Engine won't rev up as high on full throttle Kohler CH20OS Toro Groundmaster 120

Its 1 Kohler CH20OS 624CC   spec 64555, serial 2726715917. Toro Groundmaster 120
The throttle is pushed up to full throttle but it doesn't seem to be as high as it was. If I push on the
Govenor arm it revs up. There seems to some adjustment that is out of wack. I replaced the spring going to that
arm in the picture.   I have a new fuel pump and filter and spark plugs. It seems to startup fine and run fine but
just not able to get more RPMs in the full throttle position??????
 
When I kick the blades in they don't come up to full speed like they use to a few weeks ago. Something is acting
strange here. If I push on the Gov arm where that spring is in the picture the rpms come way up like they use to.
 
What do you think is wrong here????????????????  Hope someone can help.

I checked the cable in full throttle position and tightened it. Im adjusting this screw and locknut in the third picture and it seems to be making a difference.
I wonder is there adjustments that can be made to the carburetor is there a carburetor on this engine twin Vee that can be adjusted. It might have been awhile since its been adjusted?????
 
I found a service manual online and that screw with locknut is the highspeed adjustment screw looks like from
what I read.
 

Yes run good. The high speed adjustment screw might need adjusting. I found that in the service manual online.
https://www.manualslib.com/manual/700336/Kohler-Ch18-745.html?page=44#manual
 
I turned it some and it seems to be helping. Will play with it later today.
 
 

Ground the spark to each cylinder. I supect one is dead.

Remove the spark plug wire to one cylinder at a time then stick a screwdriver into the terminal and lay the shank against a metal surface. If nothing changes that cylinder is not producing power. If the engine quits the other cylinder is not working.

I haven't tried the screwdriver into the spark plug terminal yet. I just wonder why do that and not just pull
the sparkplug wire while engine is running and see if engine quits if Im looking maybe for a bad Ignition Coil on one of the cylinders.
Im sure there is a reason for the screwdriver placed against some metal while the engine is running.
 
Just wonder about that.
 

But it is a good feeling to to get hit 12-15Kv. Getting hit 35Kv is even a better feeling.

Well don't seem to have power to the front plug.  If I unplug the front plug the mower will still run.
If I unplug the back plug and plug in the front plug it will not run.  I guess the front plug is not getting
in power.  The ignition coil for it must be bad.  
The question is how do I get to the coil under the cowling on the Toro GroundMaster 120. Has anyone replaced
a coil on one of these. There is not much room between the side and the cowling to pull out.
 
 

You may have to remove the engine to access the coils.

As Roy hinted at you may need remove the engine just to get to the coils. I got a few riders here like the old shaft drive Cub Cadets where the engine has to partially come out to get to coils. Glad they don't fail very often but one of the reason the 2T engine crane here though I need a gantry type instead, my back just won't let me do this heavy lifting anymore.
 
Yes 2T is overkill but I need it for auto engines and lifting of ZTRs when pulling transaxles assemblies. The Z925A is especially a pain as both has to come as one assembly.