What do these pictures indicate? (top-end)

[TxState]

I've been having intermittent power issues and low top speed that wasn't solved by a carburetor rebuild.
Compression was reading at 135psi and 140psi. Pulled the coolant block and the top off the cyclinders and this is what I found.
What does this indicate about how the motor is running? What should I look at specifically as the source for my compression loss?
Any insight is appreciated.

 

[racerxxx]

Looks like the PTO piston has been replaced in the past. Have you verified the entire carb? Like all the passages flow? I take a squirt can for oil and fill it with automatic trans fluid (red in color) and I squirt it in every port to verify all passages "flow". If you google Mikuni SBN you'll find a cutaway diagram from Mikuni I think that will show the flow.

 

[TxState]

I'm actually going to rebuild the carburetor again with a genuine mikuni kit this time. I'll do flow checks like you suggested. How do you clean the trans fluid out when you're done? I'm worried that shooting carb cleaner in there would dissolve some of the plastic or rubber components.

What could be causing this oil gunk buildup on the pistons though? I'm assuming they are not supposed to look like that.

 

[jts32]

Some carbon build up on the pistons is normal and means your running at a correct fuel mix. The mag piston looks a pretty normal, maybe running a little lean. The PTO piston looks like it was probably replaced. What did the plugs look like on each? Rebuild the carbs with mikuni parts. Tear them completely apart and spray every passage with cleaner and compressed air. Do a pop off test and pressure check the rest of the fuel system. Also check and clean the raves, large power loss if they aren't preforming correctly

 

[fester]

One side is richer than the other front should be a little leaner than rear

 

[fester]

Check fuel lines from sending unit esp if the tiny filter in carbs are black and gunked up the fuel lines are known to deteriorate.

 

[fester]

Compression should be 150 in both but what you have is sufficient.

 

[Chester]

MAG piston is a good pattern, not rich or lean. PTO piston is very lean.

Chester

 

[fester]

Looks like possible water intrusion on mag side also!