John Deere L120 won't rev up

Hey, need advice on this....about ready to throw in towel.

Have a John Deere l120 thats about 7 years old. Has a CV23 Kohler engine 23 HP. Couple of weeks back, it started running very rich and has gotten to where it will crank but will only run at idle and when u rev engine up it will choke out....u can tell it is running extremely rich even with choke off. Below are the things I have done to try to fix but with no luck.

Cleaned carb three times(including the solenoid valve....not a speck of dirt/varnish in it....no effect
tried adjusting carb....turning the mix screw has no effect at all on the engine
removed air filter and tested running with no air filter...no effect
replaced fuel filter, also bypassed filter with no effect
cleaned spark plugs
checked gap on valves
checked to make sure it was getting gas from fuel pump....no issue there
as a last ditch effort, i took a cab from a 78 model john deere 110 and retrofitted it to my l120. mower cranked right up but with same issue, will not rev up.

Any new direction will be much appreciated. out of things to check.