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Old 07-15-2020, 05:18 PM   #1
sofield
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Default Model “A” Bucking at 45 mph plus

Model “A” Bucking at 45 mph plus
The car is a “A” with indented firewall with a “B” engine, “A” head, converted to 12V, running a “B” carb and “B” distributor, 3.0-ohm coil, new condenser, cleaned points and replaced inline gas filter. The car idles well and runs well up to 42-44 mph. As speed is gradually increased to 50-55 mph the engine starts bucking and will to continue to buck until the speed is decreased to 42-45 mph again and then run well. The car has been driven 25 + miles at one time during the same day with the same response each time. A response to a solution from the members of the Ford barn membership is appreciated.
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Old 07-15-2020, 06:02 PM   #2
Jacksonlll
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Default Re: Model “A” Bucking at 45 mph plus

Not getting enough fuel into the carb bowl. I don’t know about B carbs, but if it’s like the zenith, your fuel line might be pressing against the screen in the carb.
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Old 07-15-2020, 06:27 PM   #3
WHN
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Default Re: Model “A” Bucking at 45 mph plus

Fuel problem.

I might start by takings apart and cleaning the carburetor. Check fuel lines and also the gas cap. Is there a air cleaner? If so, is it clean?

I think it’s something on the fuel/air side of you engine.

Enjoy.
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Old 07-15-2020, 06:43 PM   #4
Patrick L.
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Default Re: Model “A” Bucking at 45 mph plus

Yep, sounds like fuel starvation. Try loosening the fuel cap, may be a vent issue. At least its an easy first thing to try.
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Old 07-15-2020, 07:19 PM   #5
Mulletwagon
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Default Re: Model “A” Bucking at 45 mph plus

Does the shutoff valve on an indented firewall have a pencil filter like the earlier models ? If so, worth checking. Does sound like fuel starvation.
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Old 07-15-2020, 10:13 PM   #6
Johnny Nitro
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Default Re: Model “A” Bucking at 45 mph plus

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Are you using gravity fed fuel, or the “B” engine’s fuel pump?
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Old 07-16-2020, 05:47 AM   #7
bavArian
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Default Re: Model “A” Bucking at 45 mph plus

If it's a fuel problem I guess it should happen in 1st and 2nd gear as well if you reach high rpms, you could check that.
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Old 07-16-2020, 09:54 AM   #8
Ernie Vitucci
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Default Re: Model “A” Bucking at 45 mph plus

Good Morning...Just a thought, but check your point gap...Your rubbing block might have worn down a bit and your points are closer than 0.018. Could also be a sign of a coil that is a bit long in the tooth...same with your condenser. Ernie in Arizona
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Old 07-16-2020, 09:55 AM   #9
Purdy Swoft
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Default Re: Model “A” Bucking at 45 mph plus

I would check float height in the carburetor , Five eights is the correct float setting . If the float setting is too low , the engine will starve for gas at higher speed .
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Old 07-16-2020, 11:58 AM   #10
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Default Re: Model “A” Bucking at 45 mph plus

Agree float height.
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