Scotts S1642 hesitates then dies when PTO engaged

I have a Scotts S1642 with Kohler Command 16 (CV16) spec 43526, with the Walbro carb. A condition started 2 months ago that I'm not sure how to diagnose or repair. The mower would start fine, but when I engaged the PTO at full throttle, the engine would hesitate. I could lower the throttle, and the engine would resume, and then I could slowly go back to full throttle and cut the grass. This progressed into when I used the lawn mower after about 30 minutes, the engine would hesitate then die. I have to repeat the whole process again, and finish the lawn. I rebuilt the carb, which didn't seem to help. I took the carb off again to make sure I didn't miss anything, re-cleaned, and reinstalled. Right now, the mower starts fine, runs strong, and will go thru full throttle range as expected, but when I engage the PTO, the only way I can keep the engine running is at lowest throttle setting. If I throttle up any, the engine hesitate and dies, and if I disengage the PTO, the engine goes back to running perfect.

I went from having to engage the PTO at half-throttle, to engine cut-off after 30 minutes of use, to now engine will only stay running with PTO engaged at lowest throttle setting. Anything higher throttle and engine shuts off. Disengage PTO, engine runs fine.

What could cause this condition?

I would check the high speed jet in the carb as well as the operation of the fuel solenoid on the bottom of the carb. Something is restricting the fuel flow under load. Sounds like a partial blockage on the high speed jet.

I replaced the fuel solenoid when I rebuilt the carb, and I hear it click to open before I start the mower. There are two adjustment screws on the Walbro carb, but I've never messed with them, supposedly they are set from the mfg. I just pulled and cleaned the carb for the second time a month ago, and the condition seemed to get worse.

So something is not supplying the engine with enough fuel when there is a load, and this is why the engine is fine at idle, regardless of throttle setting?


I know the screws are for idle adjustments, so based on the above, the adjustments on the screws would have no bearing when the engine is under load (thereby creating a vacuum in the carb?) and not sitting at idle and at atmospheric pressure?

I'm trying to learn the why as well as the how.

The fuel lines are good, the fuel filter replaced during a PM session when I rebuilt the deck in Oct 2014. I've used ethanol free 100% gas for the past few years (as soon as they had a station that carried it in my area).

Just for kicks, I was going to remove the fuel tank gas cap and see what happened in the event the tank cap was not venting properly. I don't know if this would do any good or not.

What is the recommendation on how to proceed?

I have this same problem, except mine is a Scott's 2046 Briggs&Stratton. Will crank fine, and idle fine, then when engaging the blades it starts to act as if I have pulled choke lever up, and will eventually die. I have to lower RPMs, start blades, then slowly increase engine RPMs. If I encounter tough grass or a small hill, engine begins to choke out again.
Please help.
Jim