Carb issues, just chime in.
 

chevy 454 with edlebrock q-jet intake. Decent size cam in it.

So, i tried to run a quadrajet that i had. Can not get it to idle. the guy working on the car has years and years on these things. there is some corrosiion building up in it and thinks that some of the fuel passages may be getting clogged. The vehicle just can not maintain a normal idle. It will idle fine, then not, then normal again.

Tore it all apart. Everything looks good and we blew everything out.
im going to get a new carb. this one is 30 years old.

I was going to get a Edlebrock 1813 or 1413. Then i read that edlebrocks are awful and go with holley. Im lost. Any suggestions????

Re: Carb issues, just chime in.
 

Get the book by Cliff Ruggles and rebuild & re-tune the Q-jet. Seriously. All of my Q-jets are at least 30 years old, they've been rebuilt, and they run great. I wouldn't go back with an Edelbrock if I was paid to.

Re: Carb issues, just chime in.
 

Its been rebuilt, retuned twice already. By people who have experience with these things. Is edlebrock that bad??? I see them on everything.

Re: Carb issues, just chime in.
 

What are the cam specs? How much vacuum is the engine pulling at idle?

Re: Carb issues, just chime in.
 

Cam specs
Gross valve lift intake= .552 exhaust .555

Duration at .050 230 intake 236 exhaust.

Vacuum is within specs

Re: Carb issues, just chime in.
 

I have run a few Edelbrocks and have been happy with them, easy to tune and decent performance but...

I have pretty well settled to using Q-jets on everything because they really are a good carb when built and tuned properly. There are a number of online references that can help with the tuning process. My key question is whether the q-jet you are using is made for a big-block or not. Every q-jet that left the factory was specific to the motor it left with and that is usually the best place to start tuning for performance increases from. It is much more difficult to tune a carb for a 307 to a built big-block than one for a big-block.

Re: Carb issues, just chime in.
 

The carb is off the same engine. 81 454. But now i have a different intake manifold and cam.
Im running 12-14 ish degrees of timing at idle. The guy working on them has done so since he was a kid. He is pretty good with them, this one is just stumping him. I REALLY wanted to use this quadrajet also.

Re: Carb issues, just chime in.
 

Some more info.

There are no vacuum leaks internally or externally. Timing is right. The carb has been gone through and cleaned thoroughly. You can see were there is corrosion on the inside and my guy thinks that some of the fuel passages may have that corosion in there causing this weird idle.

Basically say it idles normal at 900rmp.. You then put it in drive and it just idles rough and lumpy, and when you put it back in to park, the idle stays ****ty.. You blip the throttle and it seems to be ok then back to idling ****ty.


Also, when you adjust the two front idle mixture screws. When adjusting those normally you will turn them in all the way, the vehicle will run rough, and you will start to adjust them out incrimently until the idle smooths, then you get to a point as you are adjusting them out that the engine starts to idle rough again. Then you know to adjust them back in on the smooth point. Well, on this setup that isnt happening. As you adjust them in all the way it runs crappy and as you start to adjust them out, the idle gets a tiny bit better but never changes. ALLLLL the way out and it doesnt do anything. Its supposed to go ****ty, smooth, ****ty again. DOESNT happen..

The one adjustment that sits under that plug on the top of the carb is still in a factory setting, that has not been changed yet. He didnt want to touch that because we didnt have any specs on where to even start.... Any thoughts/?

Re: Carb issues, just chime in.
 

Where do you have your vacuum advance hooked to on the carb? What you describe sounds like you have it hooked to full-time vacuum.

The adjustment under the plug on top of the carb has nothing to do with idle. It allows you to fine tune the mixture at cruise. Its called Adjustable Part Throttle, or APT.

As for the idle, you usually start with the screws turned out 2-4 turns out from fully in. Then turn them each out about 1/4 turn at a time until the highest idle rpm can be obtained. Then turn them in slowly until the engine speed drops 20-30 rpm and the reset the idle speed.

If you can't do that, it means your engine need so much air at idle that the throttle plates are too far open. There are ways around this, such as drilling small holes in the throttle blades, or making sure the idle bypass air circuit in the carb is open. Not all Q-jets used bypass air, and most that didn't will have most of the system intact. The Q-jet books explain this a lot better than I can.

Re: Carb issues, just chime in.
 

I'm not a Q-jet expert but I can do research. Your lift sounds a little lumpy so I looked around and found this. I hope it helps you!

http://www.73-87.com/7387garage/drivetrain/qjetidle.htm

Re: Carb issues, just chime in.
 

That sounds like it would work. I was also going to suggest checking the return spring tension on the throttle and making sure the idle is being set and consistently at the stop.

Re: Carb issues, just chime in.
 

With that much duration, your not going to get a low RPM smooth idle. I assume that the statment of "Vacuum is within specs" equals that you don't know. You have a big cam, get used to it, Its not going to idle like a stocker no matter what any of the guessers say.

Re: Carb issues, just chime in.
 

Thanks for taking the time. I read about all that. Everyone has their choices on carbs. The only thing that was consistent between everyone is that i would have more power with an edlebrock/holley on the low end then i would with a quadrajet. At the top end they should end up fairly equal.

I pulled the trigger and bought a 1814 edlebrock. Read all the instructions, installed the carb, fired right up, warmed it up, adjusted the idle, messed with the two mixture screws and it idles PERRRFECT, in drive and in park. I take it outside, and it is a completely different truck. I always thought a slightly built 454 would be kinda quick. Never felt that way. Well, today omg. I cant really even put into words how happy i am with how it runs. Its more then i expected.

Now i have this really clean fully functioning quadrajet that i dont know what to do with. i was debating making those changes that i have read and then reinstalling it and seeing if i can get it running right.

I read that. I might try that later if i get bored and want to get this quad running.

No, you are correct. As i was standing near the truck and he was checking vacuum i asked if its good, and he said ya. ahaha. 14-18 at idle??? I can check for you.

As for the idle. I dont want a smooth idle, thats not what im after. I was after an idle period. I put the new carb on and it idles and it idles freaking great.

Ya, that wasnt the issue, tried that. I will eventually mess with it until i can get it idling right. Glad i finally have a driveable truck.

Re: Carb issues, just chime in.
 

"Its been rebuilt, retuned twice already. By people who have experience with these things. Is edlebrock that bad??? I see them on everything."

Well I guess even some experienced folks have trouble time from time. Glad it works for you now! I've rebuilt a few and it's been more hit than miss. I have had to go back in, an redo again what I did before, because I'm still learning about the Quads'. Glad it's running fine. Now you can play with the Quadrajet knowing you have a solid back-up.

Re: Carb issues, just chime in.
 

I have no plans getting rid of the quad. I do want to try some of those tips to get this idling correctly. The edlebrock is on point. Thottle response is still immediate but there is just SOOO much more go right off the bat.

Re: Carb issues, just chime in.
 

If you are really interested in seeing if you can get that q-jet fine tuned, I strongly recommend Cliff's book as well.

I knew next to nothing about q-jet's (or any other carbs, for that matter), and this book lays it all out. Tore mine completely apart, and rebuilt with one of his kits (also had the primary throttle shaft rebushed....made all the difference in the world. I got it right the first time because of that book!

Re: Carb issues, just chime in.
 

On order...

Re: Carb issues, just chime in.
 

Bringing this back. Have some questions.

Driven the truck about 3-4 times. Idles good, starts good. Accelerates OK. It feels like it spits a bit under hard acceleration. Very hard to explain.

So i want to get it tuned. I would like to do it myself. I understand basic engine concepts. Timing, vacuum, and all that.. But i have never really messed with the acceleration portion of it. Or different jet sizes.

Without having wide band o2 sensor on the truck, how do you tell if you are rich or lean during accleration. Right now the truck goes pretty dang good, but if your doing like 30 and romp on it, it goes but you can tell its just not right. Very hard to explain what its doing. Almost feels like its missing a tiny bit under hard acceleration.

Re: Carb issues, just chime in.
 

I'd leave the carb alone. Concentrate on the timing now.
What's your initial timing?
Vacuum advance hooked up where?
Do you have a Timing tape or dial back to zero timing light?

Re: Carb issues, just chime in.
 

I will check my timing again.

I have both timing lights. Just the standard blink light and an expensive dial electric one.

Vacuum is hooked up to... let me get a picture.

http://img.photobucket.com/albums/v6...erson/edle.jpg

Its hooked up to manifold vacuum port.

timing is 14 at idle. then 32 ish at 3000 rpms. Thats what the timing was with the OLD carb. i put the new carb on and didnt readjust the timing. Didnt think that was necessary.

One side note. I have this SMALL ass air filter. When i take that off, the truck runs COMPLETELY different. Is that normal with an air filter??? The air filter is like 5 inches round, if that. Runs better without the air filter but still not right.

http://static.speedwaymotors.com/RS/...92511900_L.jpg

Let me know what to do next.

Re: Carb issues, just chime in.
 

Could be air cleaner related. Starving for air with a small filter. Try a test run with it on and off and see what that does.
One more thought. I've never had success tuning a motor in the winter.
And your timing curve. Quick or slow from idle to 3000rpm's.

Re: Carb issues, just chime in.
 

SOrry geez, i dont know what that means... When i rev and hold at 3000 it reads 32 ish...

With the air cleaner off, it does run better. Just doesnt seem right. As for winter tune.. When it was warmer on when i installed the carb, it ran alot better but would still cut out on power. It felt lean...

When i get home, im going to take off air filter. Check timing/idle. Drive it till its warm, then get on it and report back.

Re: Carb issues, just chime in.
 

The vacuum advance line should be hooked to the timed vacuum port. The manifold vacuum port will pull vacuum all the time, so you are advancing your timing slightly even at idle.

Re: Carb issues, just chime in.
 

Man, i have researched this topic OVER and OVER and OVER. I read this huge article that the reason they went to timed vacuum was emission reasons and manifold vacuum is fine.

I dont know. I mean, i got guys on here that say manifold, a few techs that say manifold. A few that say timed. ahhaa. Im damn lost with that.

Re: Carb issues, just chime in.
 

When you say your timing is 32 degrees at 3000rpm does that mean with vacuum degrees added on.
A quick curve is timing comes up real fast right after idle and slow curve means timing comes up slowly up to when your timing is all in.
Ported or manifold. Every motor is different. You gotta experiment.