Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
throttle plate v.tubes filled
Kenth:
Yellow is fuel, blue is air and red is emulsified A/F mixture mixed in channels and out the nozzles.
Cliff Ruggles:
The long inner brass tubes are nothing more than airbleeds. The size of the hole in the bottom of them varies with application. Some models will even have an additional set of holes in the airhorn next to the tubes. As the fuel is pulled up thru the large passages around the tubes it turns and makes it's exit via the large round nozzles.
The long tubes simply add some air to the fuel before it reaches the large discharge tubes and eventually into the intake and on down to the combustion space.
One can actually leave the tubes out completely and plug the holes if you want to richen up the A/F ratio a bit and are enable to with small tipped secondary metering rods. A few factory carburetors didn't use the tubes at all and we've had several customers that ended up blocking them off when converting to E-85 as it requires about 30 percent more of it that regular pump gas.
For what you are doing I'd leave them in place. I'd also add here that some "builders" recommend shortening the tubes about 3/16" or so to get them up higher in the passages and out of the "short turn" (potential restriction) in the bottom of the main casting . It is said that they can restrict fuel flow to the nozzles if left full length. I've tested that theory and see no benefit anyplace shortening the tubes but it also doesn't seem to hurt anything either........Cliff
F250 Restorer:
Thank you for taking the time to lead me through that. It took me a while to get it, ha ha, but I think the penny has dropped. Cheers.
F250 Restorer:
Either my secondaries are not opening or I just can't feel it. If they are opening I have to say that power-wise I seem lacking. It is as though I'm missing 25% power at the top end. I've checked the secondary cam, the flap spring tension, and disconnected and plugged the vacuum activated lock out.
Any ideas?
Kenth:
Loosen the flap spring tension 1/8 turn until you notice a bog or hesitation at WOT, then tighten 1/8 turn.
Also, you may need richer secondary rods.
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