I have removed the PCV system from the carb to breathers and would like to clean the carbs without removing them. They are 850 Nickerson holleys on top of 177 superchargers. Can I use regular carb cleaner or do I pose a risk of blowing something up with the compresion of the charger? The carbs have oil residue around the venturi and plates.

the best thing to do is merc makes an injector cleaner that you put in the fuel system that works pretty well,that way you get every thing clean not just the venturies and throttle plates

Also, pull the idle bleed screws, spray thru them, note which air bleeds the spray comes thru (watch your eyes) and then spray down thru these bleeds. Keep throttle closed in case red tube pops off carb cleaner nozzle. Do this a few times - ie: thru bleed screw holes, then thru idle bleed holes. Proceed to spray thru the other air bleeds.

Cleaner in gas tank will not clean these 'dry' circuits out.

I recommend doing this atleast 2 times each year. Minimum when coming out of and going into storage. Middle of season would be smart too.

These idle bleed circuits are crusial for drivability + power.

I've found that Sea Foam works pretty darn good too.

Sb speaks the truth !!!!

but short of rebuilding you could also pull the fuel bowls replace the power valve ect