[oldbluesplayer]

the trash in the gas is the key - that may have come from the bum fuel filter you already replaced, or it may have come from the tank, and gone by the bum fuel filter -

either way, having replaced the fuel filter, Everything upstream, from the filter, thru the pumps, into the carbs, needs to be cleaned out now. That should get the engine running smoothly again...

But you still need to find out what caused it - mostlikely need to clean and purge the tank, and the lines.

As to the engine pulling 5000 rpm no load - not surprising - I've run motorcycle for many years, they are much the same, engine wise, with no load, you can hit red line with just a quarter throttle, but it won't take any load like that without bogging right down.

Anyways - it's critical to get the gas system cleaned out all the way - if a piece of residual dirt, downstream of that new fuel filter, gets into the carb, and partially blocks the main jet, your engine will start running lean, and then trash the powerhead in short order - bad carburation is the fastest trip to a seized engine.

Bill