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Old 11-01-2020, 09:26 PM   #1
40-A Twins
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Default Why do I have to keep pulling the choke out ?

Hi new member here, Model A owner since 1979.
I have run out of ideas to get the motor in my '29 to run right.
Motor starts right up and runs ok for about 10 seconds, then begins to slow and starts sputtering. Pull and release choke and this cycle repeats for 3 to 5 minutes - which requires me to sit leaning over with my hand on the choke. After this long warm up phase it continues to run at idle without choking but always a little rough.
I assumed this to be either an intermittent fuel blockage or vacuum leak issue, so have done the following:
Added filter screen to fuel shutoff valve.
cleaned out fuel line.
Adjusted carb float level to 5/8".
Cleaned carb passages.
cleaned jets.
New throttle shaft - old shaft had wear.
New manifold gasket.
New intake gasket.

What else could this be ?
I have tried swapping the Zenith carb out for a Tillotson, but it still runs poorly.
Any ideas ?

Kevin
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Old 11-01-2020, 09:30 PM   #2
Tacoma Bob
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Default Re: Why do I have to keep pulling the choke out ?

Clogged gas cap vent. Loosen the cap and start the engine and see if that helps. Often times blowing compressed air around the inside of the cap will blow the crud out.
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Old 11-01-2020, 09:38 PM   #3
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Default Re: Why do I have to keep pulling the choke out ?

Could be that your fuel cap is not venting (blocked vent) or that you may have a radiator cap being used as a fuel cap. They look similar but the radiator cap is not vented.
Try loosening you fuel cap a few threads or remove it all together and see if that overcomes your problem.
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Old 11-01-2020, 10:01 PM   #4
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Default Re: Why do I have to keep pulling the choke out ?

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Originally Posted by Tacoma Bob View Post
Clogged gas cap vent. Loosen the cap and start the engine and see if that helps. Often times blowing compressed air around the inside of the cap will blow the crud out.
I soaked my cap in gasoline over night and blew it out with compressed air the next morning. A similar problem to yours was rectified immediately.
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Old 11-01-2020, 10:12 PM   #5
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Default Re: Why do I have to keep pulling the choke out ?

How far open do you have the GAV on warm up.
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Old 11-02-2020, 12:47 AM   #6
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Default Re: Why do I have to keep pulling the choke out ?

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See attached article.

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File Type: pdf Gas Cap-30-31.pdf (224.1 KB, 115 views)
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Old 11-02-2020, 02:14 AM   #7
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Default Re: Why do I have to keep pulling the choke out ?

Carb mounting bolts tight?
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Old 11-02-2020, 06:34 AM   #8
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Default Re: Why do I have to keep pulling the choke out ?

Make sure the two mating flanges at the carb and manifold connection are flat. Put a file on them to make sure. You will see the warp. Clean it up.
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Old 11-02-2020, 06:35 AM   #9
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Default Re: Why do I have to keep pulling the choke out ?

The last thing I can think of is a cracked intake manifold. Very hard to find, but they do crack and leak air.
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Old 11-02-2020, 09:04 AM   #10
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Default Re: Why do I have to keep pulling the choke out ?

Other info.


https://www.fordbarn.com/forum/showt...r+running+lean


Do a search, example "poor running lean" which the above was the 1st result, will give you tons of ideas.
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Old 11-02-2020, 10:11 AM   #11
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Default Re: Why do I have to keep pulling the choke out ?

Low fuel flow would be my guess, fuel valve on, gas cap not venting, you could remove the carb drain and test for flow, more than a baby food jar use a quart jar.
Let us know what you find!
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Old 11-02-2020, 10:58 AM   #12
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Default Re: Why do I have to keep pulling the choke out ?

I have seen a video where the GAV is 3/4 turn open. Then when warmed about 1/4 turn open. This will vary from A to A of course. I would open the GAV a little more from where you have it set now.....maybe a quick fix.
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Old 11-02-2020, 11:10 AM   #13
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Default Re: Why do I have to keep pulling the choke out ?

Quote:
Originally Posted by 40-A Twins View Post
Hi new member here, Model A owner since 1979.
I have run out of ideas to get the motor in my '29 to run right.
Motor starts right up and runs ok for about 10 seconds,n
Quote:
Originally Posted by Tacoma Bob View Post
Clogged gas cap vent
Quote:
Originally Posted by RUNNERBUN View Post
Could be that your fuel cap is not venting (blocked vent)
Methinks that even w/a blocked vent that it would run longer than 10 seconds.
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Old 11-02-2020, 11:22 AM   #14
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Default Re: Why do I have to keep pulling the choke out ?

I had the same problem on my 29 Roadster. I had cleaned the carb a number of times myself to no avail. Finally set it to Jim Bullock in Texas and it came back looking like brand new. Put in on and it runs like a top - NO problems at all. Might want to consider this if all else fails.
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Old 11-02-2020, 11:36 AM   #15
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Default Re: Why do I have to keep pulling the choke out ?

I had the same problem I had to constantly pull out the choke to keep the Motor running till it warmed up I found the tappet clearance to great from worn lifters.I ground the valves and replaced the tappets which solved the problem.Welcome to the Barn.
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Old 11-02-2020, 11:46 AM   #16
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Default Re: Why do I have to keep pulling the choke out ?

When you get the car to run, spray carb cleaner around where the manifold meets the block and carb to manifold. Try not to get any directly into the carb intake. If there is a vacuum leak in those areas the engine will stumble then recover. Where are you setting the GVA? How many turns out is the air needle adjustment? I set mine 1-1/2 turns out to start with. The idle circuit is fed from the well, are all the holes in the well clear? They are on the small side. Did you take the well out when you cleaned the carb? It could be plugged up.
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Old 11-02-2020, 02:03 PM   #17
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Default Re: Why do I have to keep pulling the choke out ?

Thanks for all the tips.
I started it up today with the gas cap off and no improvements, so we can rule out plugged gas cap.
I adjusted GAV from closed to open 1 turn trying to find a spot where it ran good but no big improvements.

I always drain the gas by removing the carb drain plug, and it dribbles out a good rate.

Exhaust stinks like it is running too rich.
Gas is dripping out the back of the carb so the float valve is leaky.

I aimed propane into the carb intake and it sped up. I was trying to use propane to search for manifold leaks but fan wash is probably diluting the propane too much to be useful.

I looked over the intake manifold when replacing the gaskets a few days ago and did not see any cracks. Manifold flanges looked good.

It runs just as poorly when I put a Tillotson carb on.

Is it time to open up the motor and check tappet clearances ?
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Old 11-02-2020, 02:51 PM   #18
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Default Re: Why do I have to keep pulling the choke out ?

RE "I always drain the gas by removing the carb drain plug, and it dribbles out a good rate."
It should run out not dribble even when just draining the carb. You may have the ferrule too far back on the inline at the carb. The line should stick out from the ferrule just about 1/16" of an inch. Also did you replace the screen at the inlet? It could be plugged too. Gas can run out the back of the carb when you over choke it, that is normal. Does not mean the float is bad or miss set. Now if it runs out by itself while the car is just sitting, that is different. With the fuel line disconnected from the carb, how is the flow then? It should be a strong steady flow, if not you have blockage up stream.
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Last edited by redmodelt; 11-02-2020 at 10:47 PM.
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Old 11-02-2020, 03:25 PM   #19
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Default Re: Why do I have to keep pulling the choke out ?

Quote:
Originally Posted by redmodelt View Post
RE "I always drain the gas by removing the carb drain plug, and it dribbles out a good rate."
It should run out not dribble even when just draining the carb. You may have the farrow too far back on the inline at the carb. The line should stick out from the farrow just about 1/16" of an inch. Also did you replace the screen at the inlet? It could be plugged too. Gas can run out the back of the carb when you over choke it, that is normal. Does not mean the float is bad or miss set. Now if it runs out by itself while the car is just sitting, that is different. With the fuel line disconnected from the carb, how is the flow then? It should be a strong steady flow, if not you have blockage up stream.
==============================================



Here is the Correct name of the small brass compression fitting that
fits on a fuel line to seal the line from leaking at the fitting.

It's name is "ferrule"




.
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Old 11-02-2020, 10:47 PM   #20
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Default Re: Why do I have to keep pulling the choke out ?

Changed the spelling, thank you
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Last edited by redmodelt; 11-03-2020 at 10:44 AM.
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