Erratic idle question
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Junior User
Joined: Jul 2012
Posts: 67
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From: Athens, GA...it rocks.
Erratic idle question
Hey guys, I have a 73 F100, 390 V8, original 2 barrel carb (recently rebuilt), auto trans.
I had the carb rebuilt about 6 months ago. After the rebuilt, she ran somewhat smoothly, but still got rough every now and then. As of late, the truck has had a rather erratic idle. When I'm driving down the road, it runs fine. When I stop at a red light, I have to keep my foot on the gas to keep it from sputtering to a stop. I have set the idle higher for the time being, but do not want to keep it that high for a long time. I need to get this thing running right. Does anyone have any ideas as to what I should be looking for? I've checked for vacuum leaks and haven't found any thus far.
I did take it to a local shop and they "adjusted the screws," but that has not changed anything for the better...might have made it worse. Any help would be appreciated!
Ng
I had the carb rebuilt about 6 months ago. After the rebuilt, she ran somewhat smoothly, but still got rough every now and then. As of late, the truck has had a rather erratic idle. When I'm driving down the road, it runs fine. When I stop at a red light, I have to keep my foot on the gas to keep it from sputtering to a stop. I have set the idle higher for the time being, but do not want to keep it that high for a long time. I need to get this thing running right. Does anyone have any ideas as to what I should be looking for? I've checked for vacuum leaks and haven't found any thus far.
I did take it to a local shop and they "adjusted the screws," but that has not changed anything for the better...might have made it worse. Any help would be appreciated!
Ng
Senior User
Joined: Jan 2013
Posts: 210
Likes: 0
From: New Mexico
Hey guys, I have a 73 F100, 390 V8, original 2 barrel carb (recently rebuilt), auto trans.
I had the carb rebuilt about 6 months ago. After the rebuilt, she ran somewhat smoothly, but still got rough every now and then. As of late, the truck has had a rather erratic idle. When I'm driving down the road, it runs fine. When I stop at a red light, I have to keep my foot on the gas to keep it from sputtering to a stop. I have set the idle higher for the time being, but do not want to keep it that high for a long time. I need to get this thing running right. Does anyone have any ideas as to what I should be looking for? I've checked for vacuum leaks and haven't found any thus far.
I did take it to a local shop and they "adjusted the screws," but that has not changed anything for the better...might have made it worse. Any help would be appreciated!
Ng
I had the carb rebuilt about 6 months ago. After the rebuilt, she ran somewhat smoothly, but still got rough every now and then. As of late, the truck has had a rather erratic idle. When I'm driving down the road, it runs fine. When I stop at a red light, I have to keep my foot on the gas to keep it from sputtering to a stop. I have set the idle higher for the time being, but do not want to keep it that high for a long time. I need to get this thing running right. Does anyone have any ideas as to what I should be looking for? I've checked for vacuum leaks and haven't found any thus far.
I did take it to a local shop and they "adjusted the screws," but that has not changed anything for the better...might have made it worse. Any help would be appreciated!
Ng
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Junior User
Joined: Jul 2012
Posts: 67
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From: Athens, GA...it rocks.
Went out and tried to adjust it in the way suggested. I couldn't get a screwdriver in where the screw is directly behind the distributor...guess I need to find a long skinny one. I did adjust the screw on the front of the carb, on the left side. I noticed almost no difference moving it in or out. Is it important to start with the screw behind the distributor on this procedure? I set the screw that I adjusted back to where it was set by counting the turns it took to screw it all the way in.
Thanks for your help...I need to get this situation resolved, and the shops around here can't seem to dial it in. One guy told me I am "burning a valve" and that that was my issue...uhmmmm...yeah.
Thanks for your help...I need to get this situation resolved, and the shops around here can't seem to dial it in. One guy told me I am "burning a valve" and that that was my issue...uhmmmm...yeah.
Senior User
Joined: May 2012
Posts: 315
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Went out and tried to adjust it in the way suggested. I couldn't get a screwdriver in where the screw is directly behind the distributor...guess I need to find a long skinny one. I did adjust the screw on the front of the carb, on the left side. I noticed almost no difference moving it in or out. Is it important to start with the screw behind the distributor on this procedure? I set the screw that I adjusted back to where it was set by counting the turns it took to screw it all the way in.
Thanks for your help...I need to get this situation resolved, and the shops around here can't seem to dial it in. One guy told me I am "burning a valve" and that that was my issue...uhmmmm...yeah.
Thanks for your help...I need to get this situation resolved, and the shops around here can't seem to dial it in. One guy told me I am "burning a valve" and that that was my issue...uhmmmm...yeah.
Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
When adjustment of the mixture screws has no effect on the idle quality that's typically a tell-tale sign of a vacuum leak (unless your idle speed is set so high you're overriding the idle circuit).
You may have a vacuum leak at the intake gasket(s), detecting this leak on a FE motor can't be done with the usual methods...
Cover both pcv/breather holes with duct tape, if one or both pieces of tape "dimple" inward with the motor running you have a vacuum leak at the intake gasket.
Senior User
Joined: Jan 2013
Posts: 210
Likes: 0
From: New Mexico
Hey guys, I have a 73 F100, 390 V8, original 2 barrel carb (recently rebuilt), auto trans.
I had the carb rebuilt about 6 months ago. After the rebuilt, she ran somewhat smoothly, but still got rough every now and then. As of late, the truck has had a rather erratic idle. When I'm driving down the road, it runs fine. When I stop at a red light, I have to keep my foot on the gas to keep it from sputtering to a stop. I have set the idle higher for the time being, but do not want to keep it that high for a long time. I need to get this thing running right. Does anyone have any ideas as to what I should be looking for? I've checked for vacuum leaks and haven't found any thus far.
I did take it to a local shop and they "adjusted the screws," but that has not changed anything for the better...might have made it worse. Any help would be appreciated!
Ng
I had the carb rebuilt about 6 months ago. After the rebuilt, she ran somewhat smoothly, but still got rough every now and then. As of late, the truck has had a rather erratic idle. When I'm driving down the road, it runs fine. When I stop at a red light, I have to keep my foot on the gas to keep it from sputtering to a stop. I have set the idle higher for the time being, but do not want to keep it that high for a long time. I need to get this thing running right. Does anyone have any ideas as to what I should be looking for? I've checked for vacuum leaks and haven't found any thus far.
I did take it to a local shop and they "adjusted the screws," but that has not changed anything for the better...might have made it worse. Any help would be appreciated!
Ng
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