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stock settings for QJet?

RootBreaker

RootBreaker

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I just got a remanufactured qjet from a local speedshop. nice and clean...
put it on.. got it all running but boggs when hitting throttle, had to turn idle screw way up to get it to even idle... etc..

so no paper came with it. I do not know if they set it to a stock setting.
It has an electric choke and no I didnt grab the model number off of it so will do tonight.

but can someone tell me stock air/fuel screw turns, high idle screw default (think it is under choke)


also there are a mess of plugged vacuum ports so I have pcv hooked up, vacuum advanced hooked up to right side of carb (passenger).... using intake port for brake booster so not carb...

thoughts, help? need to get it driveable as i believe truck is sold.. :whistle:
 
Call the speed shop and find out how it's setup, for what. Bogs, probably too rich.(edit lean) check the pump shot.
Those setting you are asking for there is no default, app dependent.
1600 fast idle on warm engine and 600-700 idle approx
 
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Start with setting mixture screws for best/fastest idle, or you can also set highest vac with a vac gage then reset idle speed.
 
Check your timing and vac line routing, a bog is caused by going lean, either there is too much air or nothing there to spark it.
 
2 turns out on the idle screws for base then dialed in with a vacuum gauge. Also do you have the part throttle hole opened up on the top of the air horn?
 
You mean the adjustable part throttle screw under the Allen head screw?. If so that's for cruise adjustments only (part throttle). Jets/rod combo must be correct first for your engine.

Only 2 turns out the idle
circuits are on the rich side. Can you kill the engine by turning the mix screws all the way in.?
What do you have for an engine, cam?

What do you mean by when I hit the gas, dead stop to the floor or gentle throttle?
 
blazer74 said:
You mean the adjustable part throttle screw under the Allen head screw?. If so that's for cruise adjustments only (part throttle). Jets/rod combo must be correct first for your engine.

Only 2 turns out the idle
circuits are on the rich side. Can you kill the engine by turning the mix screws all the way in.?
What do you have for an engine, cam?

What do you mean by when I hit the gas, dead stop to the floor or gentle throttle?
Click to expand...

Yes that screw, it made a world of difference on how my engine ran... Also on my wallet because it ran like a dirt track car and dumped fuel down but ran clean.
 
Lars is a buffet of info, it's a lot to digest. Book by cliff ruggals is the best book to get. Cliffs highperformance.Com
 
well here is my carb...

http://www.carburetion.com/CarbNumber.asp?Number=17059584

I turned screws out 3 turns... fudged with timing and throttle.. seems better.. slight miss but will get it dialed in more...

so that site says this carb is

It is a R4-M4MC the M4MC is a Hot air side mounted choke Rochester Quadrajet 4 barrel carburetor, which means the choke is located on the passenger side connected to the carburetor and draws hot air from the intake

but it has electric choke... so obviously converted :dunno:
 
Originally 79 350 chevy truck carb. Probably commercially rebuilt so no telling how it's set up. Not much you can due with it without taking it a part. The apt plug is still in there ,not the removable plug on top just fwd of the choke plate for cruise power adjustments approx 2200 rpm.

Can adjust mixture idle speeds , 2ndary flap opening rate and choke . That's about it.

Dist vac can must be working and timing set correct first.

Reset your mix with it in gear if it's an automatic, fully warmed up, choke open. Carefully remember its in gear, block wheels, emerg brake.

What do you mean by bogs? hesitates then goes or just no power?, need a better description. Off idle, Light throttle, heavy throttle, WOT?
How does it idle?

I hate to say it but I think you got a generic remanufactured junk carb made to fit many apps not vehicle specific.
 
I got it to run pretty well tonight but....
If i ease the throttle it will go all the way fine. Straight idle and mash falls on its face... revs up but sounds choppy. One time hitting throttle it burped through carb since it is getting dark saw a big flame shoot out.....

Company I got the carb from said $75/hr max 2 hrs to set timing carb and all of it. May take them up on it....

I dont know what the timing should be set at. I hit it with the light and timing is in the v of last teeth all the way to passenger side.
 
Ill get a video of it later. I dont care if it is a crappy carb as long as it runs and gets through inspection....
 
I think I would let them tune it for $150 and if they can't it's on them. I assume it ran fine with a diff carb.
Even the wrong base gasket can cause problems with a quadrajet.
 
I assume it ran good at one time previously with another carb?..

If not,the slight miss,the "bog" & the blue flame and spit back thru the carb could be anything from a fouled spark plug,timing is off, bad plug wires,or even a dead lobe on the camshaft,which unfortunately is a common dilema on a SBC..usually an exhaust lobe wears down,exhaust cant get out of the cylinder when the valve doesn't open far enough,and the next time the intake valve opens,the exhaust tries going out thru the carb instead..

I've seen so many bad cams on Chevy's I can tell if the cam lobe(s) are flat just by listening to the sound coming from the carb with the air cleaner off it when you floor it..its a gargling type of sound,and sometimes a miss at idle, or popping back thru the carb is apparent when you floor it quickly..
 
I've been thru the cam lobe ordeal also with my 74 and it had no power and would pop thru carb sometimes if I got on it. It idled fine and was ok with light throttle.
I also had a holly 600 that was on it would pop thru the carb no matter what I did to it and that was after engine rebuild and went back to a quadrajet.

That's why I asked if it ran ok before.
 
well it ran just fine with the holley that was on it. I only sold the holley truck avenger here to someone just for emissions purposes. Yes i could have got it through with a carb then put the holley back on it but I didnt want to bother with that ordeal. Figured lets get a qjet, get it running and be done with it...

here it is with open exhaust and holley truck avenger...

:popcorn:

https://www.flickr.com/photos/56197228@N05/13152779664/
 
One cause of a bog when you smash on it from an idle is the secondary air valve opening too soon. on the passenger side of the carb on the secondary air valve shaft there is a spring with two set screws. Its a real pain cause you almost need three hands to adjust it but it sounds like it needs to be tightened up just a bit. Do it just a little at a time until the bog goes away.
 
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