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Old 03-08-2021, 03:09 PM   #1
dorvedahl47pu
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Default 40 Ford Flat 8 Idle Issue

Good day,

Here's what I've got. The engine starts with relative ease. Prior to start I put in a little throttle and a lot of choke. Once started I mess around with the throttle and choke to find the sweet spot. Choke is still mostly closed. Once warm I can lose the throttle but anytime I try to open the choke more than about 25%, the engine stalls out. I've put a rebuild kit into the Ford model 91-99 carb and have a newly rebuilt 11A distributor as well.

Is it normal to have to operate with a lot of choke at idle?

Thanks in advance.

Dale
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Old 03-08-2021, 05:26 PM   #2
51woodie
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Default Re: 40 Ford Flat 8 Idle Issue

I would suggest you have an air leak in the intake somewhere. There could be a leak in the intake manifold gasket, or the carb to manifold gasket. If there is a vacuum line to the wipers, it is possible that it has split or become disconnected. If you can get it to idle, take a hand held propane torch, turn on the gas (don’t light it), and pass it closely around the areas mentioned above. If the engine speeds up, there is the leak.
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Old 03-08-2021, 05:40 PM   #3
Mart
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Default Re: 40 Ford Flat 8 Idle Issue

Dale, can you reread your description because it seems to contradict itself.
You say it needs a lot of choke to idle but also say choke is almost closed.

I can describe what would be normal.

It might not need choke to start, especially if the accelerator gets a few pumps first, but choke will help if starting from cold.
Once warmed up, choke should not be used.
If you want a fast idle, the first part of choke operation will open the throttle somewhat and lift the idle. Beyond a certain point, however, the excessively rich mixture will hamper running and may even cause it to flood out and stop.

What is common is for a 94 to run over rich, due to many possible reasons. It will start readily from cold with little or no choke due to the over rich condition. As it warms up it begins to run poorly and will not tolerate the choke being applied at all. It may be difficult to start hot and requires the pedal to be held down while cranking to pump out the excess fuel and find a mixture that will make it fire.

Does your motor fit in with either of those scenarios?

Mart.
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Old 03-08-2021, 06:42 PM   #4
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Default Re: 40 Ford Flat 8 Idle Issue

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Originally Posted by 51woodie View Post
I would suggest you have an air leak in the intake somewhere. There could be a leak in the intake manifold gasket, or the carb to manifold gasket. If there is a vacuum line to the wipers, it is possible that it has split or become disconnected. If you can get it to idle, take a hand held propane torch, turn on the gas (don’t light it), and pass it closely around the areas mentioned above. If the engine speeds up, there is the leak.
Thanks...I will certainly give that a try. I've previously capped off the wiper exhaust since as you predicted it was junk.
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Old 03-08-2021, 09:51 PM   #5
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Default Re: 40 Ford Flat 8 Idle Issue

Quote:
Originally Posted by Mart View Post
Dale, can you reread your description because it seems to contradict itself.
You say it needs a lot of choke to idle but also say choke is almost closed.

I can describe what would be normal.

It might not need choke to start, especially if the accelerator gets a few pumps first, but choke will help if starting from cold.
Once warmed up, choke should not be used.
If you want a fast idle, the first part of choke operation will open the throttle somewhat and lift the idle. Beyond a certain point, however, the excessively rich mixture will hamper running and may even cause it to flood out and stop.

What is common is for a 94 to run over rich, due to many possible reasons. It will start readily from cold with little or no choke due to the over rich condition. As it warms up it begins to run poorly and will not tolerate the choke being applied at all. It may be difficult to start hot and requires the pedal to be held down while cranking to pump out the excess fuel and find a mixture that will make it fire.

Does your motor fit in with either of those scenarios?

Mart.
Mart,

Thanks for the tutorial! Here's what I did after work today. She started right up. She died a couple times probably due to my trying to adjust the throttle and choke knobs. I did get her to a good idle for about 5 minutes with the throttle knob pushed in but could never get the choke more than 50% open (guesstime based on choke knob position) without it wanting to die on me.

Dale
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Old 03-09-2021, 12:12 AM   #6
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Default Re: 40 Ford Flat 8 Idle Issue

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The idle screws on the carb should be open(turned out) around 1 1/2 turns from a seated position. Also turn the idle speed screw on the linkage in to increase the idle rpm. Give it some choke to get it started and don't mess with the throttle knob. Once you get it running, start opening the choke. If the engine won't stay running, adjust the idle stop screw further in. If you can't get it to run, there is a problem with the carb. If you have a vacuum leak large enough that the engine won't run, it should be audible.
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Old 03-09-2021, 06:18 AM   #7
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Default Re: 40 Ford Flat 8 Idle Issue

Dale, are you getting throttle and choke mixed up?
By throttle do you mean hand throttle or foot throttle?
If warm it shouldn't want to run with choke pulled all the way out.

Or do you mean it doesn't want to run above 50% throttle (pedal)?
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Old 03-09-2021, 07:01 PM   #8
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Default Re: 40 Ford Flat 8 Idle Issue

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Originally Posted by Mart View Post
Dale, are you getting throttle and choke mixed up?
By throttle do you mean hand throttle or foot throttle?
If warm it shouldn't want to run with choke pulled all the way out.

Or do you mean it doesn't want to run above 50% throttle (pedal)?
Mart,

I'm talking about the hand throttle adjustment. I have been giving it a little hand throttle before starting and backing off after it warms up a bit. It runs like a NASCAR engine with the foot pedal. Idling is the issue. It absolutely will not idle with the choke fully open. I'll try the vacuum leak test and play around with the idle adjustment needles. some more.
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Old 03-09-2021, 07:03 PM   #9
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Default Re: 40 Ford Flat 8 Idle Issue

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Originally Posted by flatjack9 View Post
The idle screws on the carb should be open(turned out) around 1 1/2 turns from a seated position. Also turn the idle speed screw on the linkage in to increase the idle rpm. Give it some choke to get it started and don't mess with the throttle knob. Once you get it running, start opening the choke. If the engine won't stay running, adjust the idle stop screw further in. If you can't get it to run, there is a problem with the carb. If you have a vacuum leak large enough that the engine won't run, it should be audible.
Good advice. I appreciate you sharing it with me. I'll see what happens.
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Old 03-09-2021, 07:10 PM   #10
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Default Re: 40 Ford Flat 8 Idle Issue

If you're using the hand throttle, is it not just an adjustment of the idle speed screw that is needed? It's the screw at the bottom of the lever that goes between the throttle and choke lever.
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Old 03-09-2021, 08:07 PM   #11
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Default Re: 40 Ford Flat 8 Idle Issue

I would not use the hand throttle at all when starting it cold, use your foot if you think it needs air (throttle) . keep in mind the choke also has a devise that also opens the throttle slightly to help keep the cold motor happy until it warms up a bit and smooths out.
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