FR691v CS05 sputters as it get's hot.

[Shadrocks]

Losing my mind on this one.. Engine is an FR691V-CS05 on a roughly 10 year old Cub Cadet RTZ 50.
Behavior: Starts and runs good, when cutting under full power the engine starts missing a little then goes down on power.. Stop moving and the engine comes back. Seems to get worse as the engine gets hotter until it will happen even with the PTO off..

What I've done:

• All new carb, fuel filter, fuel lines back to the fuel filter, coil packs, spark plugs, air filter, oil & filter, fuel pump..
• Cleaned fins on cylinder heads, they were packed pretty good.
• Replaced hydraulic belt and deck belt. (This is a separate issue with a weak left side drive. Belt helped tremendously).
• Checked compression yesterday and it was 95 on cyl 1, around 110 on cyl 2. No leak down happening. Minimum spec is 64 in the Kawi spec sheet.
• I've blown air back to the tank to clear the fuel lines.

I am trying to figure out how to get to the lines going to the tank but have to take off the faring's and don't know how to yet.. screws under the tank and on seat mount is what I've seen.
The problem has changed over time. When I started with issues the engine was surging and down on power.
Another question I have is that the vent line from the tank is cracked and dry and needs replacing but where does that line connect? There's a nipple on the carburetor above the fuel inlet, I put on a line to that and plugged it for now... Is that vent line supposed to connect there?
I also need to check for intake leaks using the carb cleaner trick.. Spark plugs are very sooty, but the carb has no fuel adjustment, only an idle screw.

 

[Shadrocks]

Update: Tried the intake leak test by spraying carb cleaner at the cylinder inlets.. No results, no change.
Figured out that removing the tank was not crazy hard, some fender screws and loosen the fender. There's a frame mounted plate that holds the tank in. Nothing crazy in the tank except there was a leaf. Hoping that was getting on the intake tube and blocking fuel flow. All cleaned up now.. Gonna re-test later today..

UPDATE 2: Cleaning the tank did nothing to fix the problem.. Mowed for 10 min and started dropping power. If anyone has any ideas, please help.

 

[bertsmobile1]

check that the carb solenoid works and will stop the engine if the kill wires are removed from the magnetos
Do some test mows
Let us know what happens

NOTE
THIS IS FOR DIAGNOSIS PURPOSES ONLY
Using the mower in this condition is so dangerous it is not funny unless you can pick your nose left handed

 

[slomo]

Cleaned fins on cylinder heads, they were packed pretty good.

For one BRAVO.

Do you know, this is a YEARLY, or more often if you bag, maintenance item, in yours, an every other engine manual out there? Neglect the cooling fins and you are asking for engine damage. You should be doing this on EVERY air cooled OPE item you own. Great winter project. Pull engine shrouds off and clean her like she was new.

To me, sounds like either trash in the fuel tank still (lack of fuel delivery) or your new ignition coils are weak. As in getting hot and reducing spark. Your spark needs to jump a 1/4 inch gap in free air. You could have one plug wire with a bad wire or connector adding resistance or several other things.

4 things that engine needs. Air, fuel, spark (at the right time, flywheel key) and compression. Find out which you are lacking.

 

[slomo]

Pressure test the carb needle/seat at 7psi. Should hold for 30 mins.

Pull oil stick smelling stick for gas. Holler here if you smell gas.

Is your choke opening 100% when commanded?

Take an auxiliary fuel tank. See if she runs better.

You need a good spark tester that jumps a large gap. Not the Christmas light kind that blink. Visually see the spark.