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Old 06-09-2011, 12:05 AM
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Rockester QuadraJet Tuning Tips

Hey guys I called up a local mechanic and found out they wnted 60$ to just tune my carb on my truck. Id rather learn how to tune the carb on my own than pay someone to do it for me. I was wondering if you guys have any tricks when tuning up a QJet. Ive read that they can be great carbs with some modification and dialing in componants. Im not quite ready to jump into a full rebuild/modification just yet but i was wondering if you guys could help me get it dialed in as well as it will get without pulling it apart.
Im sure its not just my carb but my truck just doesnt have that push you into ur seat feal and id like to try and improve on that by starting with my carb. It actually sounds like it boggs out when I really stomp on it. What could be the cause of this?
My trucks got a sbc 350 thats just about stock aside from a proformer 2101 intake manifold, K&N air cleaner, Headers... Could one of you Qjet guru's teach me the way of the Qjet
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Old 06-09-2011, 12:40 AM
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Before diving into the carb, dial in the ignition timing first. To set the timing, you'll need a timing light and to help w/the tuning of the engine including the carb, you'll need a vacuum gauge. Once the timing/timing curve has been dealt with, THEN you can start tuning the carb.

A stock distributor almost always needs to have lighter springs installed on the weights of the mechanical advance. Most all parts stores carry a kit that has the springs along w/weights that you won't need. Get the correct kit for either the HEI or points distributor depending on what you have.

Often an adjustable vacuum advance is needed or at least a limiter plate installed to limit the vacuum advance to around 12 of additional timing. You want to set the vacuum advance to be fully advanced at a vacuum about 2 in/Hg less than the idle vacuum when in Drive (neutral if using a manual trans).

The initial timing (w/o the vacuum advance hooked up) can start at about 10-12 BTDC w/the total of about 36 all in by no more than 3000 RPM. To get this, sometimes the distributor needs modified. Hook the vacuum advance back up after the initial and total timing has been set. You will want to try both a manifold and ported vacuum source to see which works better w/your combo.

You should verify that what you are seeing at the damper and timing tab for TDC is actually TDC.
DETERMINING TDC will allow you to be sure the timing tab and damper are correctly indicating TDC.

MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light. You can also buy a timing tape, they're not very expensive.

Be sure the mechanical advance plate is free to move, w/o binding or friction. HERE'S an exploded view of an HEI distributor. THIS is a description of an HEI rebuild.
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Old 06-09-2011, 07:54 AM
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Buy yourself a copy of this book before you do any work on the carb.

http://www.cliffshighperformance.com/buy_book_2.html
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Old 06-09-2011, 09:01 AM
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Quote:
Originally Posted by FmrStrtracer
Buy yourself a copy of this book before you do any work on the carb.

http://www.cliffshighperformance.com/buy_book_2.html
Cliff has his own forum on his site.
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Old 06-09-2011, 10:56 AM
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Quote:
Originally Posted by FmrStrtracer
Buy yourself a copy of this book before you do any work on the carb.

http://www.cliffshighperformance.com/buy_book_2.html
+1
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Old 06-09-2011, 11:52 AM
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Dang nice!!! I was actually gonna get that book today didnt know he had a website and forum though. Thanks guys
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Old 06-10-2011, 07:26 PM
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Cliffs carb mods for the performer cam sbc engine, on a QJet are dead on. Smooth and aggressive. My bet is the other recomendations are spot on.
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Old 06-12-2011, 11:25 PM
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Hey guys So I called up my uncle before I messed with my carb and timing...Had a long talk about all his chevy's and what my truck was having problems with. I told him I was going to mess with my timing and carb to try and stop my truck from running so lame. He told me to go get new fuel filters, spark Plugs, spark plug wires. After napa gave me the wrong ones, and charged me for 2 sets I decided to goto O'reilys and the guy over there hooked me up with the correct ones. Went back home and put all my new stuff on my truck and took it out for a test drive and......No more horrible stumbly bog noise!!! My truck can actually burn out now Im pretty dang happy right now. I think im still going to check and see what my timings at. And maybe mess with my carb a bit cause my idle seems high...My step dad decided he could set the timing by ear and I didnt want to be a dick to him and knock on how he set it up but its not all that great. Just figured id tell you guys the status.

I went to pull out of his driveway and my truck was idling so low it died. He messed with it some more and not the idle is pretty high in park and decent sounding in gear. I messed with the carb a little to get the idle in gear down a bit i think. Now my trucks idle is pretty dang high in park, drops down and sounds pretty nice in gear but Im gonna see if i can get to idle lower in park and about the same as it sounds in gear right now.

Last edited by GUITAR1989; 06-12-2011 at 11:30 PM.
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Old 06-13-2011, 06:57 AM
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Quote:
Originally Posted by GUITAR1989
Now my trucks idle is pretty dang high in park, drops down and sounds pretty nice in gear but Im gonna see if i can get to idle lower in park and about the same as it sounds in gear right now.
Sounds like low timing.

Make sure that the vacuum advance hose is connected at both ends and in good shape. If that's okeedokee, get a timing light on it and set the initial timing at 12 degrees. Don't forget to disconnect the vacuum hose to the distributor and plug it while you set the timing and reconnect it after. You'll probably have to dink with the idle speed a bit during and after this.
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Old 06-18-2011, 03:19 PM
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Man this thing is giving me a hard time . So I went to lower my idle and at a certain point the plate just wont even engage the screw when lowering idle. I tried to tighten up a spring that pulls down on the mechenasm and makes the plate move foreward twards the screw but when i give it gas the plate usually doesnt go back foreward and make contact with the screw. So the lowest i could get the idle is 900-1000....

Now for my timing troubles. I marked the tdc spot on my balancer with some white paint. I began to advance the timing..I saw it make its way onto the timing degree tab. I kept advancing it twards 10-12 but before i can even get it to 10-12 degrees my distributor wont turn any more. Could my top dead center mark be wrong on my balancer. Im pretty irritated right now please help me out...

also its clockwise to retard and counter clockwise to advance right? when i do get my distributor turned all the way counter clockwise my truck just dies.
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Old 06-18-2011, 04:47 PM
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So now i got the timing to 12 degrees before tdc and my trucks running hot. When i give it gas a fat puff of steam or gas "not sure" comes flying out of the top of my carb. what the hecks going on. My step dad messed with my carb and timing and got it all out of wack. this was my attempt to get the timing on wich it is at 12degrees but its running like ****...i really wouldnt even call it running. What should i do?
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Old 06-18-2011, 05:27 PM
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CCW advances a SBC. Be positive the wires are connected to the right plugs and are in the correct order on the cap!

1-8-4-3-6-5-7-2
The wires go into the cap CW. #5 and #7 are easy to mix up.

Set the timing with the vacuum advance DISCONNECTED and plug the hose going to the engine. Then see where that puts the total timing at. When you get the answer to that, get back to us. Reconnect the hose to the vac. advance when you are done.
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Old 06-18-2011, 09:20 PM
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Q-jet....issue...quick question

Is this a automatic vehicle or a stick? is it the original 350? if so what year we talking about here? R u running a Hei Distributor or points and condenser?

i'd be curious to know if its the original stock carb or an aftermarket?

What if any pollution controls...depending on the year would it could make a huge difference in setup and performance vs fuel mileage....how many miles on the motor? possibility of timing chain stretched out with a higher mileage vehicle will also cause timing idleing issues..Something to consider with out being able to be under the hood to know for sure.....

on older 350's I have also had great success with the edelbrock afb style carbs...there easy to setup.. might want to consider useing that style of carb. performance/mileage if thats what your hopeing to accomplish.

Just a thought.....

Last edited by OneSpeed; 06-18-2011 at 09:30 PM.
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Old 06-18-2011, 09:59 PM
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Thanks verry much man. Im not sure what year the engine is but the carbs a 1975 quadrajet not sure about polution controls, trannys a auto th375, im not sure on the engines mileage, GM HEI... I also pluged my vacuum gauge in and it was only reading 7-8 Im sure my engine needs alot of love to run good. Im just going to take it to a mechanic and have them tune the carb and timing. I had it on the freeway today and on a verry slight uphill slant it wouldnt even go over 55 mph.
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Old 06-18-2011, 10:28 PM
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my thought on the idle issue with not hitting the stop is 1 of 2 things 1)timing set to high. 2nd the low idle mixture screws could be askew(bent) or turned in to tightly(damageing the needle and seat) on pre adjustment....quick test for damage is to start the vehicle and 1 at a time turn the needle in (clockwise) keeping in mind the amount of turns it takes til stalls out or stops in the closed position (gently)...then just turn it back out til you return them to there original position... Noteing the whole time is running rougher or did it or didnt it stahl out?.......If by some chance u turn them all the way in and the motor continues to run...that means you have a vacuum leak somewhere....resulting in a non adjustble idle(higher idle speed)with the idle adjustment screw.....

Could be the culprit resulting in your low vacuum numbers at idle...
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