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Old 08-29-2010, 05:06 PM   #1
walls
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Default flathead stumbles on acceleration

I need a little help with a stock flathead-single 94-stock distributor, mech fuel pump in a 50 ford I just bought.

The carb has been cleaned, has stock jets and has a new fuel filter. The accelerator pump works. I haven't checked the timing yet or the points but i suppose that's my next stop.

The car hesitated when stepping on the gas. If I step lightly on the gas, it will make it up through the gears (slowly) but, if I stomp on it, it continues to stumble. I thought it was the float level. I set it to the correct level (it was a little low) and put the throttle plate lever linkage back in the middle position (it was in #1).

I hopped in the car and went down the road. All seemed well, the car accelerated perfectly. I thought I fixed the problem. I parked the car for about 5 mins, went back to the car and I'm having the same problem. The only thing that could have changed in that time would have been temperature and possibly the gas. Even though i have a filter I don't know the condition of the tank.

One other weird detail, someone wired in an electric fuel pump w/ a switch. I have no idea why.

Any thoughts?
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Old 08-29-2010, 06:51 PM   #2
35desoto
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Default Re: flathead stumbles on acceleration

It has a fuel starvation problem - sounds as though the accelerator pump on the carby has a blockage somewhere that clears at times and then re blocks its self . Your symptoms are in keeping with a lack of fuel at a time when the vacuum falls and there is not enough of a "signal" for the engine to draw more gas and the engine needs more gas - which it is not getting. Gotta say - head back to the basics and clean every little orrifice out
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Old 08-30-2010, 10:18 AM   #3
blown49
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Default Re: flathead stumbles on acceleration

Could be the flex fuel line at the inlet to the fuel pump inlet has collapsed or pluggage in the fuel line from the tank. Try running it with the electric fuel pump and see if that does anything for it (maybe that's why it was installed.)

I'd also change the condenser NAPA IH200 if 6 volt or FA66 if 12 volt.

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Old 08-30-2010, 12:21 PM   #4
two coupes
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Default Re: flathead stumbles on acceleration

Have you checked the vacuum-assisted power-valve?
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Old 08-30-2010, 02:09 PM   #5
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Default Re: flathead stumbles on acceleration

Have you checked the vacuum module on the distrubtor? They go bad and cause those symptoms.
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Old 08-30-2010, 03:50 PM   #6
walls
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Default Re: flathead stumbles on acceleration

Quote:
Originally Posted by two coupes View Post
Have you checked the vacuum-assisted power-valve?
How do you check the power valve? I'm assuming that since it's not at WOT it's not the valve. The plugs are not fouled either.

Quote:
Originally Posted by chappys4life View Post
Have you checked the vacuum module on the distrubtor? They go bad and cause those symptoms.
I have a manual on order but, in the mean time, how do you check the vacuum module? I guess you're saying it's possible my timing is off because my vacuum advance is not working?
Is that something that can work one minute and then not the next?

I have a few free minutes, I'm going to go out now and take a look at the car.
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Old 08-30-2010, 05:02 PM   #7
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Default Re: flathead stumbles on acceleration

Had problems with my single carb stock flathead - a Holly/Ford 94. Would surge at idle, have a miss, run rich, etc. Took the carb top back off and adjusted the float level again based on the specs in our rebuild kit. This seems to have eased or cured the problem in our case.
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Old 08-30-2010, 05:16 PM   #8
walls
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Default Re: flathead stumbles on acceleration

I just took it out for a spin again. It sputters in 1st, is fine in 2nd in mid rpm and seems to run fine in 3rd.
I'm going to pull the carb and clean it then go from there.
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Old 08-31-2010, 01:54 PM   #9
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Default Re: flathead stumbles on acceleration

yOUR SYMPTOMS ARE STILL LEANING TOWARDS A LEAN FUEL MIXTURE - COULD BE A VACCUM LEAK FROM A DISTRUBUTOR ADVANCE DIAPHARM LEAKING OR THE CARBY STILL OFF TUNE SOMEWHERE - KEEP LOOKING - ITS THERE SOMEWHERE.IN FIRST GEAR YOU HAVE THE HIGHEST DEMAND ON THE ENGINE AND AS YOU GO UP THE GEARS THAT LOADING ALTERS AND THE ENGINE DOES NOT RESPOND THE SAME HENCE YOUR "MISS" DISAPPEARING AS YOU CHANGE UP A GEAR
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Old 08-31-2010, 02:54 PM   #10
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Default Re: flathead stumbles on acceleration

I have a manual on order but, in the mean time, how do you check the vacuum module? I guess you're saying it's possible my timing is off because my vacuum advance is not working?
Is that something that can work one minute and then not the next?

I have a few free minutes, I'm going to go out now and take a look at the car.[/QUOTE]

I was told a way to test them is to pull the vacumm line and have someone rev the motor as you blow into the line. If it runs smooth for the test your unit is bad. If your not sure about the age of the distrubtor its a 20 part and really takes a lot of guess out of your problem.

What that part does is control your advance, when you get on the gas to accelerate and there is no vacumm pressure it advances the timing. So when your getting on it and it stumbles thats a good part to check. Had the same issue with mine until I replaced that part.
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Old 08-31-2010, 03:21 PM   #11
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Default Re: flathead stumbles on acceleration

I had a similar problem, resolved by replacing the power valve accessible between the bottom and middle segments of the carb.

I rebuilt my the 94 myself, it was a pretty worn out carb to begin with. The power valve would blow-out occasionally.

Later I rebuilt a replacement 94 after being fed up with the worn and leaky one. The replacement was a very good core --no leaks & blown valves since!
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Old 09-02-2010, 02:57 PM   #12
walls
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Default Re: flathead stumbles on acceleration

I rebuilt the carb last night. Everything looked good except there was teflon tape on the power valve. I haven't had a chance to drive it but, I'll post the results when I do.
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Old 09-02-2010, 03:08 PM   #13
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Default Re: flathead stumbles on acceleration

power valve.....its screwed into the body of the carb on the underside between the base and body.. if it were starving for fuel it would do it all the time...ITS THE POWER VALVE. all it takes is to cough a 94 once and that valve is gone. to adjust your float make sure the top of the float is level with the top of the bowl. is some case's just slightly less the top of the bowl.
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Old 09-02-2010, 04:08 PM   #14
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Default Re: flathead stumbles on acceleration

The teflon tape is a clue... the power valves that properly fit the 94 aren't available any more. The ones for the 4 bbl holley fit in the hole, but aren't machined to seal right. That's what the tape was for.

The problem is, teflon tape tends to slough off little hairs and pieces after a while, and clogs stuff up. Either use pipe dope or machine the power valve to fit right.
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Old 09-03-2010, 12:01 AM   #15
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Default Re: flathead stumbles on acceleration

Holley power valves are notorious for "blowing" and then there is no lenght of problems to fix - cause it can't be fixed till the power valve is renewed
Teflon tape eventually dissolves in our fuel down her - something called aromatics - so yes it will disintergrate and block other orifices etc
Sounds as though you have found the problem and it all adds up - good luck in fixing the power valve correctly
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Old 09-03-2010, 12:39 AM   #16
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Default Re: flathead stumbles on acceleration

i bet the power valve...
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Old 09-03-2010, 01:32 AM   #17
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Default Re: flathead stumbles on acceleration

I hate to beat a dead horse, fuel delivery... either acc. pump, or power valve
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Old 09-03-2010, 01:38 AM   #18
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Default Re: flathead stumbles on acceleration

Disconnect the distributor vac advance & cap off. Drive it & see how it does.
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Old 09-03-2010, 05:29 AM   #19
walls
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Default Re: flathead stumbles on acceleration

The rebuild kit I bought was from Mac's. Does anybody know if they come with the proper type power valve? It seemed to seat just fine.

I know there is a couple threads showing the differences between the new and old style but, I couldn't find them. I'll look again after I get home from work tonight.

Is it common for people who use 94's to carry extra power valves with them in case of similar problems?
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Old 09-07-2010, 12:19 AM   #20
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Default Re: flathead stumbles on acceleration

GET A STROMBERG 48 or 97!!!! i had the same problem with power vales and i went through 4 94's before i decided to spend the cash and get some strombergs. just my 2 cents...
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