How the heck do you adjust a Q-jet?!? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Syco67 · 07-26-2004, 10:21 AM

Working on my sisters 69 3/4 GMC, and it seems to be running a little rich. I was gonna adjust it, but I can't find the screws. I noticed two holes on the front at the base of the carb that appeared to have little tiny bolts inside. Is that where you adjust it? Do you need some special tool to do it? How much does this carb flow, it will need to be replaced soon as it appears to be leaking fuel from the secondary shaft onto the manifold. I don't want to over/under carb it. It's the stock 350 4-bolt, the Q-jet looks original too.

Fred T · 07-26-2004, 12:25 PM

Go to this website for info http://www.carbs.net/carbinf.htm

You have a major problem with the shaft leak. It will need to be bushed to fix it. With the stock 350, a 600 cfm holley or edelbrock will make a good replacement, they usually work good right out of the box with idle and mixture adjustment.

silvertonguedevil · 07-26-2004, 12:27 PM

A friend of mine and I just rebuilt the one on mine. If your carb is running rich, I would start with the idle mixture screws. There are two screws in the front of the carburetor (down low by the base-plate). Those screws should be turned in all of the way and then backed off approx 1 1/2 to 2 turns (depending on elevation). The other issue you might have is the float level may be off. The only way to adjust that is to take the carb apart. Once you've gone that far you might as well rebuild it. I would say that that fuel leak is a pretty major issue too. You may need to replace the carb all together to fix that.

shuttermutt · 07-26-2004, 02:40 PM

The procedure is as follows:

- Remove the linkage, vac hoses, etc.
- Remove the four bolts at each corner of the base
- Install Edelbrock part number 1406

Sorry, I couldn't resist.

I know that Q-Jets can be set up to run mean and miserly, but there's just too much black magic involved for my tastes. I love my 1406 for its (occasionally) brutish simplicity.

67ChevyC10Stepside · 07-26-2004, 02:55 PM

i agree with shutter......you tune one by buying an edelbrock.

silvertonguedevil · 07-26-2004, 06:15 PM

I'm gonna have to go ahead and go with the flow on this one. I have had a lot of Q-jets and though they all seem to work ok , none of them ever seemed to be awesome. Even after rebuilding mine, I'm not happy with it. I know a lot of it probably has to do with my carburetor skills

but still....

Gordo · 07-26-2004, 07:59 PM

Those adjustment screws may have a special head on them requiring a special tool. If that doesn't work try a 12oz ball-peen from Sears.

FirstGen · 07-26-2004, 08:36 PM

my Q-jet put down 340 RWHP on a 305 LOL... but run a 1406 if you want I've used those too. The 1406 is great for the street and is OK at best at the track.
just my .02

MACKL · 07-26-2004, 09:00 PM

Shuttermutt, you left out one very important step,

The procedure is as follows:

- Remove the linkage, vac hoses, etc.
- Remove the four bolts at each corner of the base
- Install Edelbrock part number 1406
- Give old Q-jet to MACKL

I made a very good living rebuilding those things for about 8 years.
I'll take every one I can get and smile all the way to the bank!
LOL...Kelly

Jimmy72custom · 07-26-2004, 09:18 PM

Some of the air/fuel mixture screws on the smog Quadrajets had plastic limiting covers. When you break them off to adjust past the limit, you would find weird looking screws, but you can still turn them.

ChevLoRay · 07-26-2004, 10:51 PM

Hey, MACKL!!

Didn't he mention some little bitty screw heads??? Wouldn't that be a later model Q-Jet?? Seems like I remember those "mod-Quads" having the base metal caps that had to be broken off to get to the idle air screws (that we weren't supposed to touch) and finding those small screw heads. I'm thinking the early Q-Jets had larger heads on the screws....much easier to get a screwdriver on.

I like my Edelbrock 1901 Q-Jet. I've still got a 1405 Edelbrock and an Edelbrock rebuild kit for it. Just can't decide whether to fix it and sell it, or just keep hanging on to it and wait til I need it and then rebuild it. Anyway, it don't cost nuthin' to let it set, does it?

Oh, I like Q-Jets, but they are very easily mis-understood. They have a few quirks, but when they're right, they're awesome.

MACKL · 07-26-2004, 11:47 PM

ChevLoRay,
You are correct. GM's first attempt at limiting the adjustment on the Idle air fuel adjusitng screws was to install plastic limiters that would pop off with a sharp wack on the end of a long screwdriver. Some time in the mid to late 70's, they switched to a hardened steel cap that were embeded in to the aluminum base plate. They also changed up the screw heads, the first was one you could turn with a screwdriver, the second was a screw head similar to the letter U, but top of the U looked just like the bottom. I think the actual term is a double D. (The lower part of our steering shafts have the same shape). The third was simply a 3/16" hex, except you woul have to grind the sides down on your socket before it would fit in the hole. You can buy a flexible cord tool that has both of the most common adjusters, one on each end. They shoud be sold at all of the major parts stores.

Syco67,
It is almost impossible to properly diagnose a carb via message board. The adjustments at the front base of the carb only adjust the IDLE air fuel mixture.
If you have fuel leaking out of the secondary throttle shafts, adjustment wont help. A carb works just like a toilet, except there is no handle to jiggle! Either you have a float level extremly too high, (splashing over the side), a float that is soaked with fuel causing it to be heavy, (allowing the needle and seat to seperate), or simply trash in between the needle and seat. All of which are easy to fix if you are carb savy. A nightmare if you are not.
If you have any questions, please let me know. Good luck...Kelly

shuttermutt · 07-27-2004, 12:38 AM

Quote:

Originally Posted by MACKL

Shuttermutt, you left out one very important step,

The procedure is as follows:

- Remove the linkage, vac hoses, etc.
- Remove the four bolts at each corner of the base
- Install Edelbrock part number 1406
- Give old Q-jet to MACKL

I made a very good living rebuilding those things for about 8 years.
I'll take every one I can get and smile all the way to the bank!
LOL...Kelly

Hey, I never said that a Q-Jet couldn't be built hella stout. I've seen several that were really fine carbs. For the average Joe, however, I'm a big fan of the Edelbrock simply because they're simple, they perform well, and anybody with a modest tool kit (including a set of Torx) and an afternoon to kill can rebuild one with great success.

jimfulco · 07-27-2004, 03:17 AM

Sometimes you can slip a short length of tubing over the bolt heads & turn the tubing like a handle.

Syco67 · 07-27-2004, 09:47 AM

It only leaks when the truck is turned off, and it only does it once in a while, not every time. Won't spill a drop while it's running though. I think it is rich cuz I get a decent amount of black smoke when I blip the throttle. I know some is normal, and when driving in 100* temps, in stop and go traffic, it feels like it is bogging slightly, and will blow quite a bit of black smoke upon even moderate accleration. The engine isn't overheating or anything either. An edelbrock carb is in the future, just needed to know the right size, and 600cfm seems to be the way to go.

kbs71 · 08-06-2004, 02:30 AM

Try these links
http://www.corvettefaq.com/c3/QJetTuningPaper.doc
http://www.73-87.com/7387garage/drivetrain/myqjet.htm

nate68 · 08-07-2004, 05:27 PM

adjust it with your credit card....... by buying an edelbrock carb

07-26-2004, 10:21 AM	#1
Syco67 Registered User Join Date: Jan 2004 Location: Boise Posts: 64	How the heck do you adjust a Q-jet?!? Working on my sisters 69 3/4 GMC, and it seems to be running a little rich. I was gonna adjust it, but I can't find the screws. I noticed two holes on the front at the base of the carb that appeared to have little tiny bolts inside. Is that where you adjust it? Do you need some special tool to do it? How much does this carb flow, it will need to be replaced soon as it appears to be leaking fuel from the secondary shaft onto the manifold. I don't want to over/under carb it. It's the stock 350 4-bolt, the Q-jet looks original too. __________________ If at first you don't succed, break something!

07-26-2004, 12:25 PM	#2
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	Go to this website for info http://www.carbs.net/carbinf.htm You have a major problem with the shaft leak. It will need to be bushed to fix it. With the stock 350, a 600 cfm holley or edelbrock will make a good replacement, they usually work good right out of the box with idle and mixture adjustment. __________________ Fred There is no such thing as too much cam...just not enough engine.

07-26-2004, 12:27 PM	#3
silvertonguedevil Senior Member Join Date: May 2004 Location: Seaside, Oregon Posts: 1,789	A friend of mine and I just rebuilt the one on mine. If your carb is running rich, I would start with the idle mixture screws. There are two screws in the front of the carburetor (down low by the base-plate). Those screws should be turned in all of the way and then backed off approx 1 1/2 to 2 turns (depending on elevation). The other issue you might have is the float level may be off. The only way to adjust that is to take the carb apart. Once you've gone that far you might as well rebuild it. I would say that that fuel leak is a pretty major issue too. You may need to replace the carb all together to fix that. __________________ -Greg My Chevy trucks, past and present: 1962 C10 SB Fleetside 1964 C10 LB Fleetside BBW 1966 C10 SB Fleetside 1966 C10 SB Fleetside BBW 1968 C10 SB Fleetside 1971 C10 LB Fleetside 1971 C10 SB Fleetside 1972 C10 SB Fleetside Cheyenne 1972 C10 SB Fleetside Cheyenne Super 1972 C10 LB Fleetside Cheyenne Super 1974 C20 Cheyenne 1979 K5 Blazer Cheyenne 1982 K10 SB Fleetside Custom Deluxe 1982 K10 SB Fleetside Scottsdale 1986 C10 SB Fleetside Silverado 2008 Silverado 1500 4x4

07-26-2004, 02:40 PM	#4
shuttermutt Don't say "Oops!", Doctor Join Date: Nov 2003 Location: Houston, TX Posts: 677	The procedure is as follows: - Remove the linkage, vac hoses, etc. - Remove the four bolts at each corner of the base - Install Edelbrock part number 1406 Sorry, I couldn't resist. I know that Q-Jets can be set up to run mean and miserly, but there's just too much black magic involved for my tastes. I love my 1406 for its (occasionally) brutish simplicity. __________________ 'Mutt 1968 CST LWB: R.I.P. 1967 Chevelle: TPI 454 beast 1967 C10 SWB: Claimed when Bumpster didn't put it on his list

07-26-2004, 02:55 PM	#5
67ChevyC10Stepside Registered User Join Date: Mar 2004 Location: Butler PA Posts: 3,032	i agree with shutter......you tune one by buying an edelbrock. __________________ 67 c-10, 400 SB, TH350, 4.10 gears, Blazer tank,camaro tach, sidemarker fuel fill (soon) WTB: stepside parts, 67 front end parts, 67 small window cab. posi for 3.73 or 4.10 for 12 bolt and 10 bolt.

07-26-2004, 06:15 PM	#6
silvertonguedevil Senior Member Join Date: May 2004 Location: Seaside, Oregon Posts: 1,789	I'm gonna have to go ahead and go with the flow on this one. I have had a lot of Q-jets and though they all seem to work ok , none of them ever seemed to be awesome. Even after rebuilding mine, I'm not happy with it. I know a lot of it probably has to do with my carburetor skills but still.... __________________ -Greg My Chevy trucks, past and present: 1962 C10 SB Fleetside 1964 C10 LB Fleetside BBW 1966 C10 SB Fleetside 1966 C10 SB Fleetside BBW 1968 C10 SB Fleetside 1971 C10 LB Fleetside 1971 C10 SB Fleetside 1972 C10 SB Fleetside Cheyenne 1972 C10 SB Fleetside Cheyenne Super 1972 C10 LB Fleetside Cheyenne Super 1974 C20 Cheyenne 1979 K5 Blazer Cheyenne 1982 K10 SB Fleetside Custom Deluxe 1982 K10 SB Fleetside Scottsdale 1986 C10 SB Fleetside Silverado 2008 Silverado 1500 4x4

07-26-2004, 07:59 PM	#7
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	Those adjustment screws may have a special head on them requiring a special tool. If that doesn't work try a 12oz ball-peen from Sears. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

07-26-2004, 08:36 PM	#8
FirstGen Just Don't Stop! Join Date: Feb 2004 Location: Dallas Posts: 1,239	my Q-jet put down 340 RWHP on a 305 LOL... but run a 1406 if you want I've used those too. The 1406 is great for the street and is OK at best at the track. just my .02 __________________ 1968 C10 build in process TT LSA/6L90e/9"

07-26-2004, 09:00 PM	#9
MACKL Almost done! Join Date: Apr 2004 Location: Woodstock GA Posts: 193	How to Adj. a Q-jet Shuttermutt, you left out one very important step, The procedure is as follows: - Remove the linkage, vac hoses, etc. - Remove the four bolts at each corner of the base - Install Edelbrock part number 1406 - Give old Q-jet to MACKL I made a very good living rebuilding those things for about 8 years. I'll take every one I can get and smile all the way to the bank! LOL...Kelly __________________ The 1970 SWB Project Removed 6cyl manual trans, manual everything V8-350 Auto/PS/PDB Blazer Fuel Tank Behind the Marker Light Fuel Fill

07-26-2004, 09:18 PM	#10
Jimmy72custom Registered User Join Date: Apr 2004 Location: Willits Ca Posts: 261	Some of the air/fuel mixture screws on the smog Quadrajets had plastic limiting covers. When you break them off to adjust past the limit, you would find weird looking screws, but you can still turn them.

07-26-2004, 10:51 PM	#11
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Hey, MACKL!! Didn't he mention some little bitty screw heads??? Wouldn't that be a later model Q-Jet?? Seems like I remember those "mod-Quads" having the base metal caps that had to be broken off to get to the idle air screws (that we weren't supposed to touch) and finding those small screw heads. I'm thinking the early Q-Jets had larger heads on the screws....much easier to get a screwdriver on. I like my Edelbrock 1901 Q-Jet. I've still got a 1405 Edelbrock and an Edelbrock rebuild kit for it. Just can't decide whether to fix it and sell it, or just keep hanging on to it and wait til I need it and then rebuild it. Anyway, it don't cost nuthin' to let it set, does it? Oh, I like Q-Jets, but they are very easily mis-understood. They have a few quirks, but when they're right, they're awesome. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

07-26-2004, 11:47 PM	#12
MACKL Almost done! Join Date: Apr 2004 Location: Woodstock GA Posts: 193	ChevLoRay, You are correct. GM's first attempt at limiting the adjustment on the Idle air fuel adjusitng screws was to install plastic limiters that would pop off with a sharp wack on the end of a long screwdriver. Some time in the mid to late 70's, they switched to a hardened steel cap that were embeded in to the aluminum base plate. They also changed up the screw heads, the first was one you could turn with a screwdriver, the second was a screw head similar to the letter U, but top of the U looked just like the bottom. I think the actual term is a double D. (The lower part of our steering shafts have the same shape). The third was simply a 3/16" hex, except you woul have to grind the sides down on your socket before it would fit in the hole. You can buy a flexible cord tool that has both of the most common adjusters, one on each end. They shoud be sold at all of the major parts stores. Syco67, It is almost impossible to properly diagnose a carb via message board. The adjustments at the front base of the carb only adjust the IDLE air fuel mixture. If you have fuel leaking out of the secondary throttle shafts, adjustment wont help. A carb works just like a toilet, except there is no handle to jiggle! Either you have a float level extremly too high, (splashing over the side), a float that is soaked with fuel causing it to be heavy, (allowing the needle and seat to seperate), or simply trash in between the needle and seat. All of which are easy to fix if you are carb savy. A nightmare if you are not. If you have any questions, please let me know. Good luck...Kelly __________________ The 1970 SWB Project Removed 6cyl manual trans, manual everything V8-350 Auto/PS/PDB Blazer Fuel Tank Behind the Marker Light Fuel Fill

07-27-2004, 03:17 AM	#14
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Sometimes you can slip a short length of tubing over the bolt heads & turn the tubing like a handle.

07-27-2004, 09:47 AM	#15
Syco67 Registered User Join Date: Jan 2004 Location: Boise Posts: 64	It only leaks when the truck is turned off, and it only does it once in a while, not every time. Won't spill a drop while it's running though. I think it is rich cuz I get a decent amount of black smoke when I blip the throttle. I know some is normal, and when driving in 100* temps, in stop and go traffic, it feels like it is bogging slightly, and will blow quite a bit of black smoke upon even moderate accleration. The engine isn't overheating or anything either. An edelbrock carb is in the future, just needed to know the right size, and 600cfm seems to be the way to go. __________________ If at first you don't succed, break something!

08-06-2004, 02:30 AM	#16
kbs71 71 rustless in texas Join Date: Aug 2004 Location: Houston, TX Posts: 257	Try these links http://www.corvettefaq.com/c3/QJetTuningPaper.doc http://www.73-87.com/7387garage/drivetrain/myqjet.htm



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08-07-2004, 05:27 PM	#17
nate68 Registered User Join Date: Jan 2000 Location: ca Posts: 1,110	adjust it with your credit card....... by buying an edelbrock carb __________________ 68 short step, 406/700r4, 9" w/discs.

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