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-   -   Truck won't idle after carb rebuild (http://www.hotrodders.com/forum/truck-wont-idle-after-carb-rebuild-220736.html)

hauss667 06-19-2012 12:48 PM

Truck won't idle after carb rebuild
 
So I was having major issues with my quadrajet and instead of taking on the daunting task of rebuilding a carb foreign to me in two days I decided to re-jet and rebuild a 650 carter afb I had laying around. So everything went smooth the floats are adjusted properly everything is in right but now the truck wont idle and you have to feather the gas to keep it going. It has no choke as it originally was off a circle track car and it ran fine on my 350 with no choke just a little cold blooded in the morning, but if i stick the choke closed now the engine idles but even if I wait until it hits temp as soon as I open the choke back up it sputters and dies

ap72 06-19-2012 01:02 PM

Take it apart and reclean it. And I mean make those passageways sparkle.

hauss667 06-19-2012 01:09 PM

I did that the first time lol carb acid baths and 100psi :thumbup:
Also I need to be at work in four hours :sweat:

ap72 06-19-2012 01:13 PM

try opening your idle feed, of that doesn't work clean it better. that carb doesn't care what time you work.

hauss667 06-19-2012 01:19 PM

I'll give that a try, I really dont think cleaning is an issue, this carb ran fine before it was just too big for my 305 so I only got the kit for the gaskets that I knew would get messed up trying to jet it.

ap72 06-19-2012 01:30 PM

this is from memory so bear with me.

Remove your primary boosters, there should be two small brass orifices in each one, clean the hell out of each one, the smaller one if your idle bleed, it needs to be spotless, and has a tendancy to fill with crud. Next follow that orifice through the main body, remove your idle screws and blast the passage ways clean with carb cleaner. When you set your idle feed screw go all the way in and back it out two turns to get a baseline, tune from there with a vacuum gauge. there is most likely crud in your idle bleed and no amount of magic acid pressure wash will take care of it if you don't know what you're doing. The other brass tube is your emulsion circut and should also be spotless for best cruise performance.

hauss667 06-19-2012 01:52 PM

No I meant I dipped the entire thing and blew all those out with compressed air, I got the thing to idle but now as soon as i put it in gear it dies. I'm not saying cleaning isn't the problem but the carb was in perfect condition before I tore it down and I spent an entire day cleaning and blowing out every orifice and crevice

ap72 06-19-2012 02:05 PM

You likely made it worse by blowing it, when crud gets wedged in there you need to pick it out with a fine wire and carb cleaner.

Btw soaking the whole carb is next to useless for functionality, you need to get in there with a fine wire and carb cleaner.

hauss667 06-19-2012 02:49 PM

I did that also, I used a section of wire from my mig welder, and I disassembled the carb completely to soak it

ap72 06-19-2012 03:11 PM

Well I'm betting its crap in the idle channel, there's really not much that can go wrong on these carbs, except get dirty.

cobalt327 06-19-2012 05:10 PM

Quote:

Originally Posted by hauss667
So I was having major issues with my quadrajet and instead of taking on the daunting task of rebuilding a carb foreign to me in two days I decided to re-jet and rebuild a 650 carter afb I had laying around. So everything went smooth the floats are adjusted properly everything is in right but now the truck wont idle and you have to feather the gas to keep it going. It has no choke as it originally was off a circle track car and it ran fine on my 350 with no choke just a little cold blooded in the morning, but if i stick the choke closed now the engine idles but even if I wait until it hits temp as soon as I open the choke back up it sputters and dies

It wouldn't idle better w/the choke closed unless it's getting extra air from somewhere other than through the airhorn. So it sounds like there's a major vacuum leak. Check the base gasket, the PCV hose and valve, and all the other vacuum ports and accessories that may be connected to the carb to see if you can isolate where the extra air is getting into the engine from.

Less likely but still a possibility is there's nowhere near enough fuel reaching the engine, so the choke needs to be used to get the air/fuel ratio rich enough to run. That could be from too low floats, sticking needle and seat, wrong or faulty gaskets, wrong jet/rod combination, too large air bleeds, etc.- but most of these things effect the idle a lot less than elsewhere.

What happens when you screw the idle mixture screws out? In? As in, do they change the idle at all, or are they unresponsive?

What did you jet it to? What was it originally?

ap72 06-19-2012 10:06 PM

A vacuum leak could also be the culprit, most of the rest isn't an issue at idle though, you can literally remove the rods and jets and an afb carb will still idle, the circut is completely independant.

hauss667 06-20-2012 03:54 AM

Sorry guys been tinkering with it and trying to get to work, it was, according to edlebrock specs, a 600cfm with 398 secondary jets and 395 primary jets the rod size escapes me. I jetted it down to a 500 and (again per edlebrock specs) used 395 jets for the secondaries and 386 jets for the primaries and I believe they are 65x42 rods (not positive) but I used their specs. If I adjust the idle mixture screws idle does adjust accordingly. Right now I have it idling but my mixture screws are out FOUR turns... This is un heard of to me... If I stab the throttle it will die, but if I feather it up then stab it it runs amazingly, picks right up, no dead spots. But if I drop it into gear it sputters and dies. I checked for vacuum leaks, nothing, I sprayed every vacuum hose, cap, and every gasket with ether and no change. I've heard stories of these airtex pumps putting out sub par pressure and I'm starting to wonder if thats my problem. I'll see if I can rig something up to check the fuel pressure as I live in the country and with my truck down have no transport to town lol

ap72 06-20-2012 07:31 AM

I have an edelbrock I run at 2psi... it has larger needles but it doesn't take much pressure. I'm willing to bet one of the idle circuts is now clean and the other is still clogged- if you don't have a vacuum leak. The idle air bleeds on the boosters always gave me problems and id start there. For revving up from idle try moving your accelerator pump rod into the hole closest to the pump, this will supply the most fuel when you hit the throttle.

hauss667 06-20-2012 02:29 PM

I tried moving the pump arm, it did make a difference in throttle response but to no avail. I did however notice that when I double checked for leaks some of the carb cleaner (I'm out of ether) pooled around cylinders 2 and 4 and was bubbling... I tried all the others thinking maybe it was just heat from the heads boiling it but none of the others did it... Have I found my deathly leak? I always assumed it would suck not blow if one of my intake runners were leaking :smash:


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