strange carb issues

[msc66]

I've had 2 different pro built Q-jets on my car and with both I get really low vacuum readings (fluctuates between 5 and 8 inches) and a really rough idle. Both builders are reputable. Dean Oliver and John Osborne. And both ran the carbs on their cars before shipping.

Odd thing is I borrowed a 650 holley and when I put it on the idle smoothed out and the vacuum jumped to 11 -12 inches (respectable for my cam). This would seem to indicate the q-jets as the problem but I find it hard to believe that I got 2 bad carbs from 2 different reputable builders.

I've done all the vacuum leak checks and I'm trying to find someone that will let me try one of the q-jets on their car but if any of you guys have any suggestions please chime in.

[70.5CAMARO]

Re: strange carb issues

were are you located at?

[TheSilverBuick]

Re: strange carb issues

First thing that comes to my mind is that the Q-jet is a vacuum metered (load sensing) carb and the Holley just uses air velocity and jets. Meaning the Q-jet may be trying to richen up the mixture from a fluxuating idle, hence killing the vacuum at the same time, the holley may just be simpler to lean out and less sensitive to vacuum changes. I've never had a car or worked on one with a lopey idle or low vacuum to trouble shoot idle issues though, so it's kind of a guess.

[TC]

Re: strange carb issues

What is your timing at idle set at.

[milner351]

Re: strange carb issues

was the holley square bore and the q-jet a spreadbore?

so you had to use an adaptor to install the holley?

is there then something wrong with the mounting surface of the spreadbore intake perhaps?

Seems wierd - that's a head scratcher.

[msc66]

Re: strange carb issues

were are you located at?

Atlanta, GA

[msc66]

Re: strange carb issues

The holley is a square bore and the q-jet a spread bore. The intake is a spread bore but its drilled for both. Your supposed to be able to just bolt either carb on but I did use an adapter plate for the holley just to be safe.

I checked the mating surface and it appears flat. I tried doubling the gaskets as well.

The timing is at 22* initial which is what others with this or similar cams are running.

Silverbuick,

I'm following what you're saying but the guys that build these q-jets require every last detail about your cars build including cam specs. I've talked to a lot of guys on the buick and pontiac boards that have used these guys and also Cliff Ruggles for their q-jets and have had no problems so I don't know?

I ordered some intake gaskets so next I'll pull the intake to see if I have a leak from the valley into the intake ports. ???

[TC]

Re: strange carb issues

You can check for vacuum leaks with a vacuum gauge, if the needle jumps around you most likely have one.

[milner351]

Re: strange carb issues

if you have a leaking intake gasket, shouldn't it show up with both carbs?

[Loren]

Re: strange carb issues

Q-jets are full of spooks. Books won't tell you, but some know the truth...It may not be possible to make a Q-jet work without having something from the netherworld working alongside.

I know two people who are self-described experts, who swear by those things and tinker away with them...neither person seems capable of building one that works on anyone else's car. I have a 454 truck with one that has been gone through 3 times by 2 different shops and still doesn't work. For a boat I ran through THREE individual NAPA-rebuilt Q-jets and not one would even START. Finally I threw on a used Holley from a bud and it worked perfect. My old Q-jet truck is the reason my next truck was TBI. Seriously, I was SICK of messing with it. So you can tell me that all it takes to make a Q-jet work is someone that knows what they're doing...yes, I've heard it again and again. Yet I've never met or known of one of those individuals or shops. ???

One time I bought a rebuilt from Kragan and it worked well. Lucky shot, it never happened again.

Those folks who know and can succesfully fix a Q-jet surely walk among us, but they are very likely evil. Witches. Tech manuals and Oija boards, worshipers of the anti-Christ. Watch out for them. You may get a good carburetor, but you will pay with your soul.

So just get a Holley or switch to F.I., my advice. ;)

[Caddyman]

Re: strange carb issues

Worn baseplate and throttle shaft. Probably on the drivers side of the engine (its loaded more with both the return spring, TV cable, and throttle cable).

They are building it "square", you're installing it "warped" (maybe intake or adapter sorta pulling the plate unevenly?)...and its allowing the shafts to leak air.......

Common with a Q-jets with more than, ? 50K miles?....


Spidey will understand....they all leak....its a matter of how much...........

Some are so bad AFTER you remove them for repair or to remove mixture screws, you can't REUSE them!
Q-jet baseplate problems are so common, most dealers used to STOCK plates in the late '80s.

[msc66]

Re: strange carb issues

Throttle shaft bushings were replaced with the rebuild. I've heard of the warped airhorns from over tightening but not baseplates. Still, wouldn't a double gasket seal it up? If it was warped that bad wouldn't you be able to see it with a straight edge on it?

[min301]

Re: strange carb issues

I've had alot of time with em, had good luck with em...


Those folks who know and can succesfully fix a Q-jet surely walk among us, but they are very likely evil. Witches. Tech manuals and Oija boards, worshipers of the anti-Christ. Watch out for them. You may get a good carburetor, but you will pay with your soul.

...I'm none of the above. 8)

[dhondagod]

Re: strange carb issues

Spray a little carb cleaner over the air-horn when its running and see if it smoothes out/idles up. This will tell you if its lean or not. If it stumbles and drops RPM then its rich.

For whats its worth getting a carb to run correct isnt black magic but simply understanding exactly whats going on inside one and being able to make neccesary changes.

That being said, I preferr EFI because its even easier than carbs.

Chris 8)