Too Rich

[rcwilbur]

I am working on adjusting a quadrajet on a 1972 402 chevy engine that I recently acquired--the quadrajet appears to be from another donor 17056202.  So far have just replaced a malfunctioning vacuum secondary lock and adjusted to secondary air plate spring a little.  It runs okay but is way too rich.

I put a wideband on the exhaust and it shows the engine is running at about 12.8 AFR at idle.  When I pump the throttle it dips to 11 and then return to 12.8 or so when I hold the RPM constant at about 2000-2500 RPM (while in park).  I plan to drive it and see whats going on at steady cruise, but my wife didn't want to go along and read off AFR for me.

The engine has excellent vacuum pressure--about 20 psi at idle.  I turned the idle mixture screws about a turn in but didn't see any effect on the widband so I stopped.  Perhaps I didn't turn enough. 

It seems as tough it may be the APT Spring??? or the jets are just too big?? Is this something that could be adjusted using the APT screw?  I plan to take the carburetor  apart and rebuild it, but any advice or things to look for would be greatly appreciated.

Thanks,  Carl.

[Cliff Ruggles]

If you don't know the carbs history, get one of our kits for it and completely/correctly rebuild it.  Write down the jet and metering rod sizes while it's apart.  If you take it apart first, I can tell you if they are correct, or we can simply send you what should be there with the kit, and the correct PP spring for what you are doing.

Once it's in perfect working order, re-evaluate the performance in all areas.  Most likely it will be greatly improved.......Cliff

[rcwilbur]

Thanks very much.  I will go ahead and rebuild it and then contact you again about correct jets and rods.

[rcwilbur]

So I took the carburetor apart to see what the rod sizes are and prepare to rebuild it.  I measured the primary rod size with a dial caliper and they look like they were correct for the carburetor (.048 with a .026 tip).  The jet sizes are 76.  One of the rod tips was bent enough so that it was obvious when you looked at it.  Perhaps because of the bend it is not allowing the rod to go fully into the jet opening?  Could the bent tip be causing the rich condition?  In any event it is way too rich with these rods.  The secondary rods are CH and the hanger is a K. 

It looks like the float was a little too high--measured about .35" from the top of the horn.  Everything else looked to be in pretty good condition and it looks like the float was probably replaced fairly recently.

The filter was a little mangled so I will need to replace it.

Would you recommend getting replacement rods and trying it again? The carburetor number is 10756202. 

[77cruiser]

If the rod doesn't go down into the jet it'll be rich. Jets seem big but depends on the main air bleed size.

[rcwilbur]

Thanks.  I think that may be the problem.  Somewhere on the internet I found the specs for this carb and it seems that the jets and rods are the originals.  The car runs extremely rich, especially on the drivers side cylinders.  It runs so rich that it spits black soot on the drivers side. 

I guess I'll start with replacement rods, but I understand that these rods are no longer produced.

[77cruiser]

Cliff probably has them, if not here's a set of 49's.
http://quadrajetparts.com/used-quadrajet-dualjet-primary-metering-rods-049026-early-style-p-2127.html

[Cliff Ruggles]

We don't use or recommend the "K" series metering rods for those large MAB units.  They don't provide enough control of the part throttle A/F ratio.

I would get a set of our .044" metering rods for it, and put one of our kits in it while it's apart, set the float correctly, replace the PP spring and it will be fine......Cliff