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Old 06-01-2019, 02:40 PM   #1
Weaponsusmc
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Default 31 coupe will not go over 40 mph

My search feature isn't working. Could ya'll give me some tips on what to do or what to look for? Thank you
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Old 06-01-2019, 02:43 PM   #2
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Default Re: 31 coupe will not go over 40 mph

It also backfires when I shut it off
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Old 06-01-2019, 03:48 PM   #3
Patrick L.
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Default Re: 31 coupe will not go over 40 mph

Not too much info.
How does it run otherwise?
Where is the base timing set?
Where is the spark lever set?
Have you adjusted the GAV [ carburetor]?
Have you checked for fuel flow?
Have you checked the gas cap?
Is it also overheating?
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Old 06-01-2019, 04:08 PM   #4
Purdy Swoft
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Default Re: 31 coupe will not go over 40 mph

I would first check points gap and timing . Ford specs for points gap was eighteen to twenty two thousants . Most set at a happy medium of 20 thousants .
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Old 06-02-2019, 01:18 AM   #5
Brad in Germany
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Default Re: 31 coupe will not go over 40 mph

Another idea, have you checked the polarity of your coil....it might be reversed. You can easily check it using an ignition spark and coil tester like this one:
...from Brattons.

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Old 06-02-2019, 02:04 AM   #6
Charlie Stephens
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Default Re: 31 coupe will not go over 40 mph

Did you always have the problem or is it new? If it is new what was the last thing you did before the problem?


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Old 06-02-2019, 02:47 AM   #7
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Default Re: 31 coupe will not go over 40 mph

Has this motor always been like this or is the problem more recent. Are you sure the cam is timed correctly?
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Old 06-02-2019, 06:41 AM   #8
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Default Re: 31 coupe will not go over 40 mph

Check the throttle linkage, make sure the butterfly opens completely. Check timing, like it was said earlier too little info. All youre going to get are a bunch of basically worthless guesses, including mine.
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Old 06-02-2019, 07:02 AM   #9
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Default Re: 31 coupe will not go over 40 mph

Not much other info given about how car ran before, but many years ago we had a like problem. It was the carburetor. Popped and back fired over 35 mph.
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Old 06-02-2019, 07:05 AM   #10
Terry, NJ
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Default Re: 31 coupe will not go over 40 mph

I think you have not owned a mod. A for very long? Correct? How well does it start? Does it miss at any point in the RPM range? Does it do anything else? Did this just start? Did you just buy the car? Does it sound like it's over reving when you hit 40 MPH.
Some possible causes; Distributor malfunction, either something wrong inside or not timed correctly. Poor gas flow. Pedal not opening the butterfly all the way. Dragging brakes (The emergency brake is not fully released). The tires are not inflated enough. An outside possibility is that your cam timing gear has lost a tooth and it jumped timing. This is possible but check this last. Mod A s were designed to run at 60MPH and we hear of stock A s that will run at 70. So it's not that your car has reached it's design limits.
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Old 06-02-2019, 07:06 AM   #11
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Default Re: 31 coupe will not go over 40 mph

When you mention "backfire", does it sputter and backfire and loose power while driving?
If so I would pull over and open that gas cap. If you hear a hiss from the gas tank your cap vent is not venting properly.
I went through this recently and found that to be the culprit.

If not that I would do as suggested above and especially check the spark advance operation. Just my two cents worth, which could almost be considered worthless I guess. Please keep us posted, thanks. Chap
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Old 06-02-2019, 07:34 AM   #12
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Default Re: 31 coupe will not go over 40 mph

I believe the backfiring is when you turn off the engine. I think the timing may be off a bit. Backfire means you have unburied fuels hen you shut down. You could be running s bit rich and need to lean out the carb settings.
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Old 06-02-2019, 08:51 AM   #13
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Default Re: 31 coupe will not go over 40 mph

Running too rich and unburned gas collecting in the muffler . When the engine is shut down , the temperature in the muffler increases and if there is the slightest leak in the exhaust ,t the air from the exhaust leak sets of the explosion-backfire in the muffler
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Old 06-02-2019, 10:36 AM   #14
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Default Re: 31 coupe will not go over 40 mph

Your muffler could also be clogged? Remove it temporarily and see how it runs then.
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Old 06-02-2019, 05:41 PM   #15
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Default Re: 31 coupe will not go over 40 mph

you may well have a problem but please be aware that more lies are told about the size of fish and especially ones that got away. And more lies told of the yields of crops. And more lies yet again told about the speed of Model A's.
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Old 06-03-2019, 10:47 AM   #16
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Default Re: 31 coupe will not go over 40 mph

Check the condition of your spark plugs as well. If any are wet or showing signs of poor performance, they could also be a cause of unburnt fuel going out to the exhaust and running on less than 4 cylinders.This can also restrict your top speed.
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Old 06-03-2019, 02:48 PM   #17
1931 flamingo
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Default Re: 31 coupe will not go over 40 mph

Timing, timing, timing...................................


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Old 06-03-2019, 03:39 PM   #18
Charlie Stephens
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Default Re: 31 coupe will not go over 40 mph

Have you checked your speedometer, you might be going 80?

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Old 06-03-2019, 03:56 PM   #19
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Default Re: 31 coupe will not go over 40 mph

Here’s an easy thing to check that could cause your prob. Check the ferrule on your fuel line that goes into the carburetor. If more than about 1/16 in. of line is past the ferrule, it can hit the screen and restrict flow. Happens a lot.
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