PTO strains as it spins up blades. Then weakly declines as soon as it starts cutting.

[ILENGINE]

Spark plug, coil, valve clearances, and even head gasket can all be possible causes.

 

[kabacrew]

Here is he rub that most people seem to miss.
You test things to verify if they are working or not rather than making blind stabs in the dark.
There is an engine in the workshop with a complete piston & rod missing.
The customer had the mower for 5 years and thought it was a bit gutless.
It had been serviced 3 time by the vendor.
He was ill & his wife could not start it so she called my predecsor.
There was not a mark on the crankshaft, the engine left the factory with only one piston.
Briggs did the right thing & sent a replacement engine.
So the first thing to do is pull one plug out, ground the plug and try to start the engine.
Do it for both sides
Each side should start & run the same if both cylinders are working.
IF one side is not working then we do some more digging around to find out why it is not working.

Thank you. That's one heck of a situation there and it makes a good point.

I checked the cylinders by removing the plug caps one and then the other. They both fired up equally.
I think / guess I should drop the belt and check each spindle bearing for play or misalignment next. I'm open to any other suggestions too of course.
If those are fine and I get to the clutch, are there any hand turning type of checks or such that can be done there?

 

[kabacrew]

I have dropped belt and checked spindles. They spin freely.
The PTO clutch... I can turn it with a little force when not engaged. None when it is engaged. I think that is as it should be. When I engage it with the belt dropped it barely blinks.

I am thinking next of cleaning carburetor and maybe replacing the fuel pump.

Any comments or redirection will be appreciated. Thanks in advance.