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fuel pump mystery big block

furyus

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Hello, I have a 440 in the 64 Sport Fury in my avatar. Been running good for several years. Went to the Turkey Rod Run in Daytona. Car would misfire occasionally. Hit the gas, and it stalled. Pulled the 750 race Demon apart, cause I was getting a dribble out of the shooters. Put in a new needle and seat, reset float, and had to adjust the fuel pressure, as I have a Holley pressure regulator and gauge. Car drove fine on the trip home. When I looked at the gauge again, it was down to about 3.5 again. I put a different gauge on it, and it still read 3.5. Changed the regulator, and reset the pressure. it was putting out around 7.5 psi, which I thought was too high. The pressure kept falling back to 3.5 as the car ran longer. Tried to bring pressure back up, but it wouldn't. Also noted the fuel was lower in the sight glass. Smelled dipstick, no gas smell. I'm wondering if it's the pushrod is worn, and loses it's ability to move the fuel pump lever the proper amount when the engine warms up. Bear in mind, I've had this same setup on the car for over 10 years, with until now, no issues. Thanks.
 
I would check the fuel pump push rod my 63 had same problem and the push rod was worn I put a new one in its fine now
 
It's the Carter street/strip rebuildable mechanical pump. I'm hoping it's the pushrod, as the kit to rebuild the pump is $64...
 
i would probably rebuild it, happened to my barn find 440 10 minuets into the break in. looking at getting one. Are they any good?
thanks, Dylan
 
the mancini kits are junk. the push rod may be wore down but i'd have to wonder how you could get 7.5lbs with a short push rod,...? all diaphragm pumps will loose some pressure when they get warmed up/hot. usually a pound. before spending any money look very carefully at the lines and hoses feeding the pump. check the sock in the tank and any hose connections.
 
If the Mancini kits are junk, who makes a good one? Summit doesn't list one. My theory is the push rod is just short enough that it will produce pressure when cold, and when the engine gets warm it expands enough to make the rod too short. I will start the car again today to see if it does this. Although I have 1/2 in fuel line from inside the tank to the regulator, I still may have some blockage, and will check that before I rebuild the pump.

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i would probably rebuild it, happened to my barn find 440 10 minuets into the break in. looking at getting one. Are they any good?
thanks, Dylan

I will find out when I check everything out to find what the issue is. The pump is only 3 years old, so if that's the problem,
I wouldn't recommend it.
 
nobody makes a good rebuild kit that i know of. something to think about is the 1/2" line. not knowing "exactly" what you have i'll make some comments. first i think 1/2" is too large for those 3 valve pumps. the larger the volume in the line the more the suction vacuum will be reduced. secondly if you take the pump apart you'll notice that the inlet passage in the bottom bowl is only 1/4" i.d.; so what value is 1/2" line? i like the carter pumps, but i don't use the high pressure pump (i don't like regulators for drivers. just another part to wrong), and i take them apart and re-work them. take the push rod and measure it; it should be around 3.22". some of the newer rods are soft and wear out. if the rod is o.k. then take the pump apart for inspection. if the pump is o.k. then ditch the 1/2" line.
 
fuel pump push rod, I had the same problem.
 
i did a little math and came to this conclusion. if one is comparing cross sectional area of .030" wall 1/2" and 3/8" tubing the 1/2" has twice the cross sectional area. i would think that would have to mean twice the volume and weight of fuel in the 1/2" line. the pump has a fixed displacement and the only variable would be the cam eccentric wore down or the push rod wore down. if those two are ok then it has to be the weaker vacuum draw on the larger tubing making it more difficult for the pump to pull the weight of the fuel; and keep in mind all the pump action on the suction side is pulled thru a 1/4" internal passage.
 
i did a little math and came to this conclusion. if one is comparing cross sectional area of .030" wall 1/2" and 3/8" tubing the 1/2" has twice the cross sectional area. i would think that would have to mean twice the volume and weight of fuel in the 1/2" line. the pump has a fixed displacement and the only variable would be the cam eccentric wore down or the push rod wore down. if those two are ok then it has to be the weaker vacuum draw on the larger tubing making it more difficult for the pump to pull the weight of the fuel; and keep in mind all the pump action on the suction side is pulled thru a 1/4" internal passage.
Ok, I verified that the pump pressure reads around 8-9 psi when cold. As it warms up, the pressure drops to 3.5. I will take a look at the eccentric on the cam, as well as trying a new pump push rod. If not, I will pull the sending unit, and make sure there's no blockage. I'll save the pump rebuild for last. I doubt it's the larger fuel line, as it's been this way for over 10 years, not counting the new pump 3 years ago. I will update this, as it may help someone else. Thanks for everyone's help.
I just checked the cam eccentric. Looks good, as far as I can tell. Don't have the equipment to measure it, but by cranking the engine, it looks ok, and I don't see any wear marks on it.
 
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could be something as simple as the pumps diaphragm has fatigued out. take the pump apart and look at it. i have a carter pump on my 69 r/t that i've been driving on for decades.


something else to think about; most of the common small regulators only have 7/32" flow orifices, and most are not designed for a pulse pump.
 
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lewtot184 is telling you the facts, new kits are not too good. Also are you adding zinc to oil to protect the cam and fuel push rod?

Yes, been using zinc oil. Good thought. If the new kits are bad, what is it that's bad about them? Not being a smart azz, just need to know so I can work with it.
 
the diaphragm didn't fit and the valves were very crummy in the kit i bought. i finally got the diaphragm to "fit", did a test on the pump and couldn't get anymore than 3.5lbs cold. real junk. would have been better off putting the money towards a new pump. some of the stuff mancini sells isn't real good.
 
the diaphragm didn't fit and the valves were very crummy in the kit i bought. i finally got the diaphragm to "fit", did a test on the pump and couldn't get anymore than 3.5lbs cold. real junk. would have been better off putting the money towards a new pump. some of the stuff mancini sells isn't real good.
The same is true with Summit Racing. If you buy from them, stay away from their house brand stuff.
 
I went threw the Carter rebuild deal a few years ago. Only place could find a kit was Mancini, bought it and was junk. Diaphragm was too big no holes lined up. Called Mancini and got the "never had problems with them" song and dance. Returned the kit and got a new pump.
 
Well, my update is, No, it's not a worn push rod, No, there's nothing blocking the pickup. No the fuel filter is not a restriction. I looked at the cam eccentric in my motor. It seemed to be a little hard to tell if it was eccentric. I looked at pics online, and the eccentrics look much larger than mine. I guess I will be going to an electric pump......
 
Are your problems worse as the temperature rises?

I ask as I have similar issues but are heat related. I put it down to todays fuel being far more volatile...
 
I went threw the Carter rebuild deal a few years ago. Only place could find a kit was Mancini, bought it and was junk. Diaphragm was too big no holes lined up. Called Mancini and got the "never had problems with them" song and dance. Returned the kit and got a new pump.

Interesting. I received the same kit from Mancini and emailed them a scale diagram of their diaphragm and the actual pump body, showing the incorrect size and hole location. Was told the same thing; "Never had a problem." I, too, bought a new pump. Do you think it's a ploy to sell new pumps?...lol. I love Mancinis, but I believe they should have opened a kit and a pump after the first complaint...
 
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