid of the knock, you may have to pull the head and clean up the carbon deposits in the combustion chamber.


Thanks Big T. I'm going to watch this in a little while. It makes sense to, cause I just went through carb trouble, and all that comes with that, last year. I have already tried plugs, but was doing the same thing. That's why I pulled the front cover off the side that's having problems.


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## Bob Driver (Nov 1, 2017)

Jeff Joyce said:


> I'm having an issue with the engine backfiring when you try to accelerate. It's almost like a prededination knock. When you pull the plug wire off the plug with the engine running, the knock goes away, and while it's still weak, it's not knocking. I replaced the module for that side and doing the same thing. I pulled the front cover on the affected side and checked the pushrods and rockers, and they don't seem damaged. I'm on a very fixed income and my back is against the wall. Any ideas that someone can help me with?


If it's backfiring through the carburetor on a V-twin, that's usually an intake valve not fully seating. If its a CV Kohler, there's no valve adjustment, they have hydraulic lifters, but they do have "insert" valves seats that can come loose.

A leak down test would tell you if you have a bad valve seat. Here's a Kohler video that shows how to do a Leak down test.
Leak Down Test

They are using a fairly expensive Kohler Leak Down Tester in this video. You can buy them on Amazon for $30 and Auto Zone usually has them in the loaner tool program. If you can't afford an actual tester..... Rotate the suspect cylinder to TDC and rig the crank to stay in place (valves close). Blow 20-30PSI constant shop air pressure into the cylinder through the spark plug hole. Listen carefully with a piece of fuel hose to your ear like a stethoscope.....
*
Air coming out the exhaust* --- Exhaust Valve Leak

*Air coming out the carb* --- Intake Valve Leak

*Air coming out Dipstick Tube* --- Bad Ring(s)


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## Busted Tractor (May 22, 2018)

While you had the valve cover off did you turn the engine over and watch the valves operate? Have you taken the spark plugs out and using a piece of wire check if the pistons move when you turn the engine over?


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