Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Power Piston Selection Approach

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ss-truck:
   Thanks I will give that a try in the near future . About how much should I drop down on the jet sizes when I do that ?

Cliff Ruggles:
We use the aluminum APT plug that is found in the airhorn of the later model carburetors.  The aluminum plug is the perfect size to drop down in the power piston bore, and easily removed later if needed.

Reduce the jet size about 5-7 numbers when removing the power piston and primary metering rods, this is usually a good starting point......Cliff

ss-truck:
   Thanks , can't wait to try that one.  If it changes the mid range driveability , not worried about that .

Hotrodrobert:
Makomark, do you have good stainless props??  I have seen big improvements over alumionum props and in getting just the right prop.
I have several metering rods to fit your carbs if they are the Mercruiser version.  Bigger rods will lean the part throtle and still give you the mixture richness to get on plane.  If you go too small on the jets you will have more trouble getting on plane, load decreases after planing.

makomark:
Robert:

I could probably get Cliff to silver plate both carbs for what a pair of stainless wheels go for sized for my boat. Aluminum isn't an option as these are inboards, not stern drives. The ones on there now are bronze; we've had nibral on and not noticed any performance difference. What did make a difference was the propscan process; essentially a computerized dial indicator hooked up to a turntable. Lets the prop mechanic measure thte prop and then accurately check it as he works it. Not cheap but one of the few items that 'performed as advertised'.

The engines were crusaders, as installed, but when overhauled, all the marine replacement parts came from the Merc warehouse. The carbs were swapped out for Merc versions even before that as we had saltwater in the fuel and it sat all winter.....very ugly inside. Used the crusadder sized jets and rods, which were richer than the Merc selections; best as I could tell, both had the 8"-4" power piston spring. I'm certain that all of the marine q-jet parts swap, at least the internals, and that they are the "pre-170" style, even though the casting numbers indicate otherwise. How "deep" is your primary rod collection?

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