Now we are getting somewhere, Top. The pressure washer does not have any facility that should cause your engine to drop to idle speed - it should run at the speed you set with the control lever, regardless of conditions. If it doesn't, there is a problem in the engine, or the pump is seizing up or otherwise overloading the engine.
My pressure washer has a screwdriver adjustment of the engine's governed speed. It is readily accessible, but the manual does not mention it or refer to adjusting it, and I don't see why anyone would do so except as a tuning procedure, to suit a specific way of using the machine. I don't know why Troy Bilt had an adjustment lever on your governor - they will have had a marketing reason rather than a technical reason I think.
It does sound at the moment as if your engine has a small malfunction. I suggest we move forward as follows:
1. Please post the Model, Type and Code numbers for your engine. They are usually on a sticker on the cooling air cowling somewhere, but there are other places they sometimes put them. The Model number will probably start with 12 and have a total of 6 characters. The Type will have 4 characters, a dash, and two more characters. The Code will have 8 characters. The three numbers (Model, Type and Code) will all be together. When I have those numbers I can refer to the Operator's Manual, Illustrated Parts List, and workshop manual for accurate details of the engine.
2. Provided the engine is still bolted down to the frame of the pressure washer, it is safe to start and run it without the pump attached. I think it will be considerably easier to proceed that way, both to check that it still misbehaves without the pump attached, and then if it does, to diagnose and fix the exact problem.
3. At the moment it sounds as if you have a governor malfunction on the engine. This may be as simple as something jamming the linkage from the speed control lever to the governor plate near the carburetor, or it may be that a lever on the governor plate has become bent, or the governor spring has fallen off. Then again, it may be something else.
