I have a 4yr old INTEK that is slowing loosing power. (Engine Model #33R877/0008-G1)
New camshaft - 10/27/23 which fixed the broken compression relief. Seemed to run great after I put it back together.
After mowing six times this year I have low power and it is getting worse.
 
What I have done so far that has not helped at all:
Tune up 6/01/24 - Air filter, fuel filter, spark plug
Checked flywheel KEY - it was fine
Checked valve adjustment - it was fine
6/7/24 - Replaced carburetor and it runs slightly worse...won't idle all the way down
Always kept good clean oil in it. Because it lugs down more when mowing I removed the deck belt and spun all the spindles and pulleys which were fine. 
Questions:
Could the compression relief be stuck giving me low compression (hard to check and never heard of that happening)
I see some INTEK engines have head gasket problems - I see on sign of that, no oil leaks, smoke, or odd sounds.
I have mowed 1/2 acre of level lawn six times and it seems like I have about half the HP I should have.
Thanks for any ideas or things to check.
Mike
 
 
 
 

RE the carb, is it OEM or aftermarket?   Did the not want to idle START with the new
carb?
 
Generally, not wanting to idle down is a sign of the engine running lean / not enough fuel. 
IE, leaking intake manifold / missing gasket/ o-ring , carb could be lean.   
 
If you partially, by hand, activate the choke, make it run richer, will the idle come down?
 
Ruling out the fueling issues, a "Leak Down test" would tell if there's any "health" issues 
with the engine itself.  IE, air coming out of the carb indicates and intake valve leaking.
 
.
 

Thanks for the quick reply. The high idle DID start with the new aftermarket carb (I may put the old one back on as the new one did NOT restore power). Didn't try 'hand choke' however pushing the governor back a little does cause it to idle down. 
The cam was aftermarket also (hard to find an OEM one). I wounder if the compression release weight is not swinging out to give full compression at higher RPMS. Hate to split the block again to check it.
Any other ideas for low power? I am pretty good with small engines but I am not sure whats going on with this one.
 

I'd get rid f that non OEM carb.  Their a 50 50 chance of them working correctly..
 
Can you go thru the OEM carb, check and clean? 
 
 Does that OEM carb have 2 Philips head screws holding the bowl in (a NIKKI Carb), or 1 bolt right in the middle?
 
The NIKKI Carb has a weird gasket and plastic internals. Try not to disturb the gasket and ESPECIALLY 
the little O-ring. (in the middle).  If that o-ring is gone/damaged, the carb WILL FLOOD the engine. 
 
You'll see a very tiny jet dead smack in the middle/extended plastic part.  That has to be super clean. 
Make sure it's re-inserted correctly or the entire plastic part will not fully seat..
 
Lets get the fuel system back to normal and go from there..
 
The gasket and lil o-ring: 
I put just a smidge of di-electric grease on the lil o-ring to help it slide in when re-assembling..
 

 
 

It wouldn't hurt to re-set the governor as well:

https://www.youtube.com/watch?v=XbFyGRixoGA&t=411s 

Thanks again. NO screws holding the carb,  only the anti-backfire solenoid. I did remove the solenoid and bowl, it was very clean inside. I still think I will put the OEM carb back on. However the carbs did not make any difference in motor power. I may try to determine if the head gasket is falling. That makes some sense to me as the power loss has happened over the last several hours of mowing, it did not happen suddenly. What do you think? Where do you order parts, like a head gasket??

I would test the engines health with a "leak down tester".
That'll show a leak internally.
 
You may be able to borrow one from an automotive  parts store.
 
 

Great idea which should check valves and head gasket without removing the head. I made a crude one 25 years ago out of an old spark plug and pressure gauge...wounder where it is

You can just pressurize the cylinder with a "spark plug thread fitting), with the crank locked up at TDC on the compression stroke.  
 
You won't have a gauge to look at but if you hear air coming from a valve, you now know there's issues there...
 
.

Just ordered a Leak down tester on Amazon. I will have it late next week and will let you know what I find.