NEED some carb help

[85_SS_302_Coupe]

My car has got me stumped and i can't figure this one out. Basically it won't idle. It will only idle at or above 1500rpm, and it will drive and it runs awesome just like it always did, but if you downshift and run the rpm any lower than 1500 or so, it dies and then it's a bitch to start again. It's not starving for fuel because i can step into it and run it as high rpm as i want and it pulls like crazy, the damn thing just won't idle. I've checked every possible vacuum leak i can think of, i've bypassed the brake booster/PCV/vacuum advance and none of them have any effect. The float looks to be adjusted right...some have said that maybe the float isn't floating, but wouldn't that cause the bowl to flood? It's not flooding and i checked that by pulling the site plug while running. The fuel level DOES seem to be a little low, but again if it was starving for fuel i don't see how it runs so hard when driving it (and it's not just running off the secondaries...i can feel when they start opening and it'll pull good on just the primaries too). I also pulled off the front bowl and checked the needle and seat and they're not clogged or sticking and the float seems to be moving fine as well. I'm about at my wits end :(

[Black Horse]

Sounds like there might be some dirt in one of the internal carb passages. I would pull it apart, give it a liberal dose of carb cleaner, put it back together and see if that made any difference.

[85_SS_302_Coupe]

I was thinking crud in the idle circuit too.

[zlou363lx]

mine is now doing this too. i'm about to just park the car in the corner of the garage, and get to it sometime later this year lol

[85_SS_302_Coupe]

Must be something in the air because one day it was running fantastic and the next it runs like garbage.

[ascCapri]

I have been fighting my car as well, thought I had a miss.....replaced plugs, cap, rotor, dizzy, vacuum diaphragm, everything. Then I looked to the "newly rebuilt" carb and found vacuum leaks, both at the base and one of the vacuum ports. I can't tell you how funny this vacuum leak messed with the car and my brain. Trans shifted wierd, smelled fuel, chugged at idle.

I ordered a rebuild kit as well, and made sure it was done right. I have driven it the last 2 days with no major issue. I was getting terrible gas mileage, but think I may have figured it out. We'll see. Good luck!!

[85_SS_302_Coupe]

So i bought a gallon can of carb parts dip.

The main body won't fit into the can :doh:

Isn't that stupid?

So i got a can of good carb spray with a straw and blew out every air passage i could find. I've got the float weighed down sitting in a jar of water so i can see if it fills up and is leaking. If that's not the issue...and i've blown out the main body and metering blocks...what the hell could the problem be?

Is it even possible that the fuel pump could be starving it for fuel at idle yet still supply fuel for WOT? All the gaskets look fine, no tears or rips or anything like that. I can't imagine where a vacuum leak could be...and anyways wouldn't it raise the idle even higher if it had a vacuum leak? This thing will idle for a few seconds and just die like it isn't getting fuel.

[85_SS_302_Coupe]

I've ruled out the carb at this point after swapping it onto another engine AND swapping on another carb onto my engine and mine still stalls and my carb idles fine on the other engine. I shot a few videos of what it's doing...maybe someone will think of something i haven't.

http://www.youtube.com/watch?v=rgscxizZHe8
http://www.youtube.com/watch?v=270Uy9MrXHk
http://www.youtube.com/watch?v=o3oQXPuTwfI

[347sc]

Have you hooked a vac gauge to it and see what it reads? Might have an intake gasket leaking also.

[85_SS_302_Coupe]

Already put new intake gaskets in...the old ones look like new too.

[mailman]

I would try pulling some timing out, and checking the quality of your spark.

Also, turn the idle screw out way too far, and try to keep the engine running at a lower RPM using the accelerator pump. If you can use the acc. pump to make the engine run around 800-1000 by dancing on the throttle, you can assume that your problem is mixture related. However, it shuts off so quickly and cleanly when you idle down that I would think that the more likely culprit is ignition.

[85_SS_302_Coupe]

See that's just it...it won't idle down, it just stalls. I can back off the timing but that just seems to make it worse.

[PHAT69AMX]

What Holley Carb number ?
How many turns opened from fully closed is the Primary Idle Speed Screw ?
Might try opening up the secondary idle speed screw some.
Ideally, the Primary and Secondary butterflies should be opened the same amount.
If secondary is closed to far, and the primary is opened to far, it can sometimes act like you're saying.
Just a guess if it's not the ignition or a vacuum leak.

[85_SS_302_Coupe]

It's a 4150 mechanical secondary. The thing about the secondaries is that they haven't been touched since i don't know when...so i don't see where a before and after could've happened to cause what you're saying. I'll have to check on the number of turns for the idle screw.

[PHAT69AMX]

Is it like a 4776 600 double pumper or a 4779 750 double pumper, etc ?
What's the numbers stamped on the choke horn ? if it has a choke horn.
(2) Idle mixture screws, or (4) corner idle ?
How many turns out from gently fully seated on the mixture screws ?

[85_SS_302_Coupe]

I think it's 4777 but i'll have to double check. It only has the 2 front mixture screws and one power valve. The choke horn is removed but i have the numbers scribed on the main body.