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Old 07-27-2012, 09:28 AM   #1
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Carburetor question


Morning ya'll. I have a 77 F100 pickup that I just put a new carburetor on. It's a re-manufactured version of the original. The truck runs great, but when I first start it, it idles really high until I hit the gas pedal and then it will sputter and die. Then I start it again, it idles really high, I hit the gas pedal, and then it sputters, but then stays at normal idle. I'm not really concerned about it stalling out, but why does it idle really high when I first start it? I'd really like to fix this. Thanks!

Jesse

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Old 07-27-2012, 10:15 AM   #2
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Carburetor question


There is probably a high idle to warm up the engine when starting cold. If that is a factory spec. carb, might see if a Haynes or other repair manual discusses how it should operate and adjustments. Or the manufacturer of the carb. might have instructions on their web site.

Factory shop manuals are the best, but those can be expensive. Libraries sometimes have these books.

If all else fails, the info will be at alldatadiy.com

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Old 07-27-2012, 11:28 AM   #3
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Carburetor question


Look for a vacuum leak.
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Old 07-27-2012, 11:45 AM   #4
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Carburetor question


How many RPM's is it running at with the choke on? Let the engine cool, remove air cleaner assembly and depress gas pedal. What step of the fast idle cam is the throttle falling on?

Is the choke pull-off getting and holding a vacuum? Is it properly adjusted? Been awhile, I think Ford used manifold vacuum to the pull off. Check the radiator shroud for a diagram. It should show any check or delay valves.
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Old 07-27-2012, 12:59 PM   #5
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Carburetor question


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Originally Posted by 47_47 View Post
How many RPM's is it running at with the choke on? Let the engine cool, remove air cleaner assembly and depress gas pedal. What step of the fast idle cam is the throttle falling on?

Is the choke pull-off getting and holding a vacuum? Is it properly adjusted? Been awhile, I think Ford used manifold vacuum to the pull off. Check the radiator shroud for a diagram. It should show any check or delay valves.
I'm not sure how many RPMs it's running at. It doesn't have a tach. What step should it be falling on on the fast idle cam? I'm not sure if the choke pull-off is getting/holding a vacuum nor do I know if it's properly adjusted. How do I check it? I do know that it's a remanned carb straight from holley and they adjust everything there when they rebuild them. It's a Ford Motorcraft 2150. The vacuum line on the choke pull off goes to a vacuum port on the back of the carb. At least that's how it was out of the box. And this truck is a 1977 so it does not have the sticker on the fan shroud anymore. Thanks!

Jesse
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Old 07-27-2012, 01:27 PM   #6
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Carburetor question


How did you set the carb up without a tach and vacuum gage?
You need to first use a timing light and check the timing
Once timing is correct you adjust the carb. Starting with base idle and mixture adjustments, then the choke, fast idle and unloader.

To set the mixture screws I use the lean roll method. Turn both mixture screws out 2 turns. Start engine and allow to get to operating temp. With a vacuum gage and tach hooked up back out each mixture screw (in small increments) to get the smoothest and highest vacuum at idle. Use the idle speed screw to keep the speed at the base speed. Once you get the smoothest idle, turn each mixture screw in (one at a time) until you get a 50 rpm drop, then back out 1/4 turn.
Reset base idle speed with the solenoid extended. Unplug and retract the solenoid and set idle speed approx 100 rpm lower with the idle screw.

Without specs, with tach, set fast idle speed at approx 1200 rpm on second step.

To check pull-off, use a vacuum pump, or look at it when the engine is started. does it pull in? Crimp closed the vacuum line to it, does it stay pulled in?
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Old 07-28-2012, 06:59 AM   #7
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Carburetor question


I would suggest finding a shop with an older mechanic and have him set it up would take him about ten minutes to have it running smooth...being there are no other issues.
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Old 07-28-2012, 09:12 PM   #8
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Carburetor question


Reading what you explained the choke needs to be set .Depending on your experience you can check some automotive sites to tell you how to do it and you can do it your self or like other said have a shop that knows what they are doing set it

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