Idle issues after rebuild

[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

[ducrider123]

I figured it out.
problem - When I looked down the vent when the engine was running I could see gas on the top of the gasket, as well as a little gas around the accelerator pump shaft. I figured I had the float to high causing the engine to flood. So I took the carb apart lowered the float a little. While I had it apart I pulled the idle tubes. Daunting but got them out. I then fallowed your recipe #2. reassembled it, and it runs great. I have full adjustment with the idle screws out 2.5 turns.

The difference from a Edelbrock 650avs to the Quadrajet is unbelievable.  The power difference when the secondaries kick in is amazing. 

I do have one question. 

When I go from idle to WOT I have a hesitation.  I had it with the Edelbrock also but a lot worse.  If I don't hit it "hard" it pulls really hard no hesitation.  I am assuming it is a momentary lean condition.  Should I be looking to add a stiffer power piston spring, or tighten the secondary spring? It is at 3/4 turn. Also the secondary plates have notches in them.

[Shark Racer]

The difference from a Edelbrock 650avs to the Quadrajet is unbelievable.  The power difference when the secondaries kick in is amazing. 

You shouldn't feel the secondaries kick in... you may be able to hear it, but you shouldn't be able to feel it.

I do have one question. 

When I go from idle to WOT I have a hesitation.  I had it with the Edelbrock also but a lot worse.  If I don't hit it "hard" it pulls really hard no hesitation.  I am assuming it is a momentary lean condition.  Should I be looking to add a stiffer power piston spring, or tighten the secondary spring? It is at 3/4 turn. Also the secondary plates have notches in them.

3/4 turn should be pretty tight, but you may try going a little tighter. Is your choke pulloff hooked up and effective? (does it hold a vacuum?)

Do you really mean "idle to wot" or "cruise to wot" or...?

[ducrider123]

Yeah, good point. I have my kickdown set so that when the secondaries open the trans kicksdown.  Poor choice of words I guess. Correction: The power difference from the AVS to the Qjet is dramatically different.

The choke pull off does hold a vac and it is set at 1.5-2 sec release.

Maybe it is because I am use to 350 chevy's, and I have been able to go from idle to WOT without a bog.  But ever since I have been working on my pontiac I have had a bog. The AVS was really bad. no matter what I did it stumbled really bad. (Dan at the tech center knows me quite well from all of my conversations with him.) The Qjet is a dramatic difference. If I just stand on it bogs for 1 sec then it recovers and launchs. If step into it transitions great.  I know it's a lot to ask for a reaction from the carb but I was wondering if it could be improved.

[Cliff Ruggles]

Even the slightest hesitation/stumble/bog going to full throttle indicates that there is either a momentary rich or lean condition.  The Q-jet is easy to tune.  I'd start with the accellerator pump and check ball, making sure there is a good seat at the check ball, and put a good pump in it.

The Edelbrock accl pumps are JUNK, as are most of the pumps from over the counter kits.  The "blue" seal they use is soft and doesn't hold up or work well with this new fuel.

The springs they put on and under the pump are incorrect, and will cause the problems you are seeing.

The choke pull-off release time/rate, and secondary spring tension are also a player.  There should be no play in the linkage going from the pull-off to the secondary airflap shaft.

The POE system is a player here as well.

In almost all cases, when we see carburetors that are causing problems when the driver goes quickly to full throttle, it's just a matter of minor adjustments and some better parts....Cliff