I boil everything. Carburetors,fuel petcocks,exhaust pipes,baffles,everything. Clean it first with solvent and warm soapy water,or pressure to remove the bulk of loose material. Make sure there is no gasoline or other flamable materials left. Be careful of which of your wifes best pots to use,and boil! Solvents other than real,volatile,carb cleaner will often not clear the laquered,varnished,clogged passages in carbs,etc. It may loosen and temporarily soften the material,but then it often will not come out of the passages and quickly re-blocks them. laquer thinner can do the same. The extreme heat of boiling afterward seems to do the job for me,"personally",every time. There is a concern of melting or warping plastic / neoprene parts. I've never had a problem,but try to remove all these parts beforehand if possible. Also rubber parts swell,but contract again when cool. If the rubber is dried and cracked when you start,it will be dried,cracked,and potentially ruined just like other methods when your done. After boiling,you will then need to re-clean the part with carb cleaner or solvents to remove the left over residue. Scared yet? Mark.