Calling all quadrajet experts

[72turbojet]

I replaced my holley on my 402 with a quadrajet I ordered from national carburetor and I'm having some tuning issues with it running rich. The carb is set up for a bone stock big block engine and I had to replace the power piston spring to match my cam which made it driveable but it still seems rich at idle. I tried adjusting the mixture screws and they are mostly unresponsive except I got my highest idle with the screws all the way in which leads me to believe too much fuel is coming in somewhere else. I could use any tips or ideas at this point because I'm pretty stuck

[D.PASSMORE]

What was the symptoms before you changed power piston spring? Did it idle rich before you did the work? What size jets and rods are you running?

[72turbojet]

Before I changed the spring it was extremely rich smoking at idle and would stumble if idle. Now that I have a softer spring it idles decent and is much smoother than before but it still isn't perfect. I didn't pay attention to what size jets were in there. If it helps any the rebuilder was supposed to use stock jetting which i wouldn't think would cause the idle screws to be ineffective even with a mild cam. It smells rich and still isn't as smooth and crisp as it should be at idle

[geezer#99]

If your mix screws are like that, then your primary throttle is to far open and you're idling on the power circuit. You need to get the throttle closed. One way is to maximize your initial timing.
Higher initial will speed up the idle allowing you to close the throttle and cover the transition slot.
Read this link on the transition slot.
It mentions a holley but yours is the same.
http://www.crankshaftcoalition.com/w...EI_distributor

So, what's your initial timing?

[storm9c1]

+1. What geezer said.

Adding more initial timing or using the vacuum advance connected to full manifold will bump up the idle, then you can back off the carb idle stop screw. After you do this, then you can readjust your idle mixture screws.

[72turbojet]

Originally Posted by geezer#99

If your mix screws are like that, then your primary throttle is to far open and you're idling on the power circuit. You need to get the throttle closed. One way is to maximize your initial timing.
Higher initial will speed up the idle allowing you to close the throttle and cover the transition slot.
Read this link on the transition slot.
It mentions a holley but yours is the same.
http://www.crankshaftcoalition.com/w...EI_distributor

So, what's your initial timing?

I don't think the initial timing is too low. I checked it today and it looks like it's set at about 24°btdc

[Wrenchbender Ret]

Does it have a new float. A heavy float or the float level set too high will cause this.

[geezer#99]

Originally Posted by 72turbojet

I don't think the initial timing is too low. I checked it today and it looks like it's set at about 24°btdc

You did plug off the vac advance line when you checked, didn't you?

[72turbojet]

Originally Posted by geezer#99

You did plug off the vac advance line when you checked, didn't you?

Yes I plugged it and checked it idling in neutral. I had a mechanic dial the timing in when I first got it since im new to this and he said he turned it up as much as he safely could so it doesn't sound like adjusting the timing is going to fix my problem but I'm out of options at this point. I'd hate to have to throw my money away and get another carb

[geezer#99]

A few things!

What rpm did you check the timing at?

You better check the accuracy of your timing tab.
http://www.crankshaftcoalition.com/w...op_dead_center

Check the secondary throttle plate isn't hanging up on the gasket.

[mike16]

maybe princess wiggles will come on here and educate us all in quadrajetanese

[Liz]

Originally Posted by mike16

maybe princess wiggles will come on here and educate us all in quadrajetanese

and this is helpful to the post or community how? Play nice..

[72turbojet]

Originally Posted by geezer#99

A few things!

What rpm did you check the timing at?

You better check the accuracy of your timing tab.
http://www.crankshaftcoalition.com/w...op_dead_center

Check the secondary throttle plate isn't hanging up on the gasket.

I checked it at around 600 rpm in gear. The secondaries feel smooth and don't seem to be hanging up on anything. I'll check the accuracy of the timing tab when I get a chance but I imagine it's pretty accurate since the last mechanic to adjust the timing advanced it as much as he safely could

[cableguy0]

Look down the throat of the carb and look for fuel dripping at idle. If the mixture screws are basically unresponsive your timing is wrong or its pulling air through the throttle plates or both. Mass rebuilt carbs especially quadrajets can be an issue. People that have no idea what it is they are working on and assembling parts for the most part. I would be suspect that the engine actually starts with the timing at 24 advanced at 600rpm without vac advance hooked up. It should be kicking back hard on the starter. You need to verify actual top dead center and make sure your balancer and timing tab actually match.

[crazy longhorn]

I will be another , to jump on timing (verify the TDC)....then look to shoot for 14-16 initial/ total around 36 on that BB. then add 8 to 10 degrees to the vac advance manifold vac. Cut the 'curve " all in 2800-3200, depending on what she likes....Longhorn

[72turbojet]

I didn't have this idle problem on the holley with its current timing setting, so would a different carb want different timing?

[cableguy0]

Originally Posted by 72turbojet

I didn't have this idle problem on the holley with its current timing setting, so would a different carb want different timing?

No.quadrajets are very sensitive to being rebuilt properly. If they aren't you end up with problems like what you are having now. The only way I would run a quadrajet and its still not terribly likely is to have a known good core and have a quadrajet specialist rebuild it.

[GRX]

Originally Posted by Wrenchbender Ret

Does it have a new float. A heavy float or the float level set too high will cause this.

Also wondering about the float. Is it new brass?

Cliff Ruggles (the Q-jet guy) stated recently that he has seen a great number of defective Brass floats recently. So many that he only builds with Nitrophyl now.

Might be worth taking it out and doing a bubble test to be sure.

[72turbojet]

Originally Posted by GRX

Also wondering about the float. Is it new brass?

Cliff Ruggles (the Q-jet guy) stated recently that he has seen a great number of defective Brass floats recently. So many that he only builds with Nitrophyl now.

Might be worth taking it out and doing a bubble test to be sure.

It looked like it was a plastic float and wasn't set too high

[Ironangel]

Originally Posted by cableguy0

No.quadrajets are very sensitive to being rebuilt properly. If they aren't you end up with problems like what you are having now. The only way I would run a quadrajet and its still not terribly likely is to have a known good core and have a quadrajet specialist rebuild it.

This is the gospel truth! I had two 350's on the stand, one rebuild, one 260HP crate. I purchased two Quadrajets through Summit, one was a rebuilt, jetted & metered for 350's, the other was JET reman with the "'stage II" mods for a medium performance cam, etc....The Summit Quadrajet was impossible to tune so I pulled it off and stuck the JET re-manufactured Quadrajet on and "wala!" Ran like a top!...That was two years and almost 20K miles ago and still getting 12mpg and runs strong! Meanwhile, the crate motor (still in plastic on the stand) gets replaced with a deal I couldn't refuse, a low mileage freshly rebuilt 1969 375HP SS-396 motor out of a friends 69 SS El Camino. I call Cliff Ruggles up and must have caught him a good day because after explaining what motor I had, and the (new) junk Quadrajet I wanted to rebuild. He say's "throw it in a box and get it here and I'll take a look at it"...Three weeks and $350 later the carbs delivered with all the parts he replaced. The main issue was the new bushings for the primary throttle shaft were misaligned, so he corrected that and jetted it for the 408 (bored .060" 396) with the cam, heads, and 22cc domed pistons. He explained all the details over the phone when he had "dialed it in" on a similar big block in a Camaro he had "for tuning"...The carb arrived the day before the Midwest Truck Nationals last fall, it went from box to motor and ran flawlessly from 0-6000 rpm! The only tuning I've done since is idle adjustments finding out what timing curve works with ported or manifold vacuum. (Still in school on that one) Local drag strip opens April 6th for testing & tuning...I'll add this, I've raced bikes in the past and have a full understanding and ability to jet and tune the various inline four carb racks. I can read plugs and use a vacuum gauge to max out a carbs flow ability. The Quadrajet however still eludes my ability to fully wrap my mind around them. They are probably the most complex carb out there rendering them difficult to understand and easy to screw up. I like em all, but the Quadrajet is at home on a GM V8 from the old school. They're a challenge, just like a beautiful woman, but when they're dialed in and them 2-1/4" secondaries open up, better hang on because it's "game on!" They even have a unique sound that no other carb makes when them trap doors open up...~Ghostrider~

[72turbojet]

I think I'm going to get a rebuild kit and hope i find something like a faulty needle and seat or something of that nature and if that doesn't do it then a different carb might be in my near future. Thanks for everyone's input btw

[geezer#99]

A few links for you.
http://www.digitalcorvettes.com/foru...ad.php?t=88376

Pay particular attention to the section in here regards the needle clip on the float.
http://www.crankshaftcoalition.com/w...4MV_carburetor

And one more.
http://www.vetteprojects.com/kstyer/quadrajet.htm

[72turbojet]

Before I cracked into the carb again I decided to check my fuel pressure and at idle the needle on the pressure gauge jumps back and forth from 6-9psi so I have two questions

Is it normal for fuel pressure to be that unsteady?

And I've read that more than 6-7 is too much pressure for a qjet so should I try a new fuel pump?
Thanks to all

[geezer#99]

It shouldn't be that unsteady.
You might want to install a fuel regulator you can set at 5 psi.
Just in case you change carbs in the future and need one.

[CCCC]

Good info on the Q-Jet here - I will need this someday. Thanks to those who contibuted.