Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Idle issues after rebuild

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ducrider123:
First of all Hello everybody.

So I tried to tackle a qjet by myself for the first time, and it's not going to well.  At idle it smells rich and burns your eyes, I can screw the idle screws all the way in and the engine still runs. Here is some background.

Carb settings. 17080260 m4me
needle seat opened to .125, solid seat
primary jets- .071
primary needles- .052 step up
secondary hanger- M
idle bypass added- I think .050 holoes drilled in the base plate.
mixture screw holes opened to .090
float set at 1/4"
secondary well holes opened to .040
APT setting 2 turns out- set by measuring the location of the primary needle set in the jets.
base bushings are tight.
new fuel filter
base throttle plates adjusted to 90 deg.
secondary plates have 3/8x1/4 slots
all well plugs checked and resealed.


 I have a Pontiac 400 .030 over dished pistons for a CR of 9.2:1. mild cam. vac 15 in wc at idle.

I am having a problem getting the it set from the start. I can screw the idle screws all the way in and nothing changes. If I tip the choke in the engine bogs. here are a few things I noticed. I do have nozzle drip. The power piston is down against the APT. When I look down the front vent I can see the body gasket is wet with gas around the power piston. Removing a non-ported line the engine speeds up (rich). Tipping in the choke slows the engine.

I appreciate any help I could get. If I forgot any measurement let me know I can get them.

Once again thank you for looking.

Cliff Ruggles:
Were the idle tubes removed and cleaned/sized during the "rebuild"?

New float?

It should be quite lean with that jet/rod combination, not rich.  I'd go back to the basics, and install one of our kits with the high flow Viton needle/seat assembly, new flow, complete accl pump assembly, gaskets, etc.

I would also replace the secondary cam/spring, and get a power piston spring, jets and metering rods more closely sized for what you are doing.....Cliff

ducrider123:
Idle tubes were not removed (afraid to), but i used a small piece of wire and cleaaned them really well. (nothing came out) I did not redrill them.

I used a reuild kit form Hygrade. also i have a edelbrock #1920 kit. I used the accerator pump, last night I installed the .149 needle and seat. It has a new seconardy cam spring, and cam from The carb shop.

Float is new. choke pull-off at 2 seconds.

I followed your book the best I could.  Some things I was either "afraid" or not sure what to do, I.E. how big to drill what holes.

ducrider123:
So I had some time at work so I was looking at a spare M4M carb I have. The way I understand the idle circuit is as follows:

-Primary throttle plates can be closed 100%, and engine should run at idle.
-Fuel comes from the bowl throught the main jets to the area blocked by the front well plugs.
-With the throttle plates closed, vacuum pulls on the mixture screw holes sucking the gas up the    idle tubes down the the restriction, throught the idle screws into the engine.

If I am getting nozzle drip that means my throttle plates are open causing fuel to be sucked through the nozzles.

My thinking is that either my idle tubes are plugged (which your eluding to), the restriction is to small, causing me I am running lean. Which in turn is causing me to open the throttle plates to suck gas through the nozzles to feed the engine. Let me know if I am close.

Cliff Ruggles:
Correct on both counts.  If the idle fuel is insufficient, the throttle plates will end up open far enough to pull fuel from the main system to sustain the engine....Cliff

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