Q-Jet Carborator Mechanic Advise wanted - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cypress TX 72 · 11-02-2005, 10:33 PM

I know my truck is running rich, but would that cause it to blow black smoke from the exhaust?
Can someone tell me how to adjust a Rodchester Q-Jet. how many turns out on each adjustment screw.
Help, Please

67chevemall · 11-02-2005, 11:05 PM

Unless it is new or rebuilt with patience, most of the time
it is easier on yourself to get a 4106 or Holley 600 w/bowl kit.

$0.02

kelsfine69 · 11-02-2005, 11:11 PM

Screw all the way in, and if memory serves me correct 2 1/2 - 3 1/2 turns out

leadfoot067 · 11-02-2005, 11:12 PM

yes black smoke will occur when its rich...the 2 screws only adjust the idle mixture....to adjust those youll need a vacume gauge..hook it to direct manifold vacume....then with the motor fully warmed up move the screws in or out to get the maximum vacume at idle...as far as the rest of it goes its very time consuming to try to explain how to mess with the part throttle and full throttle curcuts on a q-jet...i bought a book on q-jets...it helps ALOT to understand these carbs..

67chevemall · 11-02-2005, 11:28 PM

Quote:

Originally Posted by leadfoot067

yes black smoke will occur when its rich...the 2 screws only adjust the idle mixture....to adjust those youll need a vacume gauge..hook it to direct manifold vacume....then with the motor fully warmed up move the screws in or out to get the maximum vacume at idle...as far as the rest of it goes its very time consuming to try to explain how to mess with the part throttle and full throttle curcuts on a q-jet...i bought a book on q-jets...it helps ALOT to understand these carbs..

You bet

I 'd say the they have the most to learn about and the
hardest to tune at first. vaccum gauge is a good tip

cypress TX 72 · 11-02-2005, 11:34 PM

Well, that explains how to set the idle mixture, but how do you lean out the high speed jet(s). Is that done with the long skinny needles that come down from the top?
If so, I'm going to buy a Carter and slap it on.. No holleys for me.. can't afford the endless supply of power valves.
Thanks for the help guys.

jimfulco · 11-02-2005, 11:50 PM

If the Q-jet was running OK before, just fix it or get it fixed. Odds are if it's a recently developed rich condition, it's probably just some trash in the inlet valve or something along that line. If you buy a new carb, you'll have to adjust it, and the Carter carb uses the same jet & hanging rod calibration system as the Q-jet.

MrC1 · 11-03-2005, 12:21 AM

Also, most new Holleys now come with power valve blow-out protection. I agree, too, they're a much simpler design.

Actually, the Q-jets are more fine-tunable than Holleys. It's just that it takes some learnin to know how to do it. Much moreso than it does to tune a Holley.

**Tom Vogel** · 11-03-2005, 11:48 AM

If meory serves me right, there is one or two small freeze plugs on the bottom of these carbs. They tend to get small holes that allow gas to drip through and pool in the intake. That would also cause a rich condition. Remedy... replace them if they are perforated.

truckster · 11-03-2005, 01:01 PM

What Tom said is right, except they're passage plugs from the manufacturing process. There are foam tabs made to fit in there and seal them off, but I've used JB weld with success in the past.

If you don't have a vacuum guage, you can still tune the idle adjustment. With the engine warm, turn the screws in all the way. Now back them out 1-3/4 turns (if you have the carb spec sheet, it might say more or less, but if not, this is a good starting point). Now start the engine and let it idle. Back out the screws evenly about 1/8 turn at a time. The engine speed should increase at first. When you get to the point that the engine speed doesn't increase any more, turn the screws back in 1/8 to 1/4 turn and you're done.

Blazer1970 · 11-03-2005, 06:05 PM

There is a very good chance that it is either the bowl plugs in the bottom of the carb leaking, or that the power valve is stuck open. Pull the carb apart and take a look.

Wrenchbender Ret · 11-03-2005, 07:18 PM

Check the float. These are great carbs. but need to be cleaned up & o-hauled occasionally. The floats are a cork like substance & can soak up gas causeing a high fuel level. Also make shure the primary metering rods go up & down.

kbs71 · 11-04-2005, 07:17 AM

Try this thread http://www.corvettefaq.com/c3/QJetTuningPaper.doc and this one
http://www.73-87.com/7387garage/drivetrain/myqjet.htm or just go here http://www.corvettefaq.com/listing.asp?group=1&sub=11 there's all kind of engine info and other good stuff about chevy tuning.

bejay · 11-04-2005, 07:39 AM

it probably does just need rebuilt if it ever was running ok on this engine just put a kit and float in it and it will probably be fine, alot of times the metering rods will pop up as the plastic retainer no longer fits tight enough to hold them down and you may have to stake the housing slightly to get it to retain the metering rods if this is the problem.
it is a good idea to put some epoxy or jb weld around the plugs on the bottom of the midsection of the carb as mentioned above, they commonly leak wich can cause long cranking times when starting up the vehicle after it sets for a day or 2 as the fuel pump has to refill the carb before the engine will fire up cant say ive ever seen one leak bad enough to cause a rich condition ever but it is still a good idea to help prevent a possible future problem.

11-02-2005, 10:33 PM	#1
cypress TX 72 Saving one 72 at a time!! Join Date: Sep 2005 Location: Cypress, TX Posts: 261	Q-Jet Carborator Mechanic Advise wanted I know my truck is running rich, but would that cause it to blow black smoke from the exhaust? Can someone tell me how to adjust a Rodchester Q-Jet. how many turns out on each adjustment screw. Help, Please

11-02-2005, 11:05 PM	#2
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Re: Q-Jet Carborator Mechanic Advise wanted Unless it is new or rebuilt with patience, most of the time it is easier on yourself to get a 4106 or Holley 600 w/bowl kit. $0.02 __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

11-02-2005, 11:11 PM	#3
kelsfine69 18 Till I Die Join Date: Mar 2005 Location: Alberta, Canada Posts: 1,522	Re: Q-Jet Carborator Mechanic Advise wanted Screw all the way in, and if memory serves me correct 2 1/2 - 3 1/2 turns out __________________ 2011 GMC Acadia 1969 GMC BBC LS7 2007 GMC Crew Duramax 1987 Camaro Iroc 350 Tuned Port Injection 42000Km 1987 Chevrolet Silverado 350 TBI 1987 Chevrolet Silverado 350 TBI(yes 2) Take me drunk, I'm too home...

11-02-2005, 11:12 PM	#4
leadfoot067 horsepower junkie Join Date: Aug 2003 Location: graham, washington Posts: 326	Re: Q-Jet Carborator Mechanic Advise wanted yes black smoke will occur when its rich...the 2 screws only adjust the idle mixture....to adjust those youll need a vacume gauge..hook it to direct manifold vacume....then with the motor fully warmed up move the screws in or out to get the maximum vacume at idle...as far as the rest of it goes its very time consuming to try to explain how to mess with the part throttle and full throttle curcuts on a q-jet...i bought a book on q-jets...it helps ALOT to understand these carbs.. __________________ 67 short wide box,350/700r4/3.73posi 71 olds cutlass "S" mom bought new..12.30s@113MPH

11-02-2005, 11:34 PM	#6
cypress TX 72 Saving one 72 at a time!! Join Date: Sep 2005 Location: Cypress, TX Posts: 261	Re: Q-Jet Carborator Mechanic Advise wanted Well, that explains how to set the idle mixture, but how do you lean out the high speed jet(s). Is that done with the long skinny needles that come down from the top? If so, I'm going to buy a Carter and slap it on.. No holleys for me.. can't afford the endless supply of power valves. Thanks for the help guys.

11-02-2005, 11:50 PM	#7
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Re: Q-Jet Carborator Mechanic Advise wanted If the Q-jet was running OK before, just fix it or get it fixed. Odds are if it's a recently developed rich condition, it's probably just some trash in the inlet valve or something along that line. If you buy a new carb, you'll have to adjust it, and the Carter carb uses the same jet & hanging rod calibration system as the Q-jet.

11-03-2005, 12:21 AM	#8
MrC1 Dork For Days Join Date: Aug 2005 Location: Dallas Posts: 407	Re: Q-Jet Carborator Mechanic Advise wanted Also, most new Holleys now come with power valve blow-out protection. I agree, too, they're a much simpler design. Actually, the Q-jets are more fine-tunable than Holleys. It's just that it takes some learnin to know how to do it. Much moreso than it does to tune a Holley. __________________ 1972 C20, 402/700R4 - My first classic truck, bought in September 2005. 85% transformed from "Farm" to "Cool" status! 1970 Dodge Challenger 440, 4sp (my other toy) 12.67 @ 117 MPH, with a pathetic 2.022 60' 2007 Dodge Charger SRT-8 2008 Cadillac CTS All-American garage, baby!

11-03-2005, 11:48 AM	#9
Tom Vogel 2WD Jimmy Join Date: Mar 2005 Location: Davis County, Utah Posts: 2,565	Re: Q-Jet Carborator Mechanic Advise wanted If meory serves me right, there is one or two small freeze plugs on the bottom of these carbs. They tend to get small holes that allow gas to drip through and pool in the intake. That would also cause a rich condition. Remedy... replace them if they are perforated.

11-03-2005, 01:01 PM	#10
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 8,021	Re: Q-Jet Carborator Mechanic Advise wanted What Tom said is right, except they're passage plugs from the manufacturing process. There are foam tabs made to fit in there and seal them off, but I've used JB weld with success in the past. If you don't have a vacuum guage, you can still tune the idle adjustment. With the engine warm, turn the screws in all the way. Now back them out 1-3/4 turns (if you have the carb spec sheet, it might say more or less, but if not, this is a good starting point). Now start the engine and let it idle. Back out the screws evenly about 1/8 turn at a time. The engine speed should increase at first. When you get to the point that the engine speed doesn't increase any more, turn the screws back in 1/8 to 1/4 turn and you're done. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

11-03-2005, 06:05 PM	#11
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	Re: Q-Jet Carborator Mechanic Advise wanted There is a very good chance that it is either the bowl plugs in the bottom of the carb leaking, or that the power valve is stuck open. Pull the carb apart and take a look. __________________ Tim

11-03-2005, 07:18 PM	#12
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: Q-Jet Carborator Mechanic Advise wanted Check the float. These are great carbs. but need to be cleaned up & o-hauled occasionally. The floats are a cork like substance & can soak up gas causeing a high fuel level. Also make shure the primary metering rods go up & down.

11-04-2005, 07:17 AM	#13
kbs71 71 rustless in texas Join Date: Aug 2004 Location: Houston, TX Posts: 257	Re: Q-Jet Carborator Mechanic Advise wanted Try this thread http://www.corvettefaq.com/c3/QJetTuningPaper.doc and this one http://www.73-87.com/7387garage/drivetrain/myqjet.htm or just go here http://www.corvettefaq.com/listing.asp?group=1&sub=11 there's all kind of engine info and other good stuff about chevy tuning. __________________ "The secret to creativity is knowing how to hide your sources." "No one really listens to anyone else, and if you try it for a while you'll see why" 71 C-10 LWB presently in a perpetual state of disassembly '96 Toyota (my work car) '04 Mustang Convertable (wife's car & other money pit) Latest aquesition and why my trucks still in the garage covered with junk.. 2010 Aqua Blue metallic 6 speed Manual LS3 2SS/RS Camaro (I want one of these in my truck FAQ here VENDORS here SUPPORT THE BOARD here My second favorite SITE

11-04-2005, 07:39 AM	#14
bejay Registered User Join Date: Aug 2005 Location: missouri Posts: 136	Re: Q-Jet Carborator Mechanic Advise wanted it probably does just need rebuilt if it ever was running ok on this engine just put a kit and float in it and it will probably be fine, alot of times the metering rods will pop up as the plastic retainer no longer fits tight enough to hold them down and you may have to stake the housing slightly to get it to retain the metering rods if this is the problem. it is a good idea to put some epoxy or jb weld around the plugs on the bottom of the midsection of the carb as mentioned above, they commonly leak wich can cause long cranking times when starting up the vehicle after it sets for a day or 2 as the fuel pump has to refill the carb before the engine will fire up cant say ive ever seen one leak bad enough to cause a rich condition ever but it is still a good idea to help prevent a possible future problem.



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