Kohler CV740 running rough under load.

[rwhelipilot]

I have a Hustler 927806 with a Kohler CV740 engine.
I bought this mower used and have been restoring it and now that I have it running, there is a problem with it running rough under load.
It runs fine with full throttle and no load, but if I put some load on it such as blades engaged and going uphill, it starts running really rough.
My first thought was that it was starving for fuel. I had already replaced all the fuel lines, tank strainers, selector valve, and filter during renovation, so I then replaced the fuel pump.
The problem persists, so I had a new carburetor on the shelf and installed it.
The problem persists, so I went to the ignition coils. Someone had already replaced the DSAM system with the 25-707-03-S MDI kit, but I replaced the coils AGAIN.
The problem still persists, so I am now leaning toward a valve issue. Perhaps a valve is sticking, not seating, or a hydraulic lifter is bad.
That is the only thing I can think of that could be the issue, now that I have replaced about everything else.

Any thoughts???

 

[Bertrrr]

If it runs good with no load it's doubtful you have a fuel or carburator problem, You need to look at the linkage to the governor first , maybe a spring is missing or the linkage is off , when a load is put on the machine the governor should react and maintain the rpms. Make sure you have good spark plugs etc.

 

[MParr]

I would be checking to see if you are down one cylinder.

 

[rwhelipilot]

If it runs good with no load it's doubtful you have a fuel or carburetor problem, You need to look at the linkage to the governor first , maybe a spring is missing or the linkage is off , when a load is put on the machine the governor should react and maintain the rpms. Make sure you have good spark plugs etc.

Governor linkage looks good, including spring. I really don't think it is the governor because it isn't simply bogging down, but starts running rough as if one cylinder is dropping out. If I stop moving, within a minute, the engine will smooth out again.
I just pulled the heads off today and #1 has a lot of black carbon buildup. Later today, I am going to remove the valves to verify that the seats look good or if they need lapping. While it is apart, I will replace the hydraulic lifters, head gaskets, intake gaskets, and exhaust gaskets. I read in the forum where someone said the lifters can cause this sort of thing and someone replace them and the problem cleared up.

 

[MParr]

Governor linkage looks good, including spring. I really don't think it is the governor because it isn't simply bogging down, but starts running rough as if one cylinder is dropping out. If I stop moving, within a minute, the engine will smooth out again.
I just pulled the heads off today and #1 has a lot of black carbon buildup. Later today, I am going to remove the valves to verify that the seats look good or if they need lapping. While it is apart, I will replace the hydraulic lifters, head gaskets, intake gaskets, and exhaust gaskets. I read in the forum where someone said the lifters can cause this sort of thing and someone replace them and the problem cleared up.

Coils can also be a cause.

 

[slomo]

Carb float level could be set low. Restriction in fuel delivery to carb.

 

[rwhelipilot]

Coils can also be a cause.

Already replace those. Same issue.

 

[rwhelipilot]

Carb float level could be set low. Restriction in fuel delivery to carb.

I don't know the history of the mower as I just bought it and have been restoring it. Cooling fins are not too dirty, but while I have the heads off, will clean it thoroughly.

 

[Bertrrr]

Sounds like you're pretty handy with this type of work, Let us know what it ends up being

 

[rwhelipilot]

Sounds like you're pretty handy with this type of work, Let us know what it ends up being

Yes, the next step is to order some parts. I hope this solves the issue. I'll keep you posted.
One thing I thought of after the fact...I should have did a compression test before pulling the heads off. If it ends up needing rings, I will be pulling the heads back off.