Running diesel/oil blend to flush it out will break all of the gunk and lamination up in the crankcase and oil journals etc. As it'll dissolve it gradually it won't just knock a big chunk of it out and lodge it somewhere else to cause grief. The problem with additives like seafoam or mystery oil is it won't clean the backs of valves like people expect it to (oil flush won't either but it won't turn your engine into a smoke machine while running) If the pick up screen is clogged - I mean really clogged, it'll need to be removed and mechanically cleaned. If you think your combustion chambers are carboned up you can take the throttle body intake pipe off and spray water into the throttle body while the engine is running with a trigger pump sprayer (water has to be atomised and not shot into the intake in a stream) When you hear a 'crackling' sound, the carbon is swelling up and lifting off and getting burnt in the process. Has to be done when the engine is at operating temps.