Alan B

New to this computer controlled carb scene and having some issues. Rebuilt the original 305 HO motor (L69) and added a mild Comp Cam, shorty headers and Trick Flow heads. Sent the Carb off to Jet Performance with a list of modifications and they rebuilt it and sent it back along with a new chip.
I cannot get this thing to settle in at idle without it eventually dying. I have changed the cap, rotor, plug wires and of course put new plugs in during the rebuild. I also installed a new O2 sensor. Jet Performance tech support listened and said they would call back but never responded.
At a loss, does anybody have any ideas? The only thing I haven't replaced is the ECM wiring harness. I can't seem to find a source for one.

sofakingdom

iTrader: (1)

Probably not the harness unless it's been butchered or is otherwise obviously coming apart.

Check Engine Light work? Any codes?

Alan B

Thanks for the response. There are no check engine lights or codes. I wouldn't think it would be the harness either but that is about the only thing I haven't replaced! Have not checked the float setting, I would have thought Jet would have got that right though.

sofakingdom

iTrader: (1)

Does the Check Engine light come on when you turn the key to On before starting it?

Alan B

Yes, there the check engine light comes on with the key until started.

erik69&85

iTrader: (1)

Some carb rebuilds are better than others... And not all circuits are controlled by the ECM. The idle circuit, idle air bypass, choke setting, min idle position can all be adjusted.

I wouldn't expect it to be perfect out of the box. You need to fine tune it.

I upgraded the cam on my LG4 years ago and stayed with a computer compatible cam... Had no issues once I fine tuned it.

Have you made any adjustments such as idle mix, choke settings, idle speed?.. state anything done to the carb once you installed it.

I always recommend a good reference on quadrajet if your going to have one... Cliff Ruggles' book is gold...

Alan B

I have adjusted the idle speed and the mixture screws. The choke, which is electric, seems to work ok where it is set. I originally ran the mixture screws about 5 turns out to keep it running. It was searching for an idle at that point and would puke all over itself when I ran over about 2800 rpm. That is when I changed the coil, cap, rotor and plug wires thinking it was a spark issue. That did fix the higher revving issue but the car just won't stay idling for more than 20 seconds - a problem with a 5 speed transmission as it would die when coasting. I adjusted the mixture screws all the way back in and started over at 2 turns out and adjusted up to 3 1/2 but it does the same thing.....idles for a bit and than just dies. Could it be a float issue perhaps? I would have to check and see what the setting is and what it is supposed to be.

sofakingdom

iTrader: (1)

See this other thread here, right below yours.

https://www.thirdgen.org/forums/carb...down-when.html

The mixture screws don't do anything. Nothing at all. Not sure why they even bothered to include them in these carbs. Set them to about 6 turns out and leave them alone.

All the idle adjustment is done with the IAB.

If the float had a problem, it would have other issues besides idling, since the float (fuel level) affects EVERYTHING in the carb. See my signature for a helpful bit of mental enlightenment. Concentrate on the words "fits" and "all the facts", with particular emphasis on "all". If ANY of the facts don't "fit" the proposed "explanation", the problem ISN'T the facts; it's the "explanation". That applies to the float in this instance.

Note that I am NOT saying "your float is fine"; NOT saying "don't bother checking your float"; NOT saying "floats don't cause trouble"; NOT NOT NOT NOT NOT NOT NOT. Don't put those words into my keyboard. What I AM saying is that the float, as a proposed "explanation" for why your car doesn't idle right, doesn't fit ALL the facts at hand. Assuming of course (yeah I know) that it runs well otherwise.

Adjust the IAB about a half-turn CW. If it helps, try adjusting it in more, a quarter turn at a time, until it quits making any difference. It'll help to hook up your dwell meter and verify that you don't run it beyond its useful adjustment range. If it isn't better by the time you run it in 2 full turns, put it back where it was and come back for round 2.

Alan B

Thanks brother! I got her idling......needs some tuning still but she idles, runs and drives!

sofakingdom

iTrader: (1)