QuestionI have some small problem. I in the middle of process rebuilding MIKUNI BS34 carburetors. The piston valve stuck
inside the carb. Have using WD40, carb-cleaner and also kerosene, however it won't get free. Is there any other method that i can use to free the piston valve.
AnswerI'm not entirely sure what you mean by "piston valve" (maybe the carb slide?), but I think the answer will be the same anyway.
Try using a quality penetrant (AKA penetrating oil). PB Blaster is the best one I've tried yet.
I would soak it in solvent for a half hour or so first to remove any residue from the WD40. My first choice would be mineral spirits, but methanol would probably work too.
And put the WD40 away until you need to displace water from somewhere, because that's all it is good for. That's what the name means: Water Displacer 40th attempt at a formula that works. It's basically a light fish oil, and it has several interesting properties, among which are that it freezes at -20c (no good in locks), when the solvent evaporates it leaves a sticky residue that attracts dust (no good for cleaning contacts), and it is biodegradeable (washes away with water - no good as a lubricant). It is good for loosening duct tape, however.
