Carb question... please help me - The 1947 - Present Chevrolet & GMC Truck Message Board Network

big_c_snow · 12-24-2003, 01:06 AM

Hey all, I have a quick question.. how do you correctly tune a 1986 Quadrajet on a 305? I ask this because my truck is running very rich and has trouble with cold starts, and I wish to correct this before I sell it. So, the question is, how do I correctly tune that carb? Is there some sort of special tool I need, or can I do it with a normal screwdriver? How far out do I turn the screws? Thanks!

85 K5 · 12-24-2003, 09:54 AM

These carbs don't necessarily get out of tune, they get dirty. If you are willing get the Doug Roe book on Qjets and a rebuild kit. Take your time and all will go well, it's not that hard.

Grim Reaper · 12-24-2003, 12:58 PM

Uggg 86 is heavy emmisions.

86 uses electric choke AND a mixture solonoid. The mix solonoid adjust by using a thermostat in the intake. It vaires the gound and that changes the speed it osilates and the fuel mixture.

First thing to do is make sure your getting power to the choke once the engine is started. No power then this is a electrical problem before the carb. Check fuse and check that everything is plugged in. The wire from the choke will go to a oilpressure switch that is either behind the distriubutor or above the oil filter. This is to prevent the choke from cycling if the engine is not running.

If you have power at the choke follow the wire over to the top of the carb where it plugs into the mixtures solonoid. The second wire coming out of that will go to the thermostat on the intake. If you have a meter that will measure amps see what that groundwire has on it. No meter take a test light hooked to ground. Probe the wire while everything is plugged up. If the light comes on then the thermostat is probably good.
Unplug the wire from the thermostat and probe the wire going to the solonoid. If the light comes on the solonoid is probably good.

Next wouldbe to check choke function. Fire it up cold and watch the choke and make sure it opens fully after about 5 minutes if it's about 32f outside.

Let us know what you find.

**old Rusty C10** · 12-24-2003, 01:15 PM

its not so easy to rebuild the kits cost $50 andive tried once and gave it to someone else to go over they were a real mechanic
unfortunately new rebuilts go for $$$ id say look for a junkyard one in good shape

**swervin ervin** · 12-24-2003, 01:53 PM

There was no idle mixture solenoids in any of our trucks. Only thing they had different than other Q-jets was the dual capacity accelerator pump system. A 86 Q-jet was no different than a 85. The tuning is done the same way you would do it on any other year. But, it must be up to operating temp so the pump will be single capacity and not dual. One thing to check is make sure the wire to the sensor at the thermostat housing is hooked up. This is what controls the dual capacity pump solenoid.

I agree on a rebuild. Q-jets don't go out of tune, unless someone has messed with them before and got it all out of wack. 99% of the time when a Q-jet is running rich, for no apparent reason, it's just dirty and needs a good cleaning and rebuild. The float needle wears out and won't shut the fuel off properly.

Rebuild kits are not expensive. Advance sells them for around 25 bucks. But, use regular carb dip to clean them. The spray stuff or gas won't do the job.

Rebuilding a Q-jet is a snap. Everyone thinks they are hard, but they're really easy. Another thing to check for is worn throttle shafts. If this is the case, which happens a lot on these trucks, it will need to be rebushed.

79Chevypickup · 12-24-2003, 01:57 PM

This site might help....

http://www.carcraft.com/howto/57178/

adjust the mixture screws 2 1/2 turns then start her up,allow to warm up and lower idle speed to 650rpm out of gear,turn one mixture screw in until the engine stumbles then slowly turn the screw out until you have the highest smoothest rpm,repeat the procedure with the other screw,then fine tune by going in or out with both screws until she is steady and smooth,chock the front wheels,set the emergency brake then place her in gear then from THE SIDE OF THE VEHICLE NOT FROM THE FRONT adjust the screws until the idle is very smooth,then adjust idle speed to 650rpm in drive and that is all.shur her off and install the airfilter then test drive

big_c_snow · 12-28-2003, 03:20 AM

Ok, new problem.... my truck now doesnt like to go over about 45 unless I floor it. And it wint drive around right at simple cruising speed... I hope it's the carb that needs tuned, cuz thats an easy fix. Otherwise..... anyone wanna buy a truck? I need the types of fixes that I can do for free, it's either that or I could probably trade a Bronco 2 for a 327 thats in a cousin's yard that hasnt run in 2 years, but is known to run well. Anyways, please help me, because I think htat this is the root cause of my bad gas mileage. Thanks!

RodKnockin · 01-04-2004, 01:52 AM

Well I went though the same exact thing with my 86 , and I'm here to tell ya the problem your having can only be fixed by rebuilding it. I have a friend that has been rebuilding only carbs for 15 years, and he's built them all. he tried to adjust it, but no luck. coulb be something simple. but I doubt it. he told me that a Quad needs a new float every 5 years weather you think it needs it or not. He said they get saturated with fuel, don't work right. they allow extra gas to get dumped in the carb (sometimes). he rebuilt it for me and it works great.

Quads are the best carbs ever madefor daily driving, there the most efficient ones out there.

12-24-2003, 01:06 AM	#1
big_c_snow Registered User Join Date: Feb 2003 Location: Tampa, FL Posts: 157	Carb question... please help me Hey all, I have a quick question.. how do you correctly tune a 1986 Quadrajet on a 305? I ask this because my truck is running very rich and has trouble with cold starts, and I wish to correct this before I sell it. So, the question is, how do I correctly tune that carb? Is there some sort of special tool I need, or can I do it with a normal screwdriver? How far out do I turn the screws? Thanks! __________________ 94 Ford Aerostar AWD Which is useless in Florida... 86 FJ1200 Daily Driver

12-24-2003, 09:54 AM	#2
85 K5 Registered User Join Date: Nov 2002 Location: Spring TX Posts: 113	These carbs don't necessarily get out of tune, they get dirty. If you are willing get the Doug Roe book on Qjets and a rebuild kit. Take your time and all will go well, it's not that hard. __________________ 350 Crate 10 bolt 3.73 2.5 lift 32x11.50 1904 Edelbrock http://www.oplnk.net/~spirit/K5front.jpg

12-24-2003, 12:58 PM	#3
Grim Reaper Registered User Join Date: Jul 2001 Location: Atlanta GA Posts: 1,704	Uggg 86 is heavy emmisions. 86 uses electric choke AND a mixture solonoid. The mix solonoid adjust by using a thermostat in the intake. It vaires the gound and that changes the speed it osilates and the fuel mixture. First thing to do is make sure your getting power to the choke once the engine is started. No power then this is a electrical problem before the carb. Check fuse and check that everything is plugged in. The wire from the choke will go to a oilpressure switch that is either behind the distriubutor or above the oil filter. This is to prevent the choke from cycling if the engine is not running. If you have power at the choke follow the wire over to the top of the carb where it plugs into the mixtures solonoid. The second wire coming out of that will go to the thermostat on the intake. If you have a meter that will measure amps see what that groundwire has on it. No meter take a test light hooked to ground. Probe the wire while everything is plugged up. If the light comes on then the thermostat is probably good. Unplug the wire from the thermostat and probe the wire going to the solonoid. If the light comes on the solonoid is probably good. Next wouldbe to check choke function. Fire it up cold and watch the choke and make sure it opens fully after about 5 minutes if it's about 32f outside. Let us know what you find. __________________ Grim-Reaper 70 Pontiac LeMans Sport Convertible, worlds longest resto in progress Looking for 71-72 2wd Blazer or Jimmy Project

12-24-2003, 01:15 PM	#4
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,313	its not so easy to rebuild the kits cost $50 andive tried once and gave it to someone else to go over they were a real mechanic unfortunately new rebuilts go for $$$ id say look for a junkyard one in good shape __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

12-24-2003, 01:53 PM	#5
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	There was no idle mixture solenoids in any of our trucks. Only thing they had different than other Q-jets was the dual capacity accelerator pump system. A 86 Q-jet was no different than a 85. The tuning is done the same way you would do it on any other year. But, it must be up to operating temp so the pump will be single capacity and not dual. One thing to check is make sure the wire to the sensor at the thermostat housing is hooked up. This is what controls the dual capacity pump solenoid. I agree on a rebuild. Q-jets don't go out of tune, unless someone has messed with them before and got it all out of wack. 99% of the time when a Q-jet is running rich, for no apparent reason, it's just dirty and needs a good cleaning and rebuild. The float needle wears out and won't shut the fuel off properly. Rebuild kits are not expensive. Advance sells them for around 25 bucks. But, use regular carb dip to clean them. The spray stuff or gas won't do the job. Rebuilding a Q-jet is a snap. Everyone thinks they are hard, but they're really easy. Another thing to check for is worn throttle shafts. If this is the case, which happens a lot on these trucks, it will need to be rebushed. __________________ Mike 1985 Chevy C-10

12-24-2003, 01:57 PM	#6
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	This site might help.... http://www.carcraft.com/howto/57178/ adjust the mixture screws 2 1/2 turns then start her up,allow to warm up and lower idle speed to 650rpm out of gear,turn one mixture screw in until the engine stumbles then slowly turn the screw out until you have the highest smoothest rpm,repeat the procedure with the other screw,then fine tune by going in or out with both screws until she is steady and smooth,chock the front wheels,set the emergency brake then place her in gear then from THE SIDE OF THE VEHICLE NOT FROM THE FRONT adjust the screws until the idle is very smooth,then adjust idle speed to 650rpm in drive and that is all.shur her off and install the airfilter then test drive __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

12-28-2003, 03:20 AM	#7
big_c_snow Registered User Join Date: Feb 2003 Location: Tampa, FL Posts: 157	Ok, new problem.... my truck now doesnt like to go over about 45 unless I floor it. And it wint drive around right at simple cruising speed... I hope it's the carb that needs tuned, cuz thats an easy fix. Otherwise..... anyone wanna buy a truck? I need the types of fixes that I can do for free, it's either that or I could probably trade a Bronco 2 for a 327 thats in a cousin's yard that hasnt run in 2 years, but is known to run well. Anyways, please help me, because I think htat this is the root cause of my bad gas mileage. Thanks! __________________ 94 Ford Aerostar AWD Which is useless in Florida... 86 FJ1200 Daily Driver

01-04-2004, 01:52 AM	#8
RodKnockin Registered User Join Date: Dec 2003 Location: East Tennessee Posts: 14	Well I went though the same exact thing with my 86 , and I'm here to tell ya the problem your having can only be fixed by rebuilding it. I have a friend that has been rebuilding only carbs for 15 years, and he's built them all. he tried to adjust it, but no luck. coulb be something simple. but I doubt it. he told me that a Quad needs a new float every 5 years weather you think it needs it or not. He said they get saturated with fuel, don't work right. they allow extra gas to get dumped in the carb (sometimes). he rebuilt it for me and it works great. Quads are the best carbs ever madefor daily driving, there the most efficient ones out there.



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