1999 Craftsman GT3000 - Weak Cylinder?

[pctdavis]

Hello,

Last year I bought a used Craftsman GT3000 garden tractor cira 1999 from what I can tell. This has a 25HP Kohler Engine in it. Lets just say, I knew it would take some work which is why I got it for the price I did. No problem. So far, I have replaced the flywheel (funny how the battery always died on the old owner) and replaced the head gaskets (stopped the smoking). Finally, the tractor is running pretty well. However, there is a lingering issue that I just cant solve.

While running, when I engage the mower deck, the engine really bogs down. It goes from running well under no load to really struggling (especially if going up hill). I tried the test where I pull off only the right spark plug (keeps running) and then pull off only the left spark plug (shuts off). The right spark plug does not show the carbon from 'ignition' that the left does but when I put a spark tester on, it gets plenty of spark. Everything looks and feels right, but it just seems that the right cylinder is weak and I cannot find the root cause. This I think would cause my "weak engine" issue when I put it under load.

Any ideas or thoughts? Thank you.

 

[woodlandfarms]

Compression, Ignition, Fuel. A valve not fully closing, weak spark, fuel starvation to that cylinder.

 

[Zork]

Compression, Ignition, Fuel. A valve not fully closing, weak spark, fuel starvation to that cylinder.

(Good advice)
Valve is not fully opening (adjustment or wear). A dry and wet compression test will let you know for sure if it is upper or lower end problems.

 

[pctdavis]

Thanks. I'll pull the valve covers off and see in anything is wrong. I have it so close.....new stator. New head gaskets. Soon, I'll have it running like it should.

 

[torqotrac]

Thanks. I'll pull the valve covers off and see in anything is wrong. I have it so close.....new stator. New head gaskets. Soon, I'll have it running like it should.

When you have the cover off look "thru" the coils of the valve springs (esp exh) at the position of the valve guide. My BS Intek 24 got weak one day and finally rt cyl stopped, Both cyls had same compression. The rt exh guide had pushed up and loaded up the valve train resulting in a "perfect circle" exhaust cam lobe-no lift. The lifter was perfect. Not uncommon in BS. Ground off exh cam. My take over heat. The exh valve was only opening enough for a compression reading, but not enough for a firing charge.

 

[pctdavis]

Okay, small update. I had some time this weekend to test the compression. This is a Kohler 25HP engine and both cylinders matched perfectly (150psi) and held. I noticed on the carb however that the 'bolt'on the bottom was lose and gas was leaking out. But, it was like it should be like that because the wire wasn't twisted. I tightened it down and my shotgun sounding backfire on shutdown its gone. I don't know why that bolt would have been lose. Any ideas?

 

[pctdavis]

Okay, after much head scratching, I have finally solved the issue. When I did my spark test, it showed to be working fine. What I didn't realize was, the test was wrong. I found a note in the Kohler service manual about ohm measurements on the ignition coil. Turns out it was bad. I feel like an idiot for not checking that sooner, but wow, what a different tractor I have now!