strange engine issue from 900-1400 rpm

[swamp rat]

Remove the air cleaner (engine off) then pull one of the air fuel screws all the way out and take a can of carb cleaner with the spray nozzle and stick it in the hole till it bottoms out, open the chope plate and throttle plate and look down the carb, give the carb cleaner a couple short sprays and see of you can see any carb cleaner spraying into the venturi, if not the port is plugged, repeat in the other side.

I have had the crap fuel we get today gum up and clog idle fuel the ports after just sitting for a while, i can usually just give the ports a shot of cleaner and clear them out.

I agree you could have a vacuum leak but i think you are compensating for the lack of fuel thru the idle circuts by screwing the idle screw on the linkage in too much thus opening the throttle plates too much and pulling the mix from the off idle circut.

[Clavo106]

ok my friend.my 2 cents.. if its engine in searching at idel i would looking for a Frist vac leak. then timing... now iv never rebuild a q jet but I have rebuilt plenty of motorcrafts... I few years a go I had similar experiences with a friends of Cadillac he bought a eldbroc carb and slap it on left it seting for a few years and ask me to get it running.. I got it fired up thru it in drive ran for a bit then died. when I thru it in reverse admittedly died.. I did everything . look and adjust timing about more time I could count sprark. vac leaks spark. coil dis.... and how many time I adjust the A/F screws a bout a hundred time it did not change a thing.... I finely gav in and told him if he had the original carb he said he did.. so I slap that bad boy on and worked solid. drove great.. not saying it would work for u but im thing looking at that carb another time would not hurt.. good luck..

[Bocephus69]

i removed both a/f screws.


drivers side (the side i know works) - if i blow air into the a/f screw hole, it will geyser fuel out of a small, vertical hole on the front of the carb. whe blowing carb cleaner into the screw hole, i get a light mist of vapor inside the carb below the choke flapper.

passenger side - when i blow air into the a/f screw hole, i dont get a geyser, but i get a mist inside the carb. spraying carb cleaner into the a/f screw hole yields about the same results as the drivers side....a light mist of vapor inside below the choke flap




i took some small wire and cleaned out what i could. resprayed air, resprayed carb cleaner, put the a/f screws back in and i have no change at all.



i talked to another guy that asked if i replaced these when i rebuilt the carb. i said no. what are you thoughts? http://quadrajetparts.com/idle-picku...ice-p-291.html

[Bocephus69]

also, would the choke have anything to do with this? could the dial on the passenger side be in an incorrect place? or doesnt it matter how that's set once the engine is warm (the choke flapper is all the way open once engine is warm)

[Bocephus69]

Originally Posted by Redline novdog

If it were me would pull the carb off and run some tag wire through all the passages and blow air through afterwards. Check your primary throttle shaft for play(worn) also.

this shaft has play. i ran the engine and sprayed carb cleaner on the passenger side (where the roll pin goes trough the shaft to hold it in), and i do get a slight rpm change. it is barely noticeable, but no doubt it is sucking in a little air there.

[Redline novdog]

Sounds to me like one side of the idle circuit is blocked. Could be as simple as one of the new gaskets didn't get a hole punched correctly,or sludged up from sitting.The best way to clean a carb is in the agitator bucket of carb cleaner, and I have seen crap still stuck in the small passages.
Yes you can replace the tubes,these don't just fall out,or drop in. so if you go that route make sure you have adequate tools.
Unless your wanting the experience and fun of working on a Quadrajet,at this point I wold buy a rebuilt one.

[Redline novdog]

Forgot ( its to early) You can also purchase throttle shaft bushing kits to do away with the play in the throttle plate and shaft

[Bocephus69]

Well I got the carb completely apart and cleaned before I had to go to work this evening. I found nothing obvious, but still used a lot of carb cleaner and compressed air. I did a little research about float height, and plan to set/check it tomorrow before reassembling the carb

[Bocephus69]

well guys, i got this 350 purring like a kitten. as i mentioned above, went through all the fuel/air passages again with carb cleaner and compressed air. i didnt find/see anything that threw a red flag at me, but who knows....i could have had a blockage someplace.


one thing i did do some research on was float level. i found some interesting info. i found that pre 1975 carb float levels are set at a different height than 75+ models. well, when i rebuilt the carb, the kit's instructions said to set the float at 5/16ths (.312).


now, the 350 in this pickup was a donor from a 76 caprice. the info i found online suggested setting 75+ q-jets float in the .400-.410 range.....so thats what i did.


i fired this baby up, and knew right away something changed. constant rpm idle, less engine vibration. i put it in gear with the foot on the brake, and it runs PERFECT with a load on it. no more vibration, no more resonating sounds in the cab that make your ear drums hurt (haha).


i set it for 35-36* total timing, which put me at about 11-12* initial. the idle a/f screws are about 2.5 turns each (and yes both work now). i love it when things work out as planned

[Sklptrljay]

Always nice when an annoying problem like that goes away!

[Redline novdog]

SCORE!!!!! Good job! And thanks for the update!