Some generators have a rpm governor that controls the output voltage.
Sounds like yours is one of those and it's sticking open too far. When
you add a load the engine throttle gets opened further to keep the rpm
constant. When the load is removed the engine throttle is not being
backed off thus the increase in speed and voltage.

wrote:
Greetings,

I have a Westerbeke 4.0KW gas genny in my boat, and I'm experiencing
the following: The genny runs like a sewing machine, and when first
started, the voltage settles right at 115. When a load is presented
(A/C for example), I'll get the typical drop from the load while the
genny adjusts, and then the genny will settle back to around 115. All
is well at this point. The problem is, when the load is removed (when
the A/C cycles), the voltage rises to 150 and stays there. I notice
an increase in engine speed as well.

My initial thought is that the voltage regulator might have gone
south, but I don't know if this would explain the rise in engine
speed. I guess if the regulator doesn't control the voltage, the
engine speed will rise accordingly to satisfy the higher voltage, but
I'm no electrical engineer, so it's just a guess.

Any input would be greatly appreciated! I'm planning an anchor-out
this weekend, and with the rains and heat/humidity in FL, I can't be
without A/C!!!