Losing my idle
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Joined: Oct 2014
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From: AR
Losing my idle
I've got an 82 with 400 small block and a 750 Demon carb. After the car runs for 15 minutes or so, the idle drops and the car dies when I come to a stop or take a slow turn. What cause the loss of idle when it's good and warmed up?
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Joined: Aug 2016
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From: Denver CO
you set the base idle when the car is fully warmed up, so first guess would be the base idle is set too low, so when it comes off the choke its stalling out from not enough air. find the base idle screw and turn the idle up a few hundred rpm's so it doesn't stall when warmed up fully, then when its fully warmed up fine tune it to where its supposed to be.
edit* manual cars are set like 600 when in neutral, auto cars are set to like 550 when in gear per the sticker on the engine (although my auto likes a little more).
if after doing that you have issues with cold start rpm's then you also need to adjust the screw on the fast idle choke thing.
It could very well be something else, but I would start with making sure that is set right.
edit* manual cars are set like 600 when in neutral, auto cars are set to like 550 when in gear per the sticker on the engine (although my auto likes a little more).
if after doing that you have issues with cold start rpm's then you also need to adjust the screw on the fast idle choke thing.
It could very well be something else, but I would start with making sure that is set right.
Last edited by Ali Vette; Jan 20, 2017 at 08:02 PM.
Thread Starter
Advanced
Joined: Oct 2014
Posts: 73
Likes: 5
From: AR
you set the base idle when the car is fully warmed up, so first guess would be the base idle is set too low, so when it comes off the choke its stalling out from not enough air. find the base idle screw and turn the idle up a few hundred rpm's so it doesn't stall when warmed up fully, then when its fully warmed up fine tune it to where its supposed to be. manual cars are set like 800-1k when in neutral, auto cars are set to like 7-800 when in gear (usually goes to like 1200ish when in park).
if after doing that you have issues with cold start rpm's then you also need to adjust the screw on the fast idle choke thing.
It could very well be something else, but I would start with making sure that is set right.
if after doing that you have issues with cold start rpm's then you also need to adjust the screw on the fast idle choke thing.
It could very well be something else, but I would start with making sure that is set right.
Thanks for the info. The carb has just been rebuilt and did fine for the first 4 or five runs then the idle issue started. I know you turn the screw clockwise to increase the udle but how sensitive is it? A quarter turn for a couple hundred rpm's? Also, there's no choke on this one.
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Joined: Aug 2016
Posts: 99
Likes: 10
From: Denver CO
Dub is right I dunno what I was thinking on those rpm's I think I misread the sticker last time, just re-checked the sticker under the hood again and 600 is right. My engine has a cam in it and is a bit off tune so it likes more rpm's in drive or it gets upset, Its happy around 750ish you will hear where its happy.
Yeah to get it in the ballpark maybe 1/2 turn at a time since its stalling now, but to fine tune it I go about 1/8 to 1/4 at a time. you can get it close while its running also with the air cleaner off just don't let it hit your fan =) also make sure its warmed up and off the choke, give the throttle a blip to make sure before you do it.
Also make sure to re-adjust your throttle cable if necessary, more of an issue when lowering the idle though cause the cable can hold it at a higher rpm, increasing the idle should be fine if it was adjusted right at some point.
sticker on my '71
Yeah to get it in the ballpark maybe 1/2 turn at a time since its stalling now, but to fine tune it I go about 1/8 to 1/4 at a time. you can get it close while its running also with the air cleaner off just don't let it hit your fan =) also make sure its warmed up and off the choke, give the throttle a blip to make sure before you do it.
Also make sure to re-adjust your throttle cable if necessary, more of an issue when lowering the idle though cause the cable can hold it at a higher rpm, increasing the idle should be fine if it was adjusted right at some point.
sticker on my '71
Last edited by Ali Vette; Jan 20, 2017 at 08:10 PM.
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Joined: Aug 2016
Posts: 99
Likes: 10
From: Denver CO
Wait I just re-read that you don't have a choke on your carb... you probably have another issue going on then cause I want to say if your base idle screw (only adjustment on yours) is adjusted where its idling fine when cold, as it warms up the idle should go up quite a bit and not down. it could be a mixture issue then vs an idle setting issue.
Last edited by Ali Vette; Jan 20, 2017 at 08:18 PM.
Thread Starter
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Joined: Oct 2014
Posts: 73
Likes: 5
From: AR
Wait I just re-read that you don't have a choke on your carb... you probably have another issue going on then cause I want to say if your base idle screw (only adjustment on yours) is adjusted where its idling fine when cold, as it warms up the idle should go up quite a bit and not down. it could be a mixture issue then vs an idle setting issue.
I adjusted the idle up and it fixed the problem. Not sure why it's fine one day then off the next. Maybe vibration turning the screw or need a new screw or spring? Who knows but it's good now and I know how to adjust so I appreciate the info!
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