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Old 09-07-2013, 03:36 PM   #1
Fritz
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Default Problems with new Mac's fuel pump?

I bought a new fuel pump from Mac's for my '41 pickup with a 239 and it seems as though it may not be keeping up? When I drive for a few minutes in any gear in the higher rpm range, the carb starts to choke itself out until I let up on the gas or shift.

It will also only run if I fill the carb float bowl up (one or two times) with gas. It seems then the engine will run long enough for the pump to actually start pumping. I have a clear in-line filter just before the pump, which gives me a visual guide to when gas is passing through to the pump.

Any ideas on what the problem could be? I could buy a rebuilt pump from Ken CT, but I want to see if anyone else had similar problems with new pumps, or if they had any other ideas?
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Old 09-07-2013, 04:01 PM   #2
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Default Re: Problems with new Mac's fuel pump?

Sounds like you may have a leaky flex line to fuel pump,the new alcohol fuel eats the old flex lines.Phil
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Old 09-07-2013, 04:16 PM   #3
JM 35 Sedan
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Default Re: Problems with new Mac's fuel pump?

What made you think you needed a new fuel pump, or what was going on with old pump?
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Old 09-07-2013, 04:24 PM   #4
Fritz
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Default Re: Problems with new Mac's fuel pump?

I have a new flex line (rubber, also from Mac's) from the main line to the pump. All the connections on it are tight...

I bought a new pump since the one on there hadn't been ran in 25 years, didn't seem to be working at all, and was extremely dirty. The engine was rebuilt last year. Just now getting all the bugs worked out.
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Old 09-07-2013, 05:07 PM   #5
L78CHEVELLE
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Default Re: Problems with new Mac's fuel pump?

I had the same problem a few years ago. I disconnected the gas tank and ran a fuel line straight to the pump from a exterior gas can. The pump worked fine. I replaced the new rubber fuel line I got from Mac's with a home made fuel line and the problem went away. Your situation may be different, but I would start with running a line direct to the fuel pump from and exterior gas source and see what happens. Check the vacuum on both sides of your pump and that will tell you if you have a weak pump. You can buy a vacuum gauge at any parts house cheap. From memory the vacuum from the tank side should be about 5 and the reading to the carburetor should be about 3.
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Old 09-07-2013, 05:13 PM   #6
Ken/Alabama
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Default Re: Problems with new Mac's fuel pump?

The last flex line I bought from Mac was just plain ol junk. It turned to mush in a very short time and you could rotate the hose in the fittings and that was allowing it to suck air. More offshore crap that will put you on the side of the road. I bought one for all my cars from Robert Shewman .
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Old 09-07-2013, 05:22 PM   #7
charles in east texas
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Default Re: Problems with new Mac's fuel pump?

Frex gas lines are advertised in the V/8 Times. Charles
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Old 09-07-2013, 06:26 PM   #8
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Default Re: Problems with new Mac's fuel pump?

If the pump works OK with a separate fuel source it could be the flex line or it could be something in the fuel tank partially blocking the stand pipe too.
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Old 09-07-2013, 06:31 PM   #9
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Default Re: Problems with new Mac's fuel pump?

WOW, I just bought a flex line from MACs. Haven't put it on yet and probably won't now! Is Robert Shewman the one who advertises in the V8 Times? I also bought a pushrod and intake gasket (60 hp). Anyone had experience with these items?
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Old 09-07-2013, 08:05 PM   #10
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Default Re: Problems with new Mac's fuel pump?

I am with those who are saying check your fuel pump by pumping from a source different than your gas tank or maybe from a temporary new line from pump to tank. I would do this with the FP mounted in place on the engine while cranking with the starter and ignition in off position. If the pump works well when pumping from a different source, then the existing gas line is obstructed or has a hole somewhere where air is being sucked instead of fuel. The Shewman flex hose is well made with quality brass fittings and hose that is impervious to this ethanol enriched gas. If by chance the FP does not pump from a separate source, make sure the FP rod is properly positioned in the cup at the end of the pump lever.
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Last edited by JM 35 Sedan; 03-19-2015 at 09:46 PM.
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Old 09-07-2013, 08:26 PM   #11
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Default Re: Problems with new Mac's fuel pump?

If it turns out that the pump is working properly then spend the extra $ money on the Shewman flex line. All too often we try to save a buck and it's just not worth it. We tend to step over a dollar to save a dime.
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Old 09-07-2013, 09:10 PM   #12
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Default Re: Problems with new Mac's fuel pump?

(A general warning for all as well as)
Fritz. If your old mechanical pump is as bad as it sounds, you should by pass it completely (I assume you are pumping through it)
If your diaphragm is old it won't handle the new fuel. One of the reasons a mechanical pump fails is because the diaphragm fails. If your diaphragm leaks, an electric pump pushing through it can fill your sump with petrol. Apart from the possibility of a big bang, the petrol will wash the oil from the engine, and cause an expensive seizure.
If you are running an electric pump I would recommend a complete bypass of the mechanical pump. The reason being that it is human nature to neglect that which we consider unnecessary , more so than we would if we were relying on it.
I have known of pumps failing like this when they were the only pump involved. The pump delivered enough petrol to the carb, while leaking into the sump, until the engine seized.
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Old 09-07-2013, 10:01 PM   #13
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Default Re: Problems with new Mac's fuel pump?

The fuel hose that you need is fuel injection hose (SAE 30 R9 is stamped on the hose). It can be purchased at most any auto supply store in various inside diameters and it is expensive! This hose is Ethanol resistant. If you buy regular fuel line hose (and this includes much of the imported hose and most all NOS hose), it will turn to mush fairly quickly.

The Ehanol problem is a "sleeping giant" and is one of the most difficult challenges that we face with our older cars. In addition to the hose itself, the diaphragms in fuel pumps need replaced and many of the electric fuel pumps are also not Ethanol resistant and can fail quickly.

Here are 2 pictures of an electric fuel pump that failed after car sat for about 2 years. We couldn't push any fuel through the hose by any means, as all the rubber parts had swollen up and completely clogged everything. We dissected this fuel pump with a rotary cutter.

Fritz47
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File Type: jpg Airtex2.jpg (129.3 KB, 75 views)
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Old 09-08-2013, 12:47 AM   #14
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Default Re: Problems with new Mac's fuel pump?

Quote:
Originally Posted by HCO41 View Post
WOW, I just bought a flex line from MACs. Haven't put it on yet and probably won't now! Is Robert Shewman the one who advertises in the V8 Times? I also bought a pushrod and intake gasket (60 hp). Anyone had experience with these items?
I also would not use a intake gasket from Mac's.i used one a few yrs back and took me 3 days of grinding and scraping to remove it a couple of yrs later. Get one from NAPA or an AP's store that handles "FelPro" gaskets/ Mac's was black. FP is a lite beige in color. OME. ken ct.
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Old 09-08-2013, 02:53 PM   #15
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Default Re: Problems with new Mac's fuel pump?

So the bottom line is that anything that is touched by today's gasoline must be either metal or a flexible material specifically designed for the ethanol. That puts a real crimp in getting original-looking flexible fuel lines.
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Old 09-08-2013, 03:16 PM   #16
ken ct
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Default Re: Problems with new Mac's fuel pump?

Yes it does but watcha gonna do. Or you can make your own with R9 hose and some barbed fittings or buy Shummens flex hose.Neither would look correct but the valve would look a little closer to stock it might get by a sloppy Judge.You can eliminate the USA rebuilt pump from the problem.There way better than any China made new one. ken ct OMO
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Old 09-08-2013, 04:30 PM   #17
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Default Re: Problems with new Mac's fuel pump?

Bob Shewman makes flex hoses with and without the check valve. G.M.
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Old 09-08-2013, 04:47 PM   #18
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Default Re: Problems with new Mac's fuel pump?

Quote:
Originally Posted by ken ct View Post
I also would not use a intake gasket from Mac's.i used one a few yrs back and took me 3 days of grinding and scraping to remove it a couple of yrs later. Get one from NAPA or an AP's store that handles "FelPro" gaskets/ Mac's was black. FP is a lite beige in color. OME. ken ct.
Wow, "3 days of scraping", Ken, what were you using for a scraper? LOL
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Old 09-08-2013, 06:26 PM   #19
ken ct
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Default Re: Problems with new Mac's fuel pump?

Yea 3 days it was like it was welded on there,came off in little pieces.Yea i know Sewman makes W an W/O valve the one W/O would look more stock. ken ct. It might get by a sloppy Judge or one that didn't care knowing good hoses are not made anymore except by BS.
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Old 09-08-2013, 06:41 PM   #20
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Default Re: Problems with new Mac's fuel pump?

Quote:
Originally Posted by ken ct View Post
Yea 3 days it was like it was welded on there,came off in little pieces.Yea i know Sewman makes W an W/O valve the one W/O would look more stock. ken ct. It might get by a sloppy Judge or one that didn't care knowing good hoses are not made anymore except by BS.
That's why I use nothing but grease on gaskets. Helps seal them and they don't stick to the engine or part. Try it. You'll like it.
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