Carb tuning questions
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Tuned
Joined: Nov 2009
Posts: 407
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From: Rochester
Carb tuning questions
I've got an 86 f150 300 offy dual port with a quadrajet carb and efi manifolds. I've got the truck running good idles good. When I take off it takes off good and crisp throttle response. But when u floor it it bogs for a few seconds and then takes off. Is this a to rich mixture? I've noticed running through the gears that it has a few flat spots. But when I hit 3rd it bogs alittle. If I'm crusing in 3rd at like 35 or 40 and get on it it bogs and wot do anything unless I let off and ease into the gas. Acts like it's trying to open the secondaries but doesn't. It runs fine and drives great until I get on it runs through first and second and then kinda shutters in third then goes. It's got a 4 speed in it so I know 3rd and 4th aren't power gears. Any ideas on what I could try? Thank for any help!
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Tuned
Joined: Nov 2009
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From: Rochester
This is probably a stupid question to ask but how to u tighten the secondaries? I looked and didn't see how to. Not to familiar with this carb so it's a learn as I go! Thanks for all the help though!
Postmaster
Joined: Dec 2006
Posts: 3,603
Likes: 10
From: Spokane, WA
IIRC there is a spring on the secondary air flap that can adjust the spring tension.
My Quadrajet Tips Scroll down to the air valve adjustment.
QuadraJet secondary adjustment - Google Search
"You can then adjust your idle speed. If the carb had developed a "hesitation" when opening the secondarys, you need to adjust the secondary air flap (the flap that you can push open from the top). You want to do this with the engine OFF. Get a small blade, straight screwdriver and locate the adjustment screw (passengers side near the air flap) and the allen bolt set screw (below adjustment screw). Usually I "mark" the current location on the carb casing as a baseline. Insert the screwdriver first to hold the current setting, then loosen the allen screw (there will be tension on the screw so don't let go without tightening set screw). Usually if the carb has a "hesitation" it is because of the air flap opening too quick. Adjust the screw to "tighten" the tension on the air flap. This is very delicate spring inside the adjustment screw, so take it easy - only about a 1/4 turn per "Test". Tighten the allen screw then start engine and "Test" the secondary action (Mash the petal to the metal). If the "hesitation" is still there, keep adjusting till it goes away."
That is from here: http://forums.off-road.com/gm-standa...ning-qjet.html
My Quadrajet Tips Scroll down to the air valve adjustment.
QuadraJet secondary adjustment - Google Search
"You can then adjust your idle speed. If the carb had developed a "hesitation" when opening the secondarys, you need to adjust the secondary air flap (the flap that you can push open from the top). You want to do this with the engine OFF. Get a small blade, straight screwdriver and locate the adjustment screw (passengers side near the air flap) and the allen bolt set screw (below adjustment screw). Usually I "mark" the current location on the carb casing as a baseline. Insert the screwdriver first to hold the current setting, then loosen the allen screw (there will be tension on the screw so don't let go without tightening set screw). Usually if the carb has a "hesitation" it is because of the air flap opening too quick. Adjust the screw to "tighten" the tension on the air flap. This is very delicate spring inside the adjustment screw, so take it easy - only about a 1/4 turn per "Test". Tighten the allen screw then start engine and "Test" the secondary action (Mash the petal to the metal). If the "hesitation" is still there, keep adjusting till it goes away."
That is from here: http://forums.off-road.com/gm-standa...ning-qjet.html
Junior User
Joined: Mar 2003
Posts: 74
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From: On the Alabama River
Here's some more:
All the QuadraJet Information I have found on the Internet
There's a manual in there from '73 good reading.
I've messed with them before so I'm somewhat familiar with them. But no expert by any measure. Looks like I may have thrown a few good ones away when I was younger cause I didn't understand the dynamics.
All the QuadraJet Information I have found on the Internet
There's a manual in there from '73 good reading.
I've messed with them before so I'm somewhat familiar with them. But no expert by any measure. Looks like I may have thrown a few good ones away when I was younger cause I didn't understand the dynamics.
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Tuned
Joined: Nov 2009
Posts: 407
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From: Rochester
WOW That made a world of difference. Works better when it actually has some tension on it. It wasn't even tight just flapping there!! I've got one more question. I've got two tiny vaccum leaks around the front two intake runners. Found this by spraying carb anc choke cleaner around there. Any way of fixing this without having to pull the whole thing off and start over? I've tightened the bolts up but didn't work still leaks. A friend told me to put forma gasket around them and that it would be ok? Would it hurt anything to do that or am I better off getting another gasket and doing it over? Thanks for all the help!!
Postmaster
Joined: Dec 2006
Posts: 3,603
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From: Spokane, WA
Some good reading in the files for sure. Some of the links further down the page are dead though.
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Freshman User
Joined: Jan 2007
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Harte3's right about the secondaries. Sounds like they're too loose. Even on a Dodge 360 I had to tighten them. The pump shot is helps transition also but if you adjust it so that there's no stumbling when only on the two barrels, it should suffice for the transition to 4 barrel.
Adjust the 4's tension and if you get where it's too tight, you may have to change secondary rods- real easy- and then readjust 4's spring.
Might get a fuel regulator. Quads seem to like 3psi or so.
Adjust the 4's tension and if you get where it's too tight, you may have to change secondary rods- real easy- and then readjust 4's spring.
Might get a fuel regulator. Quads seem to like 3psi or so.
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Postmaster
Joined: Dec 2006
Posts: 3,603
Likes: 10
From: Spokane, WA
As regards the vac. good luck trying to stop it from the outside...usually just doesn't work.
Got the bog out of the Quad-bog, eh? Good job!
Carb tinkering can be fun when the tinkering works.
Got the bog out of the Quad-bog, eh? Good job!
Carb tinkering can be fun when the tinkering works.
Freshman User
Joined: Jan 2007
Posts: 36
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Harte3
What are you talking about? You can talk all your crap about heads 'cause I don't have alot of practical experience;but' I will not try to console you about quads.
Don't ever respond to another question I pose.
Don't ever respond to another question I pose.
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