Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Setting up the new carb--pointers?
F250 Restorer:
I have a newly rebuilt QJ from 78. I kept all the settings, mix, idle, secondaries that it was set at for a sbc. I did change the m. rod piston spring to one with more tension since it is going on a 309 ci ford I6.
I'm hoping someone here would be so kind as to give me a basic step by step guide with this. I've worked on carbs before, but this is by far the most complicated. I'd appreciate any help offered.
Thank you.
Cliff Ruggles:
Stronger springs simply start the power piston up earlier when engine vacuum drops off sharply. In most cases, use the strongest spring that will have the power piston down at idle, as it will get it moving up the earilest and quickest when you hit the throttle hard, or any situation where the engine needs more fuel.....Cliff
F250 Restorer:
I installed the rebuilt today. Although I disconnected the choke, and the idle screw is all the way backed out, I can't get the idle to drop to normal. First off I tried to adjust the mix, and there was no difference whether all the way in or out. So I snipped off a rung of the springs, and now it starts to shutter when all the way in. I assume I should snip off another bit? The engine should die when all the way in, right? Also, I'm guessing it is idling at about 1200 rpm, minimum, and surging. When I try the 'tip in' it speeds up, so I think it is lean?
Normally I would think vacuum leak with the idle staying up. Tomorrow I will spray around the crab with starting fluid, and see if I have a leak.
Help is GREATLY appreciated.
F250 Restorer:
I also found this and wondered if someone could explain it: Don't try to set the idle without holding the hot idle compensator tang back on the back of the carb.
Cliff Ruggles:
I would block the HIC hole and not use it. Just another potential vacuum leak at idle.
The engine should idle down, if not, too much idle bypass air, vacuum leak, secondary throttle plates not seated well in their bores, etc.
The mixture screws may not kill off the engine when seated, as some fuel is delivered thru the exposed portion of the idle transfer slots at idle speed. Turn the screws in till it just slows the engine, back them up about 1/2-3/4 turns, should be pretty close for idle mixture settings.....Cliff
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