I have a Kohler model: 6.5MCCK
that worked fine last season. I just tried starting this season and
it starts fine but dies once the start switch is released. The
manual says it could be a sensor problem. Is there a way to bypass
the sensors to test the generator? It will run as long as I hold
the start button. Any ideas?
Like Old Houseboater said, the oil pressure would be a good first place to start. Because there isn't any oil pressure when you first try to start the switch is bypassed as long as you hold the start button, so if there isn't any oil or if the switch has failed the symptom you describe would be the result.
First verify the oil level, then jump across the the oil pressure switch. The oil pressure switch in this application is a little different than the type used to light an "idiot light", which has only one connection and is normally "closed". The oil pressure switch on the generator should have two wires on it and is "normally open". If you jump across the two wires (or remove them from the switch and connect them together, or connect both wires to one contact) you will bypass the switch.
If the generator starts and runs then shut it down immediatly! Do not continue to run the generator unless you can verify that you do indeed have oil pressure. You could remove the oil pressure switch and replace it with a gauge, threading it directly into the block if it is in a place where you can see it. I wouldn't leave the generator in this configuration, replace the switch ASAP.
If it isn't the oil pressure then I would guess that the generator isn't generating, or it isn't converting any of the 110 volts AC to 12 volts DC that the control logic needs.
If you generator is like the one I used to own the control logic only draws power from the battery when you hold the start switch. Once the engine starts and the generator produces power a small amount is rectified and dropped down to provide a trickle charge to the battery and run the control logic.
You should be able to get an indication of the generator output by observing the AC while you are still holding the start button. Plug an AC lamp into an outlet, if the lamp lights then the generator is working. If the lamp doesn't light then the problem will be in the generator, either the brushes or control logic.
If the AC lamp does light then I would suspect the circuit that converts a small amount from 110 AC down to 12 VDC. My generator had a BIG resistor that was used to drop the voltage, mounted directly in front of the cooling fan. That resistor failed and with it so did the generator.
When you remove the lid from the control box look on the inside of the cover to see if they still are putting the schematic for the control logic there. It can be a tad difficult to decipher but all the information you need is there.