adjusting idle screws on a qjet - The 1947 - Present Chevrolet & GMC Truck Message Board Network

crm318 · 01-21-2007, 03:17 AM

the weather is very cold here and my truck runs really bad at idle. i unscrewed the idle mixture screws about half a turn and it ran good for a while and then did the same thing after sitting a day. what do yall think? which way do i turn the screw the screws to get more fuel at idle....if thats the right thing to do?

lilpup69chevy · 01-21-2007, 03:44 AM

be a lot cooler if you got rid of that qjet LOL j/k

**WorkinLonghorn** · 01-21-2007, 09:50 AM

Have you tried adjusting the choke? That sounds like the issue to me.

crm318 · 01-21-2007, 10:06 AM

well, it is a divorced choke and it doesnt work with my rpm intake...so i dont have one. however, the choke is completely open. the truck will run like crap for the first 10 min of driving even with the heater blowing hot.

68speedalert · 01-21-2007, 10:17 AM

Quote:

Originally Posted by crm318

well, it is a divorced choke and it doesnt work with my rpm intake...so i dont have one. however, the choke is completely open. the truck will run like crap for the first 10 min of driving even with the heater blowing hot.

That's what is going to happen without a choke. The engine needs more fuel, the colder it is. After running for 10 minutes, (depending on temp) the choke isn't needed as much,

The ONLY way you normally adjust the mixture screws is after the engine is COMPLETELY warmed up.

Start by seating each one and opening the same amount (do this engine off), maybe 3 1/2 turns. Start the engine and open each screw 1/2 turn. Listen if the engine speeds up. Keep doing that until the RPM's don't increase. Now turn the screws in 1/2 turn at a time until the rpm's just start to fall. Open each screw another 1/2 and your done. You could open another 1/2 since your choke isn't working...might help a little.

Now when the engine cools off again, it's gonna run like crap until it's warm again. Live with it or fix the choke.

BTW, the farther from stock your engine is, the worse it will run when cold.

Sport/Truck · 01-21-2007, 10:24 AM

Or you can use the above method using a vacuum gauge and adjust until you get max vacuum.
s/t

Rokcrln · 01-21-2007, 10:27 AM

My Father in-law did my carb yesterday (Holly

) and how he did it was simular to above but he had me hook up a vac guage to the intake and he set the idle screws untill he got the highest vac posible. We were able to get 19.5 in lbs of vac at idel and it runs great! My choke is not hooked up yet but it will be once I buy the elect choke conversion kit. Good luck. also when turning the screws go about a 1/4 to a 1/2 turn at a time and let the motor idel for a bit between adjusting.

Kevin
LFD Inc.

piecesparts · 01-21-2007, 10:31 AM

The idle mixture screws are just that (they provide a stable air/fuel mixture for the idle), they do not provide an idle speed. The choke governs the need to add more fuel to control the idle during a cold start. This is designed to make the motor run rich at that time so that it will overcome the cold temps. You could adjust your normal idle screw up to hold the motor at a higher idle speed, BUT it would idle like that at all times (not good), so unless you fix your choke you will always have cold start problems. Since you are running a carb that is not attached to either the intake for control, or a hand choke, or an electrical choke, the problem continues. I would look at upgrading to either an electrical connection and install the electric choke kit or put a hand control on it. I imagine that Edelbrock still has the conversion kits for that, since it is a performer Q-jet.

lilpup69chevy · 01-22-2007, 03:55 AM

edelbrock does make a kit to convert the divorced style choke to an electric choke i'm wanting to say as a matter of fact i think mark aka rage n rat was talkin about that the other day might wanna ask him he probably has a part number i'd say fix the choke then set the carb

sixtysevengmc · 01-22-2007, 05:57 PM

only thing an old Q jet is fit for is a doorstop

68speedalert · 01-22-2007, 06:20 PM

Quote:

Originally Posted by sixtysevengmc

only thing an old Q jet is fit for is a doorstop

Only for those not smart enough to fix em......

vfrdude · 01-22-2007, 06:22 PM

Quote:

Originally Posted by sixtysevengmc

only thing an old Q jet is fit for is a doorstop

I suppose automatic transmissions, and disk brakes are junk, too....

68speedalert · 01-22-2007, 06:57 PM

low sierra · 01-22-2007, 07:00 PM

Quote:

Originally Posted by sixtysevengmc

only thing an old Q jet is fit for is a doorstop

Mine works great and get pretty good mileage.

cooters · 01-22-2007, 07:05 PM

bow down to the q jet, once you figure them out, they are the best carb ever made for daily driving and 450hp and under motors

*rage'nrat638* · 01-22-2007, 08:29 PM

heres the edelbrock convertion kit and a few pictures

i will get here sooner or later..i am slow in my old age

crm318 · 01-23-2007, 01:37 AM

will i need to find a carb that has the heated choke to use the conversion choke? my carb has nothing on that side of the carb and i dont see anywhere to mount one. as for the qjet, i think that general motors is the best and i think that they only go with the best parts.

68speedalert · 01-23-2007, 02:25 AM

You are correct, your qjet must have the heated choke for that kit to work. You still have the correct still carb for your truck. Look for one from a 70's model full-size GM car or late 70's GM truck.

The bigger the engine the better. You've got a good enough engine that a larger qjet would help it run better.

You could get a manual choke conversion for your carb, but they rarely work very good.

chopper103in · 01-23-2007, 10:24 AM

manual chokes work great as long as the person running it knows what they are doing

68speedalert · 01-23-2007, 11:16 AM

Quote:

Originally Posted by chopper103in

manual chokes work great as long as the person running it knows what they are doing

......AND the person installing it knows what they're doing.....

OEM manual chokes always work good, conversions are not as good; brackets are never strong enough for one thing.

piecesparts · 01-23-2007, 05:43 PM

How about a pic of your carb, showing the choke area and let's see what is up.

crm318 · 01-24-2007, 10:13 PM

i would but im the only guy in the world that doesnt have a digital camera. however. i do remember when i got it from the parts store, it was for a 72 chevy. there are no areas on the passenger side of the carb that would be able to mount a heated choke. its only cold for a month or so here in texas and im thinking about buying junkyard carb with the proper set up and rebuilding it before next winter.

piecesparts · 01-24-2007, 11:06 PM

It is now that I would start looking at installing a manual choke cable.

71cheyennezz4 · 01-25-2007, 02:49 AM

Eh quadrajunk..... i suggest this www.barrygrant.com

68speedalert · 01-25-2007, 12:05 PM

Quote:

Originally Posted by 71cheyennezz4

Eh quadrajunk..... i suggest this www.barrygrant.com

Only if you like a much more expensive Holley.....not for me.

01-21-2007, 03:17 AM	#1
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	adjusting idle screws on a qjet the weather is very cold here and my truck runs really bad at idle. i unscrewed the idle mixture screws about half a turn and it ran good for a while and then did the same thing after sitting a day. what do yall think? which way do i turn the screw the screws to get more fuel at idle....if thats the right thing to do? __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies

01-21-2007, 03:44 AM	#2
lilpup69chevy 67-72 parts finder Join Date: Aug 2006 Location: southeast mo Posts: 788	Re: adjusting idle screws on a qjet be a lot cooler if you got rid of that qjet LOL j/k __________________ 1969 chevy shortstep 2wd (under construction) 1981 chevy scottsdale lwb 2wd (parts chaser) 2004 pontiac gto (daily driver) 2004 pontiac grand prix gt (the ol ladys car) 1985 chevy short wide 1970 chevy c10 lwb (another parts rig) 1969 gmc lwb (rainy day project) 1968 chevy lwb c10 250 I6 3 spd (soon to be swb)

01-21-2007, 09:50 AM	#3
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,886	Re: adjusting idle screws on a qjet Have you tried adjusting the choke? That sounds like the issue to me. __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

01-21-2007, 10:06 AM	#4
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: adjusting idle screws on a qjet well, it is a divorced choke and it doesnt work with my rpm intake...so i dont have one. however, the choke is completely open. the truck will run like crap for the first 10 min of driving even with the heater blowing hot. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies

01-21-2007, 10:24 AM	#6
Sport/Truck Sierra Grande Club Join Date: Jan 2007 Location: New Mexico USA Posts: 2,433	Re: adjusting idle screws on a qjet Or you can use the above method using a vacuum gauge and adjust until you get max vacuum. s/t __________________ 1971 GMC Sierra Grande, 1/2 ton short wide, original 4 bolt 010 020 block & heads. (matching #'s). 383 stroker, SMI q jet 750 cfm, Lunati Voodoo 60102 cam, Scorpion roller rockers, Spin Tech pro street mufflers with X pipe.

01-21-2007, 10:27 AM	#7
Rokcrln Senior Member Join Date: Jul 2005 Location: Winters Ca. 95694 Posts: 4,843	Re: adjusting idle screws on a qjet My Father in-law did my carb yesterday (Holly ) and how he did it was simular to above but he had me hook up a vac guage to the intake and he set the idle screws untill he got the highest vac posible. We were able to get 19.5 in lbs of vac at idel and it runs great! My choke is not hooked up yet but it will be once I buy the elect choke conversion kit. Good luck. also when turning the screws go about a 1/4 to a 1/2 turn at a time and let the motor idel for a bit between adjusting. Kevin LFD Inc.

01-21-2007, 10:31 AM	#8
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: adjusting idle screws on a qjet The idle mixture screws are just that (they provide a stable air/fuel mixture for the idle), they do not provide an idle speed. The choke governs the need to add more fuel to control the idle during a cold start. This is designed to make the motor run rich at that time so that it will overcome the cold temps. You could adjust your normal idle screw up to hold the motor at a higher idle speed, BUT it would idle like that at all times (not good), so unless you fix your choke you will always have cold start problems. Since you are running a carb that is not attached to either the intake for control, or a hand choke, or an electrical choke, the problem continues. I would look at upgrading to either an electrical connection and install the electric choke kit or put a hand control on it. I imagine that Edelbrock still has the conversion kits for that, since it is a performer Q-jet.

01-22-2007, 03:55 AM	#9
lilpup69chevy 67-72 parts finder Join Date: Aug 2006 Location: southeast mo Posts: 788	Re: adjusting idle screws on a qjet edelbrock does make a kit to convert the divorced style choke to an electric choke i'm wanting to say as a matter of fact i think mark aka rage n rat was talkin about that the other day might wanna ask him he probably has a part number i'd say fix the choke then set the carb __________________ 1969 chevy shortstep 2wd (under construction) 1981 chevy scottsdale lwb 2wd (parts chaser) 2004 pontiac gto (daily driver) 2004 pontiac grand prix gt (the ol ladys car) 1985 chevy short wide 1970 chevy c10 lwb (another parts rig) 1969 gmc lwb (rainy day project) 1968 chevy lwb c10 250 I6 3 spd (soon to be swb)

01-22-2007, 05:57 PM	#10
sixtysevengmc village idiot Join Date: Oct 2006 Location: Barbourville,KY Posts: 176	Re: adjusting idle screws on a qjet only thing an old Q jet is fit for is a doorstop

01-22-2007, 06:57 PM	#13
68speedalert Semi-Senior Member Join Date: Feb 2003 Location: Washington, MO Posts: 390	Re: adjusting idle screws on a qjet __________________ '68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab

01-22-2007, 07:05 PM	#15
cooters Senior Member Join Date: Oct 2006 Location: Edmonton Alberta Posts: 458	Re: adjusting idle screws on a qjet bow down to the q jet, once you figure them out, they are the best carb ever made for daily driving and 450hp and under motors

01-22-2007, 08:29 PM	#16
rage'nrat638 Account Suspended Join Date: Mar 2003 Location: THE FALL GUY CHICAGO IL Posts: 5,883	Re: adjusting idle screws on a qjet heres the edelbrock convertion kit and a few pictures i will get here sooner or later..i am slow in my old age Last edited by rage'nrat638; 07-12-2007 at 06:58 AM.

01-23-2007, 01:37 AM	#17
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: adjusting idle screws on a qjet will i need to find a carb that has the heated choke to use the conversion choke? my carb has nothing on that side of the carb and i dont see anywhere to mount one. as for the qjet, i think that general motors is the best and i think that they only go with the best parts. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies Last edited by crm318; 01-23-2007 at 01:39 AM.

01-23-2007, 02:25 AM	#18
68speedalert Semi-Senior Member Join Date: Feb 2003 Location: Washington, MO Posts: 390	Re: adjusting idle screws on a qjet You are correct, your qjet must have the heated choke for that kit to work. You still have the correct still carb for your truck. Look for one from a 70's model full-size GM car or late 70's GM truck. The bigger the engine the better. You've got a good enough engine that a larger qjet would help it run better. You could get a manual choke conversion for your carb, but they rarely work very good. __________________ '68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab

01-23-2007, 10:24 AM	#19
chopper103in Registered User Join Date: Dec 2006 Location: sycamore,il Posts: 163	Re: adjusting idle screws on a qjet manual chokes work great as long as the person running it knows what they are doing



Register or Log In To remove these advertisements.

01-23-2007, 05:43 PM	#21
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: adjusting idle screws on a qjet How about a pic of your carb, showing the choke area and let's see what is up.

01-24-2007, 10:13 PM	#22
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: adjusting idle screws on a qjet i would but im the only guy in the world that doesnt have a digital camera. however. i do remember when i got it from the parts store, it was for a 72 chevy. there are no areas on the passenger side of the carb that would be able to mount a heated choke. its only cold for a month or so here in texas and im thinking about buying junkyard carb with the proper set up and rebuilding it before next winter. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies

01-24-2007, 11:06 PM	#23
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: adjusting idle screws on a qjet It is now that I would start looking at installing a manual choke cable.

01-25-2007, 02:49 AM	#24
71cheyennezz4 Registered User Join Date: Mar 2006 Location: York Nebraska Posts: 64	Re: adjusting idle screws on a qjet Eh quadrajunk..... i suggest this www.barrygrant.com __________________ http://www.cardomain.com/ride/2269113 http://classictruckworld.tenmagazine...ry.ten?id=3895

Register or Log In To remove these advertisements.