People the above portable unit is powered by a briggs & stratton engine model # 257412.
Ever since the unit was new this problem presisted, despite being to the supplier a few times ( my dad got fed up with them after seeing no results ... but that is history now ).

The initial problem was that the exhaust manfold used to get red hot after about 1 hour of runnning and the speed would start to change from high to low but the unit would not stall.
( the unit is rated 8000W and was used to power 10 twin tube 10feet flourscent lamps and 4 computers with LCD displays. The computers ran on UPS for when switchover to generator is done ).

It was sent back under warranty and all I see was done is that they drill a hole in the gas cap. This issue with red exhaust disappeared but the varying speed still comes.

This evening I ran it and after approx 30 mins the speed issue returned.

Correct plug was replaced and regapped according to specs, fuel filter replaced, air filter replaced,all throttle/ choke linkages lubricated and checked for free movement.
Oil replaced with specified body.

The unit gives no problem to start , one pull and it starts but after a while the speed problem returns resulting in a severe variation in output voltage. (120 v to 90 v).

Removing the loads results in same problem.

People who repair these units any suggestions.

Is the speed going hi low an hi again? if so u may have a faulty load spring that fails when the engine gets hot, or the fuel cap on the tank is not breathing well enough try cracking the cover a tiny bit when the problem starts n c if it goes away. Let me know how it turns out.

littleshotter, the initial problem was that the exhaust manifold by the muffler used to get red hot and speed problem after about 1 hour. What the company did under warranty was to drill a hole in the fuel cap. This sorted the initial problem but then the speed problem returned.
Will try cracking the cover.
The spring is attached to a lever with multiple holes, dont want to move it to another hole since from the limited info I got this is a govenor and I would not want to risk over running the engine.

Drilling the hole in the fuel will have the same effect as cracking the cover.

cracking the cover problem did not go away , removed it same thing

I encountered a similar problem on a honda generator...

I found out through troubleshooting that the float in the carburetor reservior pan was sticking... there is a spring located in there as well, if the spring is sticking the the float will not operate properly causing the engine to loose rpm/power...

Its worth a try... let me know the outcome..

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moderation is key
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did you get through with the problem?

_________________
moderation is key
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will look at this this weekend, thanks