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I have a kt735 spec 0005g1 that is surging bad. I've set the valve clearance, new plugs, new oem (walbro) carb. I checked compression and one cylinder has 125 lbs and the other has 97 lbs of compression. does this indicate a blown head gasget? can there be any other issues?

Does it surge under load when cutting Grass or just running at idle

Tank vent clogged.

Bugs, grass, dirt dobbers and grit in the fuel tank. Rubber pieces from tank cap deterioration in tank. All this trash will limit slash block flow from tank.

Fuel lines deteriorate from the inside. Replace all lines to carb.

Fuel filters plug up.

Using an old style gas can with the open top. Get a new style can to keep fuel fresher and less contaminated.

Gov-na' spring/linkage might be messed up, stretched or who knows?? Governor might be incorrectly set up.

Your second question about psi numbers. Indicates either valve issues or poor rings on one cylinder. Do a leak-down test.

According to the service manual for your engine compression should be a minimum of 160 psi with no more than a 15% difference between cylinders. So you have bigger issues than just a surge.

Can you inspect the area around the suspected blown head gasket?
A cylinder leak down test might be helpful.
Keep us posted!
Doug Lee
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smallenginerepairs said:

I have a kt735 spec 0005g1 that is surging bad. I've set the valve clearance, new plugs, new oem (walbro) carb. I checked compression and one cylinder has 125 lbs and the other has 97 lbs of compression. does this indicate a blown head gasget? can there be any other issues?

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Have you verified both cylinders are actually firing?

Spray a shot of water on each exhaust pipe and watch for it to boil off immediately. The one not boiling off is the none firing cylinder.

These V-twin engines will fool a person because there is no imbalance/ vibration. Pull the upper fan shroud and disconnect the single wire on each coil. Then fire it up and check for more power and no surge.
This usually means the "kill" harness to the coils is bad. The inline mini diodes typically fail.

Often times, people replace a coil and never check this harness.

If it has been jump started multiple times in the past, it will often blow these diodes out.

Auto Doc's said:

Often times, people replace a coil and never check this harness.

If it has been jump started multiple times in the past, it will often blow these diodes out.

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Right right..........

slomo said:

Right right..........

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if the diode was blown the coil would not fire. I have put spark testers on both coils and both coils are firing. I also took the kill wires off both coils which would eliminate all wiring and still no fire on the one cylinder.

smallenginerepairs said:

if the diode was blown the coil would not fire. I have put spark testers on both coils and both coils are firing. I also took the kill wires off both coils which would eliminate all wiring and still no fire on the one cylinder.

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also I have cleaned the fins on the heads now they were clogged enough to blow the head gasket on that cylinder, but I replaced the headmaster and that cylinder still will not fire.

smallenginerepairs said:

headmaster

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headmaster not master.

smallenginerepairs said:

headmaster not master.

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head gasket not headmaster. my spell checker is at it again.

smallenginerepairs said:

also I have cleaned the fins on the heads now they were clogged enough to blow the head gasket on that cylinder, but I replaced the headmaster and that cylinder still will not fire.

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What are you calling a headmaster? Is that the cylinder head? A regional term I have never heard of?

Did you resurface the head with fine sandpaper on a good flat surface like a glass tabletop before installing it? Was the gasket replaced and the head bolts torqued properly?

In each cylinder you have to have ignition spark, fuel and compression in the right combination to run. Which is missing?

Have you measured the compression on each cylinder (again)? If it is still very low in the non-firing cylinder, then it could be heat damaged, collapsed piston rings

Are the valves properly adjusted (again) (There are many videos online about how to do this).

Was the head a used one and not checked before installing?

Has the carburetor been opened up and thoroughly cleaned? (New does not always mean good) Is there a leak where the intake bolts down to the head?

Last but not least, are the spark plugs correct for this application? I use Champion most of the time.

Auto Doc's said:

I use Champion most of the time.

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Use what works for you but I prefer NGK. Not for nothing.