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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 02-13-2008, 08:07 PM   #1
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Quadrajet cold start and idle problems

So I tore down my old carb and fixed the secondary jam (don't know how that happened) cleaned it all up and put it on the car. It was a -20 day and the car started up perfectly and idled from cold to hot perfect at a dead steady 750rpm. yesterday I tried to start it, and it would'nt start unless I pumped the gas and after it would start i had to rev the sh*t out of it to get it to start. so i checked it out and i forgot the screw that holds the arm inside the choke coil and it fell out (forgot what its called its an electric choke carb) so i put the screw in and put it back to together then it ran really good all day. Then last night i tried to start it and it barely started i had to pump the gas again and it ran bad with a high rough/weird sounding idle. My cold idle screw is all the way out and when the car starts the choke opens up about an 1/8" to 1/4" is it supposed to open up that far? also how much tension should i put on the choke? i tried everythigng i could think of but nothing worked also the snow by my exhuast was black. someone please help me out, i just orderd cliff ruggles book so this is probably my last q-jet question lol. Thanks guys
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Old 02-13-2008, 08:33 PM   #2
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Re: Quadrajet cold start and idle problems

The factory choke element is supposed to be non-adjustable. It's got a little square notch on one side that lines up with a tab in the housing right next to the forward-most retaining screw hole. And that setting should be PLENTY close to get an reasonably good choke operation and cold idle.

The choke plate opening immediately after startup should give you about 1/8" of choke plate opening (measured by laying a 1/8" drill bit straight up against the rear of the choke tower airhorn). If you think yours is too rich or lean remember that you can remove the air cleaner (plug the vacuum line going to it if so equipped so you don't get a vacuum leak) and fire it up when it's overnight cold. You can then manually open and close the choke plate to get it where it runs best- then adjust the screw on the vacuum canister arm to match that manual setting. Remember you only get one or two shots at this every morning before things start to warm up and the setting becomes meaningless.

Also, remember it's normal to have a higher idle speed when the choke is engaged- there is a "fast idle cam" built into the choke linkage that opens the throttle slightly when the choke is closed. It should fire and settle in around 1300-1400 RPMs within a few seconds (but a smooth high idle- not rough like yours). The fast idle cam adjustment speed screw is underneath the choke linkage on the pass. side of the carb, viewed from the front of the carb. Adjustment screw is usually a small torx-head screw.

Last edited by Damon; 02-13-2008 at 08:36 PM.
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Old 02-13-2008, 08:42 PM   #3
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Re: Quadrajet cold start and idle problems

Thanks, but could it have been the tension that i had the choke at that it making the car run like this? I't ran amazing for 2 days until that stupid arm fell off..
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Old 02-13-2008, 10:52 PM   #4
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Re: Quadrajet cold start and idle problems

Hey Death, you seem to be having NO LUCK at all with q-jets eh?
Damons advice there is spot on, give that an adjustment.

Also, i'm going up to Edmonchuk on saturday afternoon. I'll be passing through Red Deer if you want to meet up, if you're still having problems.
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Old 02-13-2008, 11:19 PM   #5
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Re: Quadrajet cold start and idle problems

No luck at all!! are you driving the firebird or do you park her through the winter? Sounds good i'm stuck at home until monday just give me a call on saturday and let me know when youll be coming through town.
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Old 02-13-2008, 11:42 PM   #6
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Re: Quadrajet cold start and idle problems

oh god no, if there's a smidge of gravel on the road I can't get any traction - snow is a joke.
With the cam and the stickshift traction is a nightmare.
I'm driving my silver '92 Olds delta 88 through the winter.

PM me with your cell number, and preferably a first name, it's a little awkward using a persons screen name in person.
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Old 02-14-2008, 01:55 PM   #7
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Re: Quadrajet cold start and idle problems

Fiddled around with it today it starts runs for about 5 seconds at about 500rpm then dies, then when i try to start it again it won't start unless i touch the gas. Its the most frustrating thing ever.
----------
I wonder if it's a fuel problem?? it was running soooo good the other day

Last edited by creepingdeath; 02-14-2008 at 01:57 PM. Reason: Automerged Doublepost
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Old 02-14-2008, 01:59 PM   #8
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Re: Quadrajet cold start and idle problems

It's your choke blade setting most likely.
Play with it, but i'll be rolling through there at about 1pm on saturday and i'll show you what's what.

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Old 02-14-2008, 02:22 PM   #9
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Re: Quadrajet cold start and idle problems

I'ts not the choke blade.. it opens up 1/8' inch and stays like that. the lower screw is backed out all the way... And i'm getting fuel so i can't possibly see why the f*cking thing won't stay running. I've been trying everything but the car still dyes and sounds weird unless i hold the throttle wide open. The car won;t even stay running long enough for me to jump out and see if i can;t figure anything out, it seems to die as soon as i touch it. I'm getting sick of these carbs their peices of sh*t but i gotta get this thing started and running today or i'll have to find another way to work tommorow. I just don't understand this..
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Oh, what should the fuel look like when it comes out when your looking down into the carb? mine is squirting two streams of solid fuel i thought it was supposed to be foamy or atomized.

Last edited by creepingdeath; 02-14-2008 at 02:24 PM. Reason: Automerged Doublepost
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Old 02-14-2008, 02:39 PM   #10
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Re: Quadrajet cold start and idle problems

Ok i got tranportation now so ill leave the car alone until saturday.
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Old 02-14-2008, 02:47 PM   #11
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Re: Quadrajet cold start and idle problems

No, it'll squirt gas down.
The screw on the lower left side is the cold idle speed. Don't back it all the way out, turn it in until.... ah what the hell, it's so much easier to show you. Just chill for a few days man.
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Old 02-14-2008, 02:51 PM   #12
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Re: Quadrajet cold start and idle problems

sounds good.. I got alot of work around the farm to do today so i dont want to be screwing around with it anways.
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Old 02-17-2008, 03:26 PM   #13
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Re: Quadrajet cold start and idle problems

If anyone reads this in the future we got it running! it wasn't the carb at all, my distributor moved and my timing was super retarded. I hate reading threads without finding out what went wrong...
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Old 02-17-2008, 03:45 PM   #14
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Re: Quadrajet cold start and idle problems

Well, not entirely.
That thing has 494,000 kms on it!!!!!
Anyway, the PCV->carb hose was cut, so I plugged that at the carb. I opened the hot idle a lot to compensate, until he gets a new hose.

It blew a fireball out the carb once (had to put that out). I cranked the distributor wayyyyy over to advance so it would start. It's running nicer now but far from perfect. He needs to grab a timing light and set that, then reset idle speed and mixture.

That carb is fine though, it's in great shape. I think you can toss the rear vacuum break if you so wanted though.

When do you plan on putting in the Vortec 350?
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Old 02-17-2008, 04:28 PM   #15
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Re: Quadrajet cold start and idle problems

Ya i got the hose yesterday I'm gunna fine tune the timing tommorow after work. I plan on getting the vortec saturday after next . I got the pvc hose and I lowered the hot idle and cold starting is great, it runs at about 1500 rpm cold then once i tap the throttle she goes down to 750 i just took it out for a rip and it struggles a little after 3000 rpm tommorow it should run better.
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Old 03-19-2009, 09:52 PM   #16
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Re: Quadrajet cold start and idle problems

Anyone care to post pics of which screws are the "cold idle" and "hot idle" screws? I've searched google for the past 20 mins and can't seem to find any pics? I think I know which one is the warm idle screw?...
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Old 03-20-2009, 01:39 AM   #17
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Re: Quadrajet cold start and idle problems

Thanks for posting the solution to the problem, it really makes it a learning experience for us all.

449,000 kms, pfft its a chevy. whaddya expect :P

I got a questoin for sonix, If your timing is to advanced will it make cold weather driving harder, because i remember when i first got my car (305 quadrajet) that it drove so well in the cold, it felt like a fuel injected car. Then as time went on, things got changed, it sometimes stalls on me if its too cold and i dont let it warm up enough.

Ive got my timing at 8* and it sometimes pings so i know i should back it off a degree or 2, but would having a more retarded timing give better cold stability?
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Old 03-20-2009, 01:39 AM
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