| tbirdhandyman | -- 03-14-2015 @ 4:15 PM |
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I was 900 miles from home when my '41 Mercury convertible quit. We installed a new Carpenter 91-99 replacement carb. and a new '46 fuel pump. Returned home without any problems. I had ordered a Drake replacement 11A F/P as a spare for the trip, and it had arrived after I returned home. I installed the 11-A F/P and the carb started leaking gas from everwhere! I checked the F/P pressure and it was 5&1/2 lbs! I installed a pressure regulator with a 3&1/2 lb setting and the leaks stopped. The MPG dropped from 16 to 12 MPG, and car will not run smooth in high gear at a low speed, as when you are approaching a stop sign. I talked with a Drake Tech and they had never heard of my problem. Today I shortened the push rod and test drove the car with 3.8 lbs pressure. There was a slight leak at the carb, and the car jumps and jerks when you let off of the accelerator @ 10 -15 MPH. Do you think if I shorten the push rod further it might solve this problem? Tbirdhandyman
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| ken ct. | -- 03-14-2015 @ 4:27 PM |
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FP rod length should NEVER be messed with. Your diaphragm spring is too strong ,common problem with China made new pumps. Pressure needs to be in the 2 1/2 lb. range. If you changed the spring you wouldn't need the regulator. ken ct.
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| cliftford | -- 03-14-2015 @ 5:49 PM |
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I agree with the predeeding post. You still have more furl pressure than the carb. needle and seat can handle. get it down to 2 1/2 lbs. and I bet your problem will go away. some people do this by shimming up the fuel pump tower with extra gaskets.
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| ford38v8 | -- 03-14-2015 @ 6:40 PM |
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Ken's right again. Next post is wrong. Shimming the tower is the same as shortening the pushrod. Use the spring out of your old pump and you'll be good to go. Alan
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| Stroker | -- 03-15-2015 @ 6:16 PM |
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Ken and Alan are correct. To understand your fuel pump, think of it as a pressure regulator that also happens to pump fuel. Only the spring determines the output pressure. The carb's float valve controls how much fuel is actually delivered to the carb by allowing fuel to enter the bowl as long as it is at or under the design pressure. If the incoming fuel is above this design pressure, fuel will hold the float valve open, bypassing its' design function. So...a stiffer spring will push more fuel past the float valve. The only thing that counts is how much fuel is pushed into the carb, and the only factor to consider is the output pressure of the pump; which is only controlled by spring pressure. Lengthening or shortening the pushrod, or shimming the fuel pump stand up or down only changes the volume of fuel the pump can deliver per stroke. It does not affect the pressure, and the pressure is the heart of the problem.
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| TomO | -- 03-16-2015 @ 7:35 AM |
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Ken is correct. Do not mess with the pushrod length. The diaphragm in the fuel pump should travel the distance specified by Ford. This distance controls the amount of fuel that is delivered on each stroke of the rod. The diaphragm return spring controls the pressure that the fuel pump delivers the gas at. To reduce the pressure, the spring needs to be the correct length and strength. I would send the fuel pump back as defective and buy a rebuilt from a reliable rebuilder or try the new Offenhauser pump from Speedway Motors. I have had good luck with them in the past. As the banks tell you "past performance is no guarantee of future results". Tom
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| RAND | -- 03-19-2015 @ 7:48 PM |
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Send it to ken ct. He'll fix you up Randy This message was edited by RAND on 3-19-15 @ 7:51 PM
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| tbirdhandyman | -- 03-21-2015 @ 11:48 AM |
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Thanks for the correct information on my fuel leaking problem. To get away from the regulator in the line, I installed more gaskets under the tower, and while the pressure did stay down, you could not get a lock washer and a full nut on the tower. That is when I shaved some off of the push rod. I knew it was the wrong thing to do, but I did in anyway. I found a new F/P made in the USA, installed a new push rod and gaskets and got it running this morning. My pressure gauge shows 3.0 lbs, but it may be off a tad at this low reading. No leaks, and I will test drive it when the rain stops down here in Houston, TX. Thanks again for your input. Robert E. Tbirdhandyman
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| TomO | -- 03-22-2015 @ 11:21 AM |
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If the new pump works, please post the manufacturer so others can but one. Tom
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