Camaro-3

Hello,

I have a 84 Camaro (Canadian model) with the M4ME Quadrajet (Mechanical, not computer controlled).

2 Years ago, I rebuilt the quadrajet with an AC delco kit (by prevention). Before rebuilding it, I viewed a step by step video to make sure all was OK.

The engine was running good for 2 years and I adjusted it with a vacuum gauge. Sometimes, it was sputtering a bit and idles low when the car was ''Between cold and warm'', but it was'nt a big deal. The number of turns of the 2 idle mixture screws were 2.5 turns each.

1 month ago, the car started to idle high when warm (1500-1600rpm instead of 700-800). It was dieseling when shutting it off (warm), probably because it was idling too high.

3 weeks ago, I decided to check for vacuum leaks and I wasn't able to find one. I checked the carb adjustment and found a different trick to adjust it : When warm, you choke the carb with your hand and if it idles higher, it's too lean. And if it sputters or stall when choking it by hand, it's too rich. When choking it, it idled higher even when warm, so I unscrewed the idle mixture screws.

According to this adjustment trick, I unscrewed the idle mixture screws by 4 turns from 0 (instead of 2.5), and it was perfect for 2 weeks... And the sputtering/low idle between cold-warm stopped.

Last week, the car started to idle high again (1600-1700 rpm when warm!). I must stop the engine in gear now, because it is dieseling like crazy if I shut off the engine with the key at this rpm. Also, the engine stalls when I choke the carb by hand.

So according to me, it's running too rich. So I screwed the idle mixture screws to 2 turns each (instead of 4 turns). Now, it idles 1000-1100 rpm when warm instead of 1600 just before....

According to you, what could be the problem? Do you have any advice or could you suggest me to check some things to diagnosis the problem?

I have another quadrajet carb in my shelf, coming from a junkyard. Maybe I could rebuild it and install it... But not sure if it's a good idea to try it without rebuild. The accelerator pump of the carb from my shelf have a 'dry' noise when pressing on it. And the gaskets seems dry too.

NoEmissions84TA

iTrader: (1)

It still sounds like a vacuum leak. Check the base gasket to start with.

naf

iTrader: (7)

It cannot idle too high unless it's getting enough air. so it's getting too much air...don't worry about the mixture now.

the extra air is getting in either through a vacuum leak, the throttle blades or a passage somewhere within the carb.

first I'd do is ensure the throttle is resting on the curb idle set screw when it's idling high, if not I'd find out why. usually it's either the choke holding it up or worn throttle bushings binding.

Next I'd plug every vacuum port on the carb and manifold, or plug them one at a time while it's idling high, see if there's a change

I'd probably repeat that process to double check before opening the carb.

Camaro-3

The Choke mechanism on the passenger Side is sticking each time i blip the throttle. Its not the Choke plate itself but the throttle plate which is sticking but the problem is on the Choke Side (passenger). When it Isles too high and I press on the mecanism manually on the carb, the idle go down and it runs good until i blip the throttle again. However, its hard to see which part of the mecanism is wrong... I attached the mecanism with a paper clip to run it this week without Choke, until it Will ne repaired.

Also... The carb leaks gas at the outside from the aluminium plugs, especially front one Near filter.

Anyway, I plan to rebuild my spare carb with an ac delco kit (17076028) . Have bought one yesterday.

Do you know other carb kits with the throttle Shaft bushings? Is it necessary to replace it, or you think parts from the ac delco kit are enough??

And Also, which kind of JB Weld (epoxy) exactly Do you use for the carb plugs ? (Outside and inside ones).... I have Seen 3-4 types of JB Weld at the store... I prefer to try JB Weld instead of removing the plugs and tapping the holes...

naf

iTrader: (7)

the choke mechanism can stick, especially if the green Teflon coating has worn away from the little moving pieces. a good spray with WD-40 or some other lubricant can loosen them up.

check the bushings by removing the return spring, opening the primary throttle slightly and feeling for any play front to rear.

a carb kit won't come with a bushing (you usually only really need to replace the one on the primary shaft, throttle side. you'll need a drill press (or a really, really good hand) to drill out the hole for the bushing, there's also a kit that will otherwise guide the drill.


I've used regular JB Weld in the past, not sure which 'types' are offered now. not something I use much anymore.

Camaro-3

Replaced it for the other carb I rebuild. Carb stopped leaking outside, but the problem is still There.

Sprayed carb cleaner around and the rpm don't rises at all. The vacuum reading at idle is 20 hg at 800rpm.

The problem is the rpm. It jumps up and down erratically at idle. I need to unscrew the mixture screws at 6.5 to 7 turns to stop this idle bouncing. Is it normal?

NoEmissions84TA

iTrader: (1)

This may not be a carb problem. Look under the distributor ROTOR at the springs and weights to see if they are clean and moving freely.

Camaro-3

I Will check the distrib springs, but I doubt its the problem, because I had rebuilt the distrib 2 years ago. It was a Summit racing kit.

Is it possible it's not the carb itself, but the carb adjustment? I have not touched the Power piston screw adjustment of this New carb, since i have Heard it's hard to adjust it. But maybe it could have Been a good Idea to remove the plug on the top if the Power piston screw on the air horn to try to adjust it while running? But if I want to do that, i need to remove the carb air horn again. The float level is at 12/32 as needed for this carb number.

There is an interesting thread about off idle transition problems... the say it's possible the carb us switching from idle circuit to power circuit because of the adjustment. I tried different positions of the idle speed screw and of the idle mixture screws. Regardless of the idle speed screw position, i need 7-8 turns on both mixture screws to make it idle correctly. If not, the idle seems to lollop from idle circuit to primary circuit.
https://www.aussiev8.com.au/holden-v...idle-lean.html

Do you think it's a good Idea to adjust the mixture screws at about 8 turns if it idle ok or it's too Much and a symptom of another problem?

Confuzed1

iTrader: (4)

I've never heard of needing to adjust the mixture screws out so far. I can see adjusting them out about 1-1/2 to two turns each, but never 7-8 turns. Probably going into the power circuit because of the RPM it's trying to idle at. With a vacuum gage hooked up to the intake, did you try starting out with each screw backed out 1 turn from seated and slowly back each out 1/4 turn at a time until you get best vacuum at idle rpm? Then once you do, turn them each back in 1/4 turn then readjust idle rpm with the idle screw. Surging can either be a vacuum leak (causing a lean condition thus the surge) or as said, one of the springs in the distributor advance might be stretched or fell off on one end. Worth a look at that too.

EDIT: A strong smell of fuel could mean it's running too lean (too lean to burn all the fuel) instead of rich.....most think the burning your eyes think it's too rich...sometimes it's just the opposite....I'd keep looking really close at vacuum leak(s) as a cause if it were me. Power brake busters can also leak. Take a vacuum pump to the line and see it it'll hold 10" of vacuum, check PCV valve, intake gasket (spray starting fluid or carb cleaner around gasket and listen for idle rpm changes)

NoEmissions84TA

iTrader: (1)

As was said above, if it never needed 8 turns before, then something else has changed -----> symptom of another problem.