Generac QS 7.5 Shutting down after "hunting" or "surging"

Jon Daneri

New Member
Sep 2, 2019
2
Boat Info
1992 400 EC
Engines
Twin 454 Mercrusier
I know questions on this generator have been beat to death, but I have been pouring through the posts on the forum and I can't seem to find my specific issue previously posted.

My QuickSilver Generator 7.5G starts fairly easily and runs smoothly. Handles the load of both AC units and with a new impeller and recent cooling system flush, has a good flow of water out of the exhaust.

The problem: If I start it when the engine is cold it will run for a period of time, sometimes several hours before it begins "hunting" or "surging" with rapid throttle fluctuations for about 15 seconds before shutting down. If I try to immediately restart, it will crank but not stay running. If I let it sit for an hour or so, It will start again and run for a shorter while, maybe an hour before shutting down.

Question: If it is overheating...would it "hunt" or "surge" like this before shutting down? I assumed that it would just turn off if it overheated. If it is not overheating, what would cause it to behave this way after running smoothly for several hours?

Thanks to all in advance the information I have learned from this forum has been invaluable.

Jon
 
How long have you had the boat?
If the condition just started review any changes recently made in the area of the generator.
Sounds like a fuel starvation condition associated with vapor lock. Is the fuel supply routed close to a heat source?
Try insulating the fuel line.
 
How long have you had the boat?
If the condition just started review any changes recently made in the area of the generator.
Sounds like a fuel starvation condition associated with vapor lock. Is the fuel supply routed close to a heat source?
Try insulating the fuel line.

I purchased the boat this past April, not sure what maintenance other than a recent oil/filter change has been performed on it. Ran the generator during the pre-buy survey, but not long enough to see any issues. I also replaced the exhaust hose, but the problem existed before & after the replacement. I'll have to check the fuel line...so what your saying is that you think that some of the fuel is vaporizing in the lines when the generator heats up causing fuel starvation?
 
That is my initial thought given that after a hour or so of cooling down the generator starts and runs normally.
Most auto part stores sell insulation that will keep the fuel line and fuel cooler.

If that doesn’t fix the problem the check the fuel pump and check for spark as ignition coils are also affected by heat.
 

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