The power valve is located on the fuel inlet to the mixer on the underside of the inlet is a rich/lean adjustment.....you rev the engine to full speed and put it into tilt bypass and adjust the power valve.....is best to do it with a CO gas analyzer but know not everyone has one........to clean just remove the mixer from the truck and remove the diaphragm from the top of it and spray a rag down with a good cleaning solvent and wipe out the inside of the mixer good and can use air to blow it out.