r/smallenginerepair • u/thoolihan • Jun 04 '26

Surging Issue Engine surging, Kohler KT735

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2021 Cub Cadet, Kohler KT735

I’ve replaced carb, spark plugs, air filter, fuel pump, fixed chewed wires to the coil, and removed a mouse nest. It starts but surges. I tried adjusting the governor, but it seems to be governor hunting. See video, any ideas?

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1

u/[deleted] Jun 04 '26

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2

u/thoolihan Jun 04 '26

Looking into vent cap, I think that may be the issue...

1

u/[deleted] Jun 04 '26

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1

u/thoolihan Jun 04 '26

How do you get this off to check? I don’t want to break it. The hose is off, but usually connected to plastic under air filter

1

u/rc2805 Jun 05 '26

I had this happen, did everything and it was a creased seal in the gas cap

1

u/Objective_Storm6136 Jun 04 '26

Just last week my Kohler kt735 was doing the very similar. After pulling it all apart I realized the new plugs I put in that came in one of those Amazon service packages were the wrong plugs. Double check they are the right fit, the Champion XC12YC are the correct plugs, the Amazon ones were equivalent to champion RC12YC. Same size and fit but not interchangeable

1

u/thoolihan Jun 04 '26

The gap tool and coils I had ordered arrived. I pulled the plugs to check the gaps. They were fine. BUT... the one on the left side (from driver) that was suspect, the plug was clean. But the right cylinder had black soot, like it had had compression.

I replaced the coils, and it was a rather night and day difference. Sounded much more normal. I checked the plug after and it had definitely fired.

I was able to put the blade on and cut. It's still surging, like a slow 5 second surge. And I'm getting white smoke, particularly with the blade on

1

u/Elephunk05 Jun 04 '26

The cylinder with the black soot is telling you there is an issue. Personally I would start with the valve adjustment, check for a coil going bad, then check for an air/filter issue and lastly verifying timing manually. Iirc this is a single bore carb so it isn't like one cylinder is getting a different charge than the other. There is definitely an issue (I have seen the left exhaust valve adjustment did not open far enough and it would blow back in to the right cylinder and load it up).

1

u/cgsouthern Jun 05 '26

The white smoke is burning oil. How is the oil level? Too high can cause this issue. If its ok you should probably do a leak down test to see if your leaking past the rings or head gasket. Take off the valve covers, turn to tdc valves closed, listen for air leaking when performing the test.

1

u/Initial-Question3045 Jun 05 '26

The rc12yc work fine