Thread: very high idle problem

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I just rebuilt my quadrajet carb for my 327 and put it back on this morning. Had all the adjustments per the rebuild kit (from NAPA), but it wouldn't start. So I messed with a few things but didn't really change anything except the idle screws at the throttle body. I turned them in from where they were. The next time I turned the key the engine fired right away and idled up to like 5000 rpm (really high, I don't have a tach). It wouldn't go down until I shut the engine off, and I tried everything I know to try and influence it, but the only thing that would change anything was to screw those idle screws out, but then it wouldn't start again.

So what's the deal? I even disconnected the throttle linkage and backed out the idle adjustement screw so the throttle blades should've been closed. But it's still running rich (lots of smoke) , and it's acting like it's getting a lot of fuel. Any ideas on where to start? Anything sound funny (like backing out idle screws causes it to not start?)?

Here's a good read for ya http://vetteworks.tripod.com/Qjet.htm

i rebuilt my edelbrock last month the first time in
18 years,it runs perfect after the rebuild, but i
remember my friend had a similar problem with
his holly the problem was when he installed the
new rubber plunger onto the excelerator pump
he did not put a thin layer of oil on it and it bound up.
it sucked air around the pump and it kept getting to
much fuel. the rebuild directions tell you to add a thin
layer of oil before assembly you probably did this but
i thought i would mention this. did it run before you rebuilt
it?

Also did you remember the pump discharge ball and weight?

viking, thank you for that site. I read over that while I was rebuilding it and got everything within spec, but that's a good reference site.

dotgone, I didn't know about the thin layer of oil in the accelerator pump as the directions I got didn't really mention anything. It was just an exploded view that you had to reference to get the thing back together, no written directions.

Pump discharge ball - if you're talking about the little ball valve, yes I got that. It didn't have a weight associated with it (maybe I'll recheck that), but it did have a pin that held it down.

Thanks guys, I'm pretty new at this stuff, so bear with me while I learn

Oh yes it ran fine before (except didn't respond well to throttle mashing and some gaskets were shot) and I can't figure out what changed between then and now. I'll just have to play with it some more. I hope it's as simple as accelerator pump plunger getting stuck.

Okay, so it was idleing (idling?) too high because I was stupid. So got that fixed now, but it still idles higher than I like. I'm pretty sure it has something to do with vacuum at this point. When I hit the throttle the secondary valves in the air horn don't open (held shut by vacuum), but it delivers a lot of fuel and makes a bunch of smoke (running rich flavor). So are there some vacuum connections that I'm missing? It's a Quadrajet carb with a thermostatic choke. I see one vacuum hose (I think) coming from the distributor area, but didn't really investigate to find out what it was hooked to. I think this hose connects to an outlet on the side of the carb, but does anyone have any insights?

On another note, I broke a stud for the thermostat, but there's still a little piece of the stud sticking out, so if I shoot enough penetrating oil in it should it come loose at some point? Of are there other ways of extracting it?

Sorry for so many questions and longwindedness, just trying to sort out some things...Thanks in advance.

the secondary valves in the air horn are controlled by a spring(not vac.) on the right side of the carb at the betterfly shaft, and can be adj. to open when you wont it to. be sure the choke high idle screw is not to high and kicking off ok. sometimes the float will hang up on the qjs. tap on the side of the carb, and see if thats help. but the idle screws are not causing all of the problems youve got, screw them in all the way and then back them out 2 turns and go to something else, then when you fix the flooding you can go back and re-adjust.

Okay, some more questions:
From what I can tell there is linkage that opens the secondary throttle blades when the primaries get to a certain angle. This works unless the little pin prevents them from opening. So what conditions must be met so that the lever moves so that the pin isn't obstructed and the throttle blades can open? Is it just an engine temp. thing? Hope that explanation's not too vague.

Second: It's also my understanding that the carb will automatically go to high idle mode until the throttle is blipped, and then releases down to low idle mode. Is this correct? Does anyone care to explain how this works, and if it's not working, what should I look for?

Third: Facing forward from the carb, on the driver's side of the fuel filter inlet, there is a little opening and tube. Is this supposed to be plugged? Is this some sort of vacuum dealy?

Fourth: Is there supposed to be a (I assume vacuum) hose sticking starboard from carb that runs back toward distributor area?

Fifth: I gather that once the secondary throttle blades open the blades on the air horn will open as well. There is some linkage connecting the air horn blades to some sort of plastic cylinder, and while the engine is running this is alyways holding those blades closed, so even if I could get to the point that the secondary throttle blades open, the air horn throttle blades remain closed. What's going on here? What controls this vacuum signal?

Any help and suggestions would be greatly appreciated. Thanks in advance.

Other things I forgot:
When I screw in the two slow idle adjustment screws in the front of the carb, does that lean the mixture or richen it?

When I screw in the fast idle screw (starboard side of carb), does this increase or decrease idle rpm? How?

Thanks.

A few notes about the q-jet. Yes, you must tap the gas to release the choke when the engine warms up or else your choke will just stay on and the idle will get higher and higher. You must also tap the gas before you start to set the choke. Your secondaries are blocked shut by the choke and will not be available until after the engine warms up. If you fiddle with the linkages on the passenger side of the carb and pull back on the trottle, you should be able to release the secondaries and they will open.

Q-jets meter fuel based on vacuum? So if there were a vacuum leak, vacuum would drop and fuel output would be increased. If vacuum gets low enough, the power valve opens. This would cause the engine to run fast and rich, though I think it would be less of a problem as you opened up the throttle.

i was too lazy to completely read, everyones posts, but make sure your timing is on also... and to get that bolt out, tap it with a chisle to make a nice deep slot, and use a screwdriver

Never had any luck with the rochester carbs. In my opinion I would switch to a holley carb I could never get the choke's or air valves to work right. that's just my opinion though .Plus I alway's thought the holley's had more low end torque.

Okay, so the whole problem was vacuum related. So the rebuild kit came with like 100 gaskets, and I didn't know which ones I needed. I accidently used a gasket against the intake manifold that allowed air to seep in while the engine was running and fuel to flow out after the engine had stopped :- . So I took that gasket off, laid the metal plate on top of the manifold and voila - the holes were covered, put a thin gasket on top, bolted carb down and she started and ran like she was supposed to, except for she idles lower and lower over a period of about five minutes until she just stops on her own. Anyone have any hints? It's not quite like fuel delivery problem, cause it's real slow, and it's kinda new to me.

On the note of Holley vs. Rochester, a couple comments: Since this project is more to get the truck running again than to completely restore and fancy it up to be a street performer, and since it's being done on a college budget, and since I have two quadrajets to work off of, I didn't figure it was worth it to go that direction. Also I heard that Holley's are pretty delicate and don't like being backfired through, and since I've already backfired about half a dozen times, , didn't want to try my luck. Thanks to all who replied, now it's on to my brake issue!

ok that could all be choke related.... i'd say most likely its idling down because it is warming up.... your fast idle speed might need to be adjusted along with your regular idle

Sounds like the choke isnt pulling off properly. There was a recall on the choke pulloffs due to leakage. Run a direct feed from a vacum source. If it doesnt snap open, your choke pulloff needs to be replaced.