Diagnose and Repair a V Twin Running on One Cylinder

Spark, fuel, compression, and valve motion must be tested in order when a V-twin bogs, surges, and loses power under deck load.

Why I did it this way

My zero-turn mower used a 24 hp, 725 cc V-twin engine, specification PS-KT735-3013, serial 4334705844. The final cause was a dislodged left intake pushrod, but the path included compression testing, coil swapping, head work, and valve adjustment.

What I used

• Spark plug socket and hand tools
• Compression tester
• 0.25 mm feeler gauge
• Torque wrench and engine service information
• Correct gaskets, head parts, and sensor-safe RTV

What I did

1. I confirmed the dead side. Removing the left plug lead did not change engine operation. The left plug was wet while the working side was hot.
2. I eliminated ignition as the cause. Spark was strong and swapping coils did not move the failure.
3. I compared compression side to side. The right measured about 180 psi. The left measured 0, later 34 to 36 psi, proving a mechanical problem.
4. I inspected the head, sealing surfaces, and valves. Head and gasket work restored left compression to roughly 180 psi and once near 220, but the cylinder still needed correct intake operation.
5. I watched both valves move. The decisive finding was the left intake pushrod out of position.
6. I reseated the intake pushrod. Confirm both ends remain located through a full hand-rotated valve cycle.
7. I set the lash at top dead center on the compression stroke. Both valves must be closed. Set the recorded clearance to 0.25 mm with light gauge drag.
8. I resealed the cover and tested in stages. Reseal the valve cover with RTV, cure as directed, then test idle, full governed speed, and deck load. The mower ran properly.

What I learned

• Assuming a wet plug proves carburetor failure
• Adjusting the governor to mask a dead cylinder
• Replacing parts before side-to-side tests
• Setting lash at the wrong crank position
• Inventing head torque values

My result

After I reseated the left intake pushrod, set the valve lash to 0.25 mm, and resealed the valve cover, the mower started, ran at full governed speed, and carried the deck load normally.

Know your limits

Stop for a bent pushrod, repeated dislodgement, damaged rocker/lifter/valve, metal in oil, binding engine, or compression that remains far below the other cylinder.

How to adapt this to your project

Use your engine's model-specific service specifications and compare the two cylinders methodically. Compression, ignition and valve motion help narrow the cause; my engine's parts and clearances may not fit yours.