Mi-T-M 3,000 PSI Pressure Washer

I bought this powerwasher used from the US military. I suspect that they wrote it off because the gas line from the tank to the carburetor was leaking. I replaced the line and the engine started on the second pull. It is supposed to be a bad ass power washer, up to 3,000 PSI, with the Briggs and Stratton 11 HP Industrial/Commercial engine.

First Question: the engine goes faster and slower every 6 seconds or so, maybe varying speed by 30%. Why would that be the case.

Second question: how would I regulate water pressure on this beast?

Pressure 3000 PSI, flow 4 GPM, washed model # 0w3004MGD. Mi-T-M Corp, 319-556-7484, 800-553-9053

4.0 orifice size. The Equipment Doctor 420-A Roosevelt Rd, Glen Ellyn 630-942-0044

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