Help with Carb A/C Idle Up
- Thread starter soe lost
- Start date
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There's two idle adjustment screws for the carb that you can fiddle with at the back of the carb. Firewall end. The third adjustment screw on the valve cover side shouldn't be messed with.
The idle screw at the back of the carb that will adjust the idle speed is the screw that's the more difficult one to reach. The easy one to get at is to set fast idle speed limit - not what you want.
The idle screw at the back of the carb that will adjust the idle speed is the screw that's the more difficult one to reach. The easy one to get at is to set fast idle speed limit - not what you want.
- Thread starter
- #3
The difficult one used to affect the idle speed but it doesn't do anything anymore, and I think the easy affects the idle when the choke is pulled so I haven't played with that one.
The one Im talking about is the one in front of the sight glass: for some reason its affecting the idle.
Sounds like the idle up on the AC is engaged full time.
Pull the vacuum line off of the AC idle up diaphragm actuator to see if it will idle down.
Pull the vacuum line off of the AC idle up diaphragm actuator to see if it will idle down.
- Thread starter
- #5
Sounds like maybe the AC idle set screw has been turned way up/in to compensate for the malfunctioning idle adjustment screw (if that's even possible). Back off the AC idle up screw all the way so it's in-op and then see if the idle adjustment screw does anything. If not, the carb should be removed & inspected.
- Thread starter
- #7
The AC screw is at about 3.5 turns, and when it hits 4 turns the car stalls. I rebuilt the carb in December and everything was fine up until mid-April. I even took it on a 400 mile trip in late-March, and a 1,000 mile trip in early-April, without any problems. I took the carb off last week and didn't see any debris and none of the passages were obstructed.
The AC idle adjustment screw is only a throttle positioner. It's actuation (when working correctly) is no different than pressing down slightly on the gas pedal.
When it's working correctly, you could set it so that when the vacuum diaphragm is pulled, nothing happens, or you could set it to make the engine race at 2000 rpm. It -should- not be able to stall the engine.
What could be happening (just guessing) is the AC idle adjustment screw was used to compensate a very low idle, and when it's backed off, the engine stalls.
You've got to completely disengage the AC idle set screw from the equation. It shouldn't be influencing the engine. Back the screw all the way out (or in- can't remember) so that it's not increasing the idle.
If the engine won't run— that's pointing to the problem elsewhere in the carb. It seems that the AC idle adjustment is being used as a crutch to crank up the idle.
It shouldn't be used at all.
When it's working correctly, you could set it so that when the vacuum diaphragm is pulled, nothing happens, or you could set it to make the engine race at 2000 rpm. It -should- not be able to stall the engine.
What could be happening (just guessing) is the AC idle adjustment screw was used to compensate a very low idle, and when it's backed off, the engine stalls.
You've got to completely disengage the AC idle set screw from the equation. It shouldn't be influencing the engine. Back the screw all the way out (or in- can't remember) so that it's not increasing the idle.
If the engine won't run— that's pointing to the problem elsewhere in the carb. It seems that the AC idle adjustment is being used as a crutch to crank up the idle.
It shouldn't be used at all.
- Thread starter
- #9
I used to be able to turn it and not have any affect which is how I discovered that now it does have an affect. I never thought of it acting as a crutch but thats a good theory. If thats the case then figuring out why sounds like another mess. Do you have any possible ideas as to what, in or around the carb I should look at?
It's possible that the engine can't idle normally because of a new vacuum leak. Get the engine running (somehow) and check the vacuum w a vacuum gauge. Check all the hoses and where they connect. Vacuum should be near 20inHg at sea level.
