I have a Torro Lawn Tractor, with a 20 HP Kohler Engine.
I am having a problem with the engine,in that it wont run unless the
Throttle is wide open and the choke
is about three quaters closed. With the choke in this position and the
Throttle set
all the way open, the engine will run. However it will not reach full
Rpm's
being in this manner. Also the engine does not appear to be
mis-firing.
So far I have changed the fuel filter,and the fuel pump.
There is suction in the vacume line going to the fuel pump,however, I
don't know how strong it should be.
The vent in the gasoline cap is OK,The air cleaner on the carburetor
is OK,I even tried running the engine without any air cleaner, but it
made no difference.
I made sure the carburetor was set to the settings in the "Kohlers"
owner's Manual. I also added fresh gasoline to the tank.The spark
plugs were changed in May of this year.
The Toro tractor is about 3 years old with about 60 hours on it.
Here are the Kohler Engine Specifications: Model No. CV20S
                                           Family No. SKH624UIG2RB
                                           Spec. No. 65531
                                           Displ. (CC) 624
                                           Twin Cylinder

 Thank for your help.

With lawn mowers, I have found turning the unit upside down to drain
the tank completely before adding fresh gas sometimes helps.   Neil

It sounds to me that because it requires that the choke be on during
full throttle that the engine isn't getting enough fuel. Purhaps the
jet in the carb is partly clogged, that would create a "starving for
fuel" problem. Also,if it has a timing belt on it, it might have
jumped a tooth or two so that the timing isn't correct anymore. I
would guess that it is a fuel problem rather than a timing problem.
Have you tried spraying carb cleaner down the throat of the carb? The
carberator may need rebuilding.  If you feel comfortable doing it you
can try and spraying gas out of a spray bottle down the throat of the
carb while it is running to see if the engine speed increases. Be very
carefull doing this, you don't want to start a fire. Start slowly and
try and not flood the engine while spraying the gasoline. Also, have
the choke open when you do. You might want to check the float bowl in
the carb for dirt and make sure that the needle valve is properly
adjusted and that there is gas in the bowl. I sounds like a carb
problem to me. Good luck.