292 Revival
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Lead Driver
Joined: Apr 2007
Posts: 5,958
Likes: 105
From: Houston
I will do that I did put a new vauum wiper motor on the car like three or four weeks ago maybe one of the old original hoses finally broke somewhere. I didn't mess with the car today but I do plan on pulling the carb off just to check the passages on the fuel circuits as well as to clean out the carb since it has been getting fine rust particles in it. I feel more comfortable doing this so I can rule out the carb for sure as I start looking for a vacuum leak.
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Lead Driver
Joined: Apr 2007
Posts: 5,958
Likes: 105
From: Houston
Went through the carb on Thursday at work. Was slow and boss wasn't around after lunch so I took a break and tore into the carb. Honestly what I saw still had me concerned as it was not that dirty inside. There was very fine rust particles throughout the carb but I blew everything out including the filter with carb cleaner and compressed air.
Threw it back on the car after work with the idle mixtures set to 3 turns from seat and once the bowl got filled up started up and ran smooth. Had to turn the idle speed screw down half a turn to take it back to its 800-850 rpm idle that it had before.
I don't think it was anything to do with the carb internally but I did notice the four nuts that held the carb down did seem a little loose. So its hard to say if the cleaning did the fix or reinstalling the carb and tightening down the carb after installation.
All I need to do is replug in the vacuum wiper hose to the power brake port on the back of the carb.
Threw it back on the car after work with the idle mixtures set to 3 turns from seat and once the bowl got filled up started up and ran smooth. Had to turn the idle speed screw down half a turn to take it back to its 800-850 rpm idle that it had before.
I don't think it was anything to do with the carb internally but I did notice the four nuts that held the carb down did seem a little loose. So its hard to say if the cleaning did the fix or reinstalling the carb and tightening down the carb after installation.
All I need to do is replug in the vacuum wiper hose to the power brake port on the back of the carb.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
THEN turn the idle mixture screws IN equally, the Idle RPM will increase, readjust RPM screw down to spec. Continue back and forth until idle smoooths out until no improvement can be had - maximum vacuum or RPM increase. With my truck, the sweet spot ends up with both idle mixture screws 1/2 turn out from fully seated for example.The idea is to make the carb work, we want maximum velocity and atomization of the fuel by leaning out the fuel/air mixture as much as practical. Another way to tell, the butterflies should be almost completely closed at idle. This is important.
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Lead Driver
Joined: Apr 2007
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From: Houston
The valves are almost closed all the way as it is now. I tried turning down to 2 turns out but engine wants to run rough. I could compensate by bringing the idle speed up on the screw but that will then open the valves enough to start bringing in fuel from the primary circuit.
Not sure if a 2bbl will be able to run on 1/2 turn but I can give it a try I believe right now I got it set at 3 1/2 turns on passenger side and 3 turns on driver side.
As far as the manual goes, that is out the window as this is a early to mid '70s Motorcraft 2100 2bbl carb. The manual would only cover the Holley 4000 which will help me greatly when I get around to rebuilding it so I can put it back on the car.
Not sure if a 2bbl will be able to run on 1/2 turn but I can give it a try I believe right now I got it set at 3 1/2 turns on passenger side and 3 turns on driver side.
As far as the manual goes, that is out the window as this is a early to mid '70s Motorcraft 2100 2bbl carb. The manual would only cover the Holley 4000 which will help me greatly when I get around to rebuilding it so I can put it back on the car.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Well every engine is going to be different, and also carburetors, production tolerances, etc. BUT, there is a stock setup starting point for that engine. Typically that will be plenty rich, and the needles are turned in for "lean drop". 3 turns out would have most idle mixture screws falling out? That just doesn't sound right. Hm.
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Lead Driver
Joined: Apr 2007
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From: Houston
I know it sounds excessive but I have unscrewed it 6 turns and they didn't fall out when I was messing with it before I took the carb apart to clean it again.
I do still want to try and get the rpm more rock steady and remove the vibration in the car itself which is more when its in gear. So I will keep that in mind and play with the settings some. Might try turning the idle mixture screws in and idling the speed up to see what that does.
I do still want to try and get the rpm more rock steady and remove the vibration in the car itself which is more when its in gear. So I will keep that in mind and play with the settings some. Might try turning the idle mixture screws in and idling the speed up to see what that does.
Cargo Master
Joined: Apr 2003
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The 800-850rpm idle speed sounds high. Do you have a manual for it? The correct idle speed will apply no matter the carb used.
You can tune the idle circuit with a vacuum gauge. Adjust the idle stop screw for the correct idle speed. Fit a vacuum gauge, and adjust the mixture screws in or out, until you have the highest vacuum reading. The idle speed will change while you do this. Re adjust the idle stop screw for the correct idle speed and repeat the mixture screw adjustment, again watching for the highest vacuum. Repeat until you've found the ideal setting.
As a test of the idle circuit, with the engine idling, you can screw one of the mixture screws all the way in. If things are good, the engine will die. If it keeps running, then you are getting fuel from someplace other than the idle circuit - a blown power valve or the equivalent, the throttle opened too far and activating the boosters, etc.
You can tune the idle circuit with a vacuum gauge. Adjust the idle stop screw for the correct idle speed. Fit a vacuum gauge, and adjust the mixture screws in or out, until you have the highest vacuum reading. The idle speed will change while you do this. Re adjust the idle stop screw for the correct idle speed and repeat the mixture screw adjustment, again watching for the highest vacuum. Repeat until you've found the ideal setting.
As a test of the idle circuit, with the engine idling, you can screw one of the mixture screws all the way in. If things are good, the engine will die. If it keeps running, then you are getting fuel from someplace other than the idle circuit - a blown power valve or the equivalent, the throttle opened too far and activating the boosters, etc.
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Thread Starter
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Lead Driver
Joined: Apr 2007
Posts: 5,958
Likes: 105
From: Houston
The 800-850rpm idle speed sounds high. Do you have a manual for it? The correct idle speed will apply no matter the carb used.
You can tune the idle circuit with a vacuum gauge. Adjust the idle stop screw for the correct idle speed. Fit a vacuum gauge, and adjust the mixture screws in or out, until you have the highest vacuum reading. The idle speed will change while you do this. Re adjust the idle stop screw for the correct idle speed and repeat the mixture screw adjustment, again watching for the highest vacuum. Repeat until you've found the ideal setting.
As a test of the idle circuit, with the engine idling, you can screw one of the mixture screws all the way in. If things are good, the engine will die. If it keeps running, then you are getting fuel from someplace other than the idle circuit - a blown power valve or the equivalent, the throttle opened too far and activating the boosters, etc.
You can tune the idle circuit with a vacuum gauge. Adjust the idle stop screw for the correct idle speed. Fit a vacuum gauge, and adjust the mixture screws in or out, until you have the highest vacuum reading. The idle speed will change while you do this. Re adjust the idle stop screw for the correct idle speed and repeat the mixture screw adjustment, again watching for the highest vacuum. Repeat until you've found the ideal setting.
As a test of the idle circuit, with the engine idling, you can screw one of the mixture screws all the way in. If things are good, the engine will die. If it keeps running, then you are getting fuel from someplace other than the idle circuit - a blown power valve or the equivalent, the throttle opened too far and activating the boosters, etc.
I honestly don't believe I can idle this engine down that far and I am confident that if I did the generator light would come on just idling. But I will give it a try and see if I cant idle it down to spec.
Logistics Pro
Joined: Mar 2005
Posts: 3,771
Likes: 80
From: tujunga, calif
It should idle 475-500 in neutral with no problem, if it won't you have a problem somewhere. Be sure to recheck the timing at that RPM, running at the higher RPM might have the advance unit advancing and giving a false reading if it wasn't disconnected.
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Lead Driver
Joined: Apr 2007
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From: Houston
Oh I can idle it down to 600 easily in neutral probably even 400. Just know that anything under 600 rpm and the generator light starts to flicker on.
Well I finally found my vacuum gauge will probably work on the car tomorrow during lunch.
I ran the car some and its not quite perfect on running weather is cooling up some so that might be part of it as the engine hasn't been running in cold weather so will be a first for me. But hope to get the engine running back smooth and if I can get it to idle down around 450 in gear I will.
Well I finally found my vacuum gauge will probably work on the car tomorrow during lunch.
I ran the car some and its not quite perfect on running weather is cooling up some so that might be part of it as the engine hasn't been running in cold weather so will be a first for me. But hope to get the engine running back smooth and if I can get it to idle down around 450 in gear I will.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
It's not so much of a problem as a quirk of generators. They just don't produce current at idle, so the regulator cutout disconnects to prevent backfeed. One reason alternators replaced them. It's true, the maintenance adjustments for carburetor tuning and such need to be done at idle spec.
Logistics Pro
Joined: Mar 2005
Posts: 3,771
Likes: 80
From: tujunga, calif
It's not so much of a problem as a quirk of generators. They just don't produce current at idle, so the regulator cutout disconnects to prevent backfeed. One reason alternators replaced them. It's true, the maintenance adjustments for carburetor tuning and such need to be done at idle spec.
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Lead Driver
Joined: Apr 2007
Posts: 5,958
Likes: 105
From: Houston
well I took and set my idle speed screw to half turn from fully closed I then used vacuum gauge and my tach/dwell meter to set the carb. Down side, I cant get the idle speed below 750 if I close the throttle plates all the way. Half turn out is 800 rpm. I do how ever have a very steady idle now and almost 19" of vacuum at idle that is steady.
I believe the only way I could get the idle speed to go down is to adjust the timing which I really don't want to do as the car starts too good and runs too good to go screwing with it.
In gear I am running right at 625 rpm in gear and no generator light.
I also turned one idle mixture screw in all the way, engine ran very rough and quickly stalled out. So the carb is set ideal based off what I have heard to date.
I believe the only way I could get the idle speed to go down is to adjust the timing which I really don't want to do as the car starts too good and runs too good to go screwing with it.
In gear I am running right at 625 rpm in gear and no generator light.
I also turned one idle mixture screw in all the way, engine ran very rough and quickly stalled out. So the carb is set ideal based off what I have heard to date.