Fast idle question
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,388
Likes: 42
From: Murrysville PA
Fast idle question
65 365 HP
I have a question on the fast idle. When cold, I give my car one pump to the floor and turn the key. It fires right up and will run at fast idle until you bump the gas again. If you don't bump the gas, it will remain on high idle. Is this normal? Should it stay on fast idle until warmed? Also if you don't bump the gas, should the idle step down on it's own without intervention? I was told that it should remain on fast idle for about a minute and then come done to a normal idle on it's own.
Which is correct? Thanks
I have a question on the fast idle. When cold, I give my car one pump to the floor and turn the key. It fires right up and will run at fast idle until you bump the gas again. If you don't bump the gas, it will remain on high idle. Is this normal? Should it stay on fast idle until warmed? Also if you don't bump the gas, should the idle step down on it's own without intervention? I was told that it should remain on fast idle for about a minute and then come done to a normal idle on it's own.
Which is correct? Thanks
Team Owner
Joined: Jul 2006
Posts: 22,193
Likes: 4,180
From: Kannapolis NC
It's a mechanical fast idle. It will not come down till you depress the gas. That relieves the pressure on the fast idle cam and allows it to move down to the idle that corresponds to the choke postition. So it goes lower as the car warms up, but will not drop until the gas pedal is depressed enough to allow the cam to drop.
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,388
Likes: 42
From: Murrysville PA
I spoke with the man who owned the car when it was judged. It received 4 topflight awards each with very high scores. He was telling me that when he went for the Duntov award, the judge failed the car because the fast idle didn't come down after about a minute. He suggested a carb rebuild so thats what he did. The car went on to win the Duntov.
If I pump the gas once when cold, it fires instantly. However if I touch the gas again, it will go down to a normal idle even if it seems it's not ready to do so.
If I pump the gas once when cold, it fires instantly. However if I touch the gas again, it will go down to a normal idle even if it seems it's not ready to do so.
Team Owner
Joined: Jul 2006
Posts: 22,193
Likes: 4,180
From: Kannapolis NC
If the fast idle slows too soon, you need to adjust the choke to stay on longer. The choke plate position determines the fast idle position. The answer to your original question stands: the fast idle does not slow on its own. You have to push the pedal to allow the fast idle cam to drop.
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Team Owner
Joined: Jul 2006
Posts: 22,193
Likes: 4,180
From: Kannapolis NC
There's also an adjustment screw on the fast idle ***'y. If that screw is backed way out, it may be allowing the idle to drop while the choke is still on. You can determine if that is happening by looking at the choke and fast idle cam adjustment screw as the car warms up. The screw should still be touching the cam until the car has warmed enough to idle normally without the choke.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Sounds like yours is working perfectly, best leave well enough alone.
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,388
Likes: 42
From: Murrysville PA
I hear ya. I richened up the choke a tad and it worked. The car started and when I bumped the gas right away, it still idled fine. As the choke opened, the idle dropped until it was fully opened and idled normally.
Race Director
Joined: Jan 2003
Posts: 17,695
Likes: 3,683
From: Central Arkansas
Many cars I have owned remained on fast idle until the accelerator was tapped, allowing the divorced choke to pull the stepped cam to rotate to a lower idle setting. However, a few - like my old 440 GTX have enough pull from the divorced choke to rotate the stepped cam to a lower idle setting without ever touching the accelerator. It can work either way. Polish the end of the fast idle screw and the steps on the fast idle cam and it may pull off of fast idle automatically if that is what you want.
