High Idle and bad Idle Mixture Screw?
Thread Starter
Junior Member
Joined: Sep 2022
Posts: 9
Likes: 0
From: AUSTRIA
High Idle and bad Idle Mixture Screw?
After rebuilding my 1981 carb and reconnecting every hose my car "runs" again and idles around 1k - 2k.
If I screw the idle mixture screw (all the way in or 3 turns out - how many 360° turns can you make before you unscrew it?) there is no difference. I can't reduce the idle speed (counter clockwise rotation) anymore or the car will die.
Car seems to "swing" around and almost wants to die but then holds itself again and revs high.
I thought I adjusted everything according to the manual but apparently I am missing something.
How does changing the mixture affect my idle?
If I screw the idle mixture screw (all the way in or 3 turns out - how many 360° turns can you make before you unscrew it?) there is no difference. I can't reduce the idle speed (counter clockwise rotation) anymore or the car will die.
Car seems to "swing" around and almost wants to die but then holds itself again and revs high.
I thought I adjusted everything according to the manual but apparently I am missing something.
How does changing the mixture affect my idle?
Full Member
Joined: Sep 2022
Posts: 79
Likes: 19
From: Texas
Assuming you have a Nikki carb, directly quoting forum member Sterling:
Idle SPEED screw...located under the linkage on the right side, very low, and hard to see. Requires a very long flatblade driver.
Idle MIXTURE screw...located dead center driver's side of the throttlebody (cast iron lower part of carb).
Run engine and get it warm. Fuel behavoir is subject to temperature. Tuning a cold engine does no good when it becomes warm.
You are tuning the IDLE only. Tuning the idle has no effect on anything over 2000 rpm.
Adjust the idle SPEED to anything below 1000 rpm.
If you cannot get below 1000 rpm, you have a vacuum leak...a cracked hose, dried-up gasket, that sort of thing- It's letting air come in to the idle circuit, and bleeding off the signal to the fuel source.
Next, adjust the MIXTURE screw by turning it clockwise till it wants to stall. This is leaning the idle mixture.
When it starts to "hunt", or stumble, turn it back 1/2 turn.
Redirect your attention to the idle SPEED screw, and turn it counterclockwise untill you are idling at 750 rpms.
Return to the idle MIXTURE screw, and adjust it the same way as before.
Check the idle SPEED again, and if necessary, repeat both steps.
Your done.
A vacuum leak will only cause an incorrectable high idle.
It will not cause a stumbling.
If you are experiencing stumbling during idle no matter how many times you adjust it, and if you can hear it as you slowly rev the engine, then this is most likely an ignition problem
https://www.rx7club.com/1st-generati...e-carb-310927/
Idle SPEED screw...located under the linkage on the right side, very low, and hard to see. Requires a very long flatblade driver.
Idle MIXTURE screw...located dead center driver's side of the throttlebody (cast iron lower part of carb).
Run engine and get it warm. Fuel behavoir is subject to temperature. Tuning a cold engine does no good when it becomes warm.
You are tuning the IDLE only. Tuning the idle has no effect on anything over 2000 rpm.
Adjust the idle SPEED to anything below 1000 rpm.
If you cannot get below 1000 rpm, you have a vacuum leak...a cracked hose, dried-up gasket, that sort of thing- It's letting air come in to the idle circuit, and bleeding off the signal to the fuel source.
Next, adjust the MIXTURE screw by turning it clockwise till it wants to stall. This is leaning the idle mixture.
When it starts to "hunt", or stumble, turn it back 1/2 turn.
Redirect your attention to the idle SPEED screw, and turn it counterclockwise untill you are idling at 750 rpms.
Return to the idle MIXTURE screw, and adjust it the same way as before.
Check the idle SPEED again, and if necessary, repeat both steps.
Your done.
A vacuum leak will only cause an incorrectable high idle.
It will not cause a stumbling.
If you are experiencing stumbling during idle no matter how many times you adjust it, and if you can hear it as you slowly rev the engine, then this is most likely an ignition problem
https://www.rx7club.com/1st-generati...e-carb-310927/
Thread
Thread Starter
Forum
Replies
Last Post
finishline
2nd Generation Specific (1986-1992)
15
Nov 15, 2006 02:45 PM
O 16581 72452 5
1st Generation Specific (1979-1985)
10
Jun 24, 2003 11:07 PM