carburetor problem with my JD 1020
I'm having a carburetor problem with my JD 1020. Couldn't get it running, found there was no fuel in the carb so I checked the needle valve and found that it was stuck and not allowing gas to come in. Got it working and put it back together and now can make the gas come in but can only make it run at just a little more than an idle. Must be the high speed jet, but I can't understand how it operates. Why is it on an electric solenoid. Does anyone know the function of it and why is it there in the first place? I've adjusted it according to instructions in the owners manual and can't seem to hit the right spot to give the tractor any power.