RV Repair: Generator Repair, control circuits, generator repair

Question
I am working on my Onan Emerald III Genset.  I have read alot about my problem and have narrowed it down.  The problem: while depressing the start button the Genset seems to run fine.  When I let off the start switch the unit dies.  The carb is getting fuel, the oil sensor has been checked, getting spark etc.  I think I'm down to the control board or the voltage regulator.  Question:  Is there a way to determine if either part is good?  Or, which is more likely the fix?  Or, do I buy both parts figure out which is the culprit and keep the other part for backup?

Answer
Hi Todd:
There are a lot of these problems lately, must have answered 5 or 6 in the last month. Sounds like you are deep into it. When you push the start button many things in the control circuits are bypassed. Couple of things to try. Once you let go of the start button all these safety and control things become active. The first is the governor. The engine starts full throttle and then the governor takes over to keep in from running away with itself. If the governor does not the throttle closes and the engine dies. You can manually grab the throttle rod and if you can keep it running that way the governor is bad. The next thing to look at is spark. You may have it fine when you are crancking but lose it when you try and run. I run a seperate hot wire to the coil to see if you can keep running that way. If it stays on then the board is probably bad. Have somebody check the output voltage while you run it holing the start button in. Just do this for a short time, it will not hurt the starter as it kicks out when the engine starts whether you are on the button or not. This will check the voltage regulator. My guess is you have a problem with the board or the governor.
Good luck.
Bill