Flooding at idle

[Scott]

      Got a problem here fellas, hoping for some help.....
Car: 1966 Impala 327/275 hp PG, 90k, bone stock, never been apart. Carb: 7028212 (68 327, same specs), should be good match.
      Sent to Cliff in March for work. Primary throttle shaft was rebushed, bottom wells replugged, fuel inlet Heli- Coiled, and cleaned and recolored. New float/accelerater pump/needle & seat (all from Cliff's) installed.
      The problem: carb is overloading at idle. It runs good "on the move", but can't get a good idle out of it. It is obviously flooding, hand over choke area makes it worse. I checked fuel pressure-steady, just under 6 p.s.i. at idle. Float set at 5/16". Checked power piston w/screwdriver thru vent, is bottomed out at idle. Cannot see any "drips" in carb while running (including secondaries). With carb apart, hooked up vertical line tube & tested needle/seat with gas in bowl: could not blow thru line. There is no leakage outside carb.
     Any thoughts?

[Cliff Ruggles]

If it were "flooding" fuel would be running out of the boosters, accl pump shaft hole, and even the front vent if the flooding were bad enough.

Sounds rich at idle.  How is the idle system set-up?  Idle tube size, downchannel restrictions, etc?....Cliff

[Scott]

    Cliff, I don't have precision bits to measure the idle tubes. I did fit a 1/16" bit (slightly loose) into the idle "up" tubes. Thought I had a factory "unmolested" carburetor here, but, maybe not. Checked a spare 7028212 I have, 1/16" bit will not fit. BTW, primary jets are #71, primary rods are #46B (factory specs, according to Lars Grimsrud at digitalcorvettes.com). What's the turnaround time to fix this problem, if I send it to you?....Thanks, Scott....

[Cliff Ruggles]

The restriction in the idle tubes is at the bottom on the small end, not at the top.

Currently, we are BURIED in carb work, and not able to add anything to the pile.

If the carb runs great everyplace but at idle, go back thru the idle system to make sure everything is where it needs to be for sizing, including the idle tubes, upper idle airbleeds, lower idle airbleeds, and idle down channel restrictions.

The jet/rod relationship is fine, the larger 46B rods were raised up by the APT screw in the baseplate to fine tune the part throttle A/F ratio.....Cliff

[Scott]

   Sorry for the delay, been rounding up tools. Here are the specs (approximate, but very close): idle tubes .038" (replaced with .036" tubes from Cliff"s); idle down channel .050; upper idle air bleed (bowl) .079; lower idle air bleed .060. Mixture screw channels .080, no idle air bypass.
   After replacing the idle tubes & blowing out the fuel inlet area for good measure, I replaced the carb using an old manifold gasket that blocks off the exhaust crossover holes (previous one had crossover channel open). Car is now running GREAT, smooth idle, good power & mileage - like a Quadrajet should!   
   All I know about the intake is that it is a pre-69 (big oil fill tube in front) Chevy model. Could the exhaust crossover have caused the rich idle? Anyway, thanks for all your help, Cliff...Scott...
       

[Cliff Ruggles]

Yes, well, it will have a big effect on idle quality, as it's a HUGE vacuum leak unless completely sealed off with the correct gaskets.....Cliff