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The best way to tune a Q-jet is to take it off, and screw on a Holley...
(OK, so it wasn't much of a joke...)

There aren't any really easy ways to tune a Q-jet I know of...
It's all modify, test, modify again, test again, ECT. ECT. ECT....

Use a vacuum gauge to set the idle mixture just like every other carb, but after that, you are pretty much at the mercy of new needles, 'jets'
and a very precision drill set.

I'm not much of a Q-jet fan. I don't like anything about them.
I'm told they do off camber better than a Holley, but a Holley has it all over them in every other respect...

Sorry I couldn't help.
Aaron.


"I Have The Body Of A God... Buddha"
 

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Same as any other carb...
VERY LIGHTLY bottom out the idle mixture screws, then back them off 1-1/2 turns.
Hook a vacuum gauge to manifold vacuum (not the PCV line).
Adjust the screws until you get the highest vacuum reading.

The screws MUST turn together. Both in or both out together.
I normally do 1/4 turn at a time, and when you get close, blip the throttle in between adjustments.

Be very careful to take it easy on the adjustment needles. They are fragile.

The screws must be turned out the same amount unless you have an exhaust gas analyser and completely separated dual exhaust.
Those little rich/lean indicators are nice for this if you have headers with O2 sensor nuts already welded in.
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CLOSELY check the accelerator pump on any Q-jet.
They used the dumbest possible method to incorporate an accelerator pump, so of course it fails on a regular basis.
Usually leaking fuel out when compressed, and air back into the chamber when you let up on the pump...

This leakage of fuel out is a fire hazard.
The air leakage into the chamber means air is taking up space fuel should.
Air compresses.
So when you hit the throttle, the air compresses, and makes the pump shot late.
With the air taking up room that fuel should, the pump shot is short, weak, and full of bubbles.
More of your shot is leaking out of the chamber past the seal, furthering starving the pump shot...

Stupid and unsafe design.

Causes huge off the line stumble.
That's the 'Q-Jet Cutout'... Stomp on it, and it seems to fall on it's face before it takes off...
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Everything else is metering rods, bending linkage, lightning weights and drilling holes, all too complicated to describe without pictures.
It's more of an art than a science when you are working with carbs anyway...
Carter AFB's are the worst, then comes Q-Jets, after than comes the knock-offs, like Edelbrock and Webber....
Holley is the most tuneable, but with all the adjustments, it's easy for beginners to go the wrong way...
Inglese (what Webber copied from) is probably the second most tuneable, but it has the same problem with beginners that Holley does.
Predator is probably the most end user friendly carb on the market that actually works as advertised. It only has three adjustments...

Holley just kicked Barry Grant's ass again with the release of the new super tuneable line...
They really are something, but I'm sure with 12 to 15 new adjustments on them, even more people will be playing with things they don't understand....
I just wish Holley would do the Grant thing and make interchangeable venturis for the main body, and I wish they had Annular discharge nozzles on all performance carbs...

I'm rattling on again....
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Good luck, and happy hunting!
Aaron.

"I Have The Body Of A God... Buddha"
 

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My assessment was that I had been told that Q-Jet did well on off camber situations.
Did you miss that?

Holley will kick any Q-Jet in the butt on everything else. I can get a Holley to do just fine up to about 35 degrees, but it sure won't do it out of the box like a Q-Jet will.

Everything else about a Q-Jet, from the lousy integral filter to the ill designed linkage, is crap.
What were they thinking when they stole bad designs from stromburg and carter to build that piece of crap...?...
(That makes carter an even bigger piece of crap...)

Vic Edelbrock fixed a lot of problems on the AFB, and called the redesign a "Performer"...
Good joke there!!
Just because it doesn't leak all the time, and the secondary throttle bores are actually of some use doesn't mean it works...

Holley is still the hottest ticket out there, and the most tuneable.
They just don't take a twist very well with out doing some tune up work first...

I've been playing with a new Holley with all the tuning extras they just built in, and one of the new Barry Grant Demon carbs...
Holley kicks Grant a$$ again!!
I just wish Holley would do the interchangeable venturi bores like Grant does...
That is the ONLY thing the new Holley is missing to make it perfectly tuneable...

Re-read the first post, I didn't undercut Q-jet's ability to do off camber...

"I Have The Body Of A God... Buddha"
 

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To make a Holley go off road at the RPM's you described, it takes a change from those huge floats in the dual line, center hung float bowls that everyone is so fond of....
They just can't give up that chrome fuel line!!

When you go to the smaller side pivot float bowls, with the more or less round floats, and the off road needle and seats, lower the fuel level about 1/16", and lower the fuel pressure to about 4 or 4.5 Lbs, they will do pretty good...
I also use short jet extensions on both ends, and vent tube extensions out the top...

Most guys that go off road listen to the so called 'Speed Shop' jokers, and wind up with a power valve that opens just as soon as they lug it down low... Bad situation...
Jeep already in a bind, and suddenly 30 to 40% of the total fuel that carb can flow is dumped into the intake....

Off roaders need at least two In.Hg difference, and a lot of them need up to five In.Hg difference.
The speed shop will put them as close as one half inch away, and then it's flood time...

I always could make a Q-Jet run OK, but nothing like a Holley...
Q-Jets take constant maintenance also, if you are going to keep them working correctly, and not having them leak...
I don't think I've ever seen a Q-Jet that was six months old that wasn't fuel stained from leaks, no matter who built it.
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I'm going to say it again, just for the record...
I am told Q-Jet's do really well for off camber situations.
I have seen several of them in off road situations that would scare me.

Most people in the know agree, if you can't afford fuel injection, use a Q-Jet.
I don't turn my jeep upside down (unless drunk), so I don't have much call for something that will run on it's side...

I have been intrigued with the pictures of the rock crawling guys though.... /wwwthreads_images/icons/wink.gif
(maybe next year...)

See you all, Aaron.

"I Have The Body Of A God... Buddha"
 

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We put together a basic speed/ density fuel injection system in the early 80's that was all stock parts, except for the little twist knob no one gives you on any stock system.
We used it to go 7.5 rich one way, 7.5 lean the other way...
How we tuned it over the mountains was to punch the throttle, and ask the guy behind us to rate the black smoke cloud on a scale of 1 to 10...
I'm so glad I didn't know all the things that could have gone wrong with that system then!!
It worked pretty well, so we tried to market it... Not much luck making any money during a depression, but we had a lot of fun, and learned a lot...

I think if I do a rock crawler later on, I'm just automatically going to use fuel injection and a dry sump oil system.
With a fuel bladder, I should be able to run up-side-down.... /wwwthreads_images/icons/wink.gif

Later folks, past my bed time...
Aaron.

"I Have The Body Of A God... Buddha"
 
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