Carburetor trouble on 89 justy

Carb was working ok except a little rich at idle. I pulled the carb off to change the thermostat, so decided to rebuild it. I put a carb kit in it and cleaned it all out. I thought it went well, but now it dies when the idle drops below 1500rpms. Idle speed is going from 3000 to 2000 by itself.
I’ve got the carb back apart and don’t see any problems. Just hoping someone can tell me what part of the carb is most likely the problem.
I’ve rebuilt the carb 4 times now without any trouble, and I thought this time was my best work.

Does it have a polymer float? Was it replaced?

Sounds like the idle circuit is plugged.
I’d take out the idle mixture screw and spray carb cleaner with an extension tube.
Should come out in the bore, float bore and one of the air passages.

Thanks for the input. After having the carb off 5 times today, I finally found a broken wire going to the anti-dieseling switch.
Good to go now. Thanks

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That sure would plug the idle circuit :wink:

Just curious, do you mean @circuitsmith that the throttle valve closing too far (b/c the a-d gadget isn’t holding it partly open when the engine is running) , that somehow it plugging off a port in the carb’s idle circuit? I can see that. Buy I don’t see how that would make the idle rpm vary between 3000 and 2000.

I see your point. Back in the day my '75 Civic had a solenoid & plunger that would close off the main jet to prevent dieseling.
So the OP’s car has a way to close the butterfly to get the same result?

My 74 Olds 350 had the solenoid and plunger that would hold the throttle open a little more when the key was on. When the key was off, the plunger would recede and allow the throttle to close completely, thus reducing dieseling. Seemed to work ok or you could break the plastic caps on the idle adjustment jets and richen the fuel a little.

Hopefully OP will post back how the Justy anti-dieseling solenoid works on that vehicle. On my Ford truck it works as @bing posts above for his Olds. It’s possible a throttle valve closing far enough would not just block the airflow, but also block off the little idle hole in the carb near the throttle valve seat which is used for gasoline to flow into the intake manifold at idle too.

When and if you ever have the carb off again you might consider removing the 3 Phillips screws on the bottom that attach the lower throttle body to the next section up; the float chamber housing.

'Run a large file across the mating surfaces of both. It could be you find one or both warped; sometimes severely. File until perfectly flat. Warped surfaces (very common) can allow fuel to leak internally or internal air leaks.

It’s a plunger type solenoid that blocks a passageway when its not getting power.
There is probably another problem with the carb because I’m getting poor gas mileage. Filing the mating surfaces sounds like a good idea.

Logic would support your comment. In the early ‘70s in response to the mandates from the newly formed EPA, manufacturers leaned the carbs out and raised the cylinder operating temps just enough to sometimes cause dieseling, at least until the float bowl ran out of gas. I can remember walking through parking lots and hearing that horrible sound accompanied by enraged owners. The idle stop solenoids were installed to totally choke off the engines’ air supplies by allowing the butterfly valve to close completely and seal off the carburetor throat when the key was shut OFF.

My '72 Vega came with an idle stop solenoid the bracket of which was prone to breaking from stress fracturing, and it would swing down on the wire into the accelerator linkage and jam it open. It happened to me. I had, fortunately, access to welders, and one of them welded the bracket and reinforced it with a gusset plate. Just weeks after I fixed mine a TSB came out for the problem. Vega had a lot of TSBs, and, as my luck would have it, they all seemed to come out a few weeks after I’d repaired the covered problem. :grin:

Interesting, so it is sort of an electronic controlled carb rather than just holding the throttle linkage open a little when the engine is running like my inelegant but functional truck’s anti-dieseling design. My parents had a Subaru of similar vintage and ran into a problem w/the carb that their mechanic could never figure out how fix. They eventually just sold the car to the mechanic. There seems to be some expertise here on the problem, for example from OK above. Keep trying, don’t yield to that stubborn carb. And keep us informed what you find. Best of luck.

The anti-diesel solenoids have been used on many types of carburetors over the years. Even the old air-cooled VWs have them.

When power is provided to the solenoid the needle retracts and opens the idle circuit in the carb body. Shut the key off the power goes away and the needle closes the circuit to prevent run-on.

As for Subaru, they had a lot of carburetor issues with their carburetors; but not according to them… :wink:

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On my Vega the solenoid when energized held the throttle plate at idle position and when deenergized the solenoid allowed the throttle to close fully. Sounds like VW took a different approach.

The VW approach was the same as Subaru, Nissan, Toyota, and most other European and Asian makes.

The solenoids are generally mounted in the carburetor body somewhere above the idle mixture screws.

If you look at an old air-cooled Beetle you may see a single wire harness routed around the top of the carburetor. There’s a single fuse in there which controls power to the ignition coil and anti-diesel solenoid.
Then again, the old VW air cools were not really prone to dieseling with a 6 to 1 compression ratio. Many people would remove the solenoid, discard the needle, reinstall the solenoid,and drive on.

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