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Hank F.
Hank F. , Technician
Category: Small Engine
Satisfied Customers: 14365
Experience:  Certified on Onan and Generac generators
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I have a Generac modle 004582 (15000watt) 32 horsepower gas

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I have a Generac modle 004582 (15000watt) 32 horsepower gas engine. Start fine, runs for about 45 min. when hot out , then turns off. It will start up for a few seconds and turn off. If it sets for about a hour it starts and runs fine till it gets hot and turns off. Unit has maybe 30 to 40 hrs. on it

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This one could prove to be one that is not able to be remedied without actually being able to see it, but I will give it a try.


The fact that it will start back up tells me that is most likely not ignition related - but we need to keep that option open.


My first thought is that it may be suffering vapor lock.

Is the fuel line routed too close to the engine or exhaust manifold?

One thing you could try to rule out or confirm vapor lock is to install a fan that blows on the carb and fuel line. If the set will continue to run with a fan blowing on it, we have most likely found the problem.


Another possibility is a bad fuel pump.

To test it, let the genset get hot, and shut it down.

Immediately remove the fuel line from the carburetor and place it into an empty container.

Crank the engine for a few seconds and watch the fuel flow. This will not have a particularly strong stream, but it should be 'pulsing' as the engine cranks.

Does it appear to have enough fuel flow?


Another possibility is that the stepper motor controller is overheating and shutting the set down.

Here is how to test it:



1. When you click on the link below, a new web page called 4shared will open.

2. When 4shared opens, scroll about half way down the page until you see a BLUE ‘Download Now' button on the left side.

3. Click on the BLUE ‘Download Now' button. Do not click on any GREEN buttons.

4. Clicking on the BLUE button will start a 20 second timer.

5. When the timer expires, a BLUE link that says ‘Download Now' will appear directly above the timer.

6. Click on the blue ‘Download Now' link above the timer to start the download.


Click here to download the file.


If none of this finds the problem, let me know and we can check some other things.


Hank F., Technician
Category: Small Engine
Satisfied Customers: 14365
Experience: Certified on Onan and Generac generators
Hank F. and other Small Engine Specialists are ready to help you
Customer: replied 5 years ago.
Hank This has a impulse pump on the valve cover on one of the heads. It has about 1 inch of air space under it. I have checked the flow before,but after it cooled down. Do you think i should replace the impulse pump ?

Yes, I realize it is an impulse pump.

The issue could be (just a thought - no guarantees), that if the diaphragm is getting too hot, and getting too soft, it may not be stiff enough to pump fuel.

Another possibility with it is if the engine crankcase is loosing vacuum/pressure for whatever reason, it may not be able to drive the pump.


It is not a very expensive part, but I personally would not change it unless it tests bad.


Customer: replied 5 years ago.
Hank would a inline electric fuel pump help if this is the problem ?
Customer: replied 5 years ago.
a reply to - would a inline electric fuel pump help if this is the problem ?

You know, I really couldn't say - I've never been asked that, and have never had a reason to check.


But, I would doubt it. The problem would be the fuel pressure.

The pulse pump has virtually no pressure to it - maybe 1-2 psi?

I'm not sure of you could find an electric pump that would guarantee that low of a pressure.

Too much pressure and you will blow the seat out of the carb.


Customer: replied 5 years ago.
Thanks for your help Chuck

Not a problem.

Let me know what you find.


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