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Fuel Pump - Scratching my head


James_Douglas
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On my 1949 Desoto I removed the factory mechanical pump and installed a Carter Rotor Vane electric.

 

As instructed by Carter, I ran a return line to the tank with a 3/32" fitting.  I was told that the pumps needed about 5 gallons an hour flowing through them to keep the motor cool.  I was told that the smaller engine classic cars that did not have the return line could overheat the pumps in parades and serious stop and go traffic and the return line is the optimum solution.

 

So, I have about 1000 miles on the car. I had a fuel problem the other day.  I suspect it is in the carburetor and I am working on cleaning and checking that carburetor. 

 

As part of my check, I decided to see if what the fuel pressure is doing.  I stuck a gauge on the end of the line were the "T" is to the inlet of the carburetor and the return line. When I turned on the pump I got between 3-1/4 and 3-1/2 pounds of pressure.

 

The original mechanical pumps are supposed to be between 3-1/2 and 5 pounds.  I thought that is a little on the light side, but once the generator is going, I guess the voltage will come up a bit and it will probably top 3-1/2 pounds.

 

I then did a flow test.  I put a graduated pale in the engine pay and ran the pump for one minute.  I got 3 Pints.

 

This is where things get odd.  The pumps according to Carter are supposed to put out between 6 to 8 PSI and up to 72 GPH.  That would be 9.6 Pints a minute. 

 

I called Carter and got a lot of double talk.

 

I hit my 1957 Carter Master book which is 5 inches thick.  In the back they have both the old Carter mechanical fuel pumps and the older larger vane electric fuel pumps.

 

In the section on the mechanical pumps they show how to test them.  They show their mechanical pumps, like the MOPAR manual, as having between 3-1/2 and 5 PSI.  They also show that the mechanical pumps are supposed to:

 

"Volume: One quart {2 pints} of fuel in one minute or less at 500 RPM"

 

In the section in the book on Testing, Removing, and Overhauling the older style electric Carter fuel pumps, it states:

 

"If the fuel pressure gauge is not less than the following the pump is satisfactory:

3 Pounds for a 24 Volt Pump.

2-1/2 Pounds for a 12 Volt Pump.

1-3/4 Pounds for a 6 Volt Pump."

 

 

If I use the old original Carter specifications, my newer style vane pump is just fine. I have 3.25 PSI and 3 Pints a minute.

 

 

When I talked with the people at the service center, they just mouth the 6 to 8 PSI and 72 GPH song.  When I asked for a PSI chart via voltage they tell me they do not have one.  I ask that surely the 6 volt, 12 volt, 24 volt versions have different outputs.  Nope, they are all the same I am told.  When I ask what the minimum volume output is they tell me they do not know.  I ask them how then will they determine if a pump is defective if they do not know what to measure.  They don't know.

 

Now, I purchased the pump via Amazon about a year and a half ago when restoring the '49.  About three weeks ago, since it looked like the fuel system was working ok, I purchased another pump to have a spare on the road with me.  I got this one via my local speed shop and the local warehouse. 

 

I took that unit out of the box and put 18" of rubber hose on it.  I took 3 feet of #12 wire and connected it.  I stuck the fuel gauge on the output of the pump. I put the end of the hose in the pale with the 3 pints of gas I took from the car test.  I turned it on.  Guess what, 3 PSI.

 

It is obvious to me that the published specifications are garbage. From Carter to American Car and Foundry (ACF) to Federal-Mogul to now some outfit named Castle Automotive.  I think over the years that the original specifications have been lost at the service end of things and all that is quoted is the ones for the 24 volt version.

 

I called back later and talk to another person.  I explain what is going on. I asked for them to call up the food chain and confirm the minimum and maximum design parameters for pressure and flow for the six volt pumps. I am waiting on a response.

 

I very much doubt that 2 pumps via 2 distribution channels a year apart are both "failing" in exactly the same way output pressure wise. 

 

If anyone has any thoughts, other then toss it and put the mechanical pump back in :-), or any experience actually testing for pressure and volume on fuel pumps for the flathead engines, please chime in.

 

Best, James

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I guess if your car was running well you would not be questioning the fuel pump output. Perhaps the car problem is not the electric fuel pumps fault and it is not a fuel issue. If you tested the fuel pump on your car and not on a bench, that may be why your results are different than Carter. Is it possible your fuel line has some restrictions in it?

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In the carter pump that you are using how old is the pump.  I had an old style rotary 6v pump on my 39 Desoto and the new fuel killed the diaphram.  I replaced this with an Airtex 6v pump that goes on the fuel line near the gas tank.  Most electric fuel pump are NOT designed to be a Puller style like a mechanical FP that we have on the cars.  So they need to be at the fuel tank to push the fuel.

 

This might be your issue.  Look at the instructions to see if they indicate that it should be setup as a pusher pump and not a puller pump.  Locatin might be the issue.  If this is an older pump I would consider chnaging over to the Airtex pump. cost around 48-55 dol;ars on the Bay.

 

Rich Hartung

desoto1939@aol.com

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Hi all,

 

I was testing the fuel pump more out of curiosity than anything else.  Just to rule it out.  I put on another carb I have which I rebuilt a while back and it started fine.  I cannot road test until they finish the construction on the street in from of my place.

 

The pumps are all new.  The one in the car is a year and a half old and has 1000 miles on it.  The one on the bench is new out of the box purchased last month. 

 

 

The rotary vane pumps are real pumps with an impeller.  No diaphragm to go bad.

 

The testing procedure I used is as specified in the carter literature.

 

I left a message at Carter HQ asking to talk with someone that actually knows what the 6 volt pump specs are.  We shall see if they call back.

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Hi James;

I too have one of these pumps installed in my truck. It is mounted at the tank but I did not fit any sort of bypass. I did fit a Holley fuel pressure regulator ahead of the fuel filter and carb. The regulator is set at 3.5#. I have never measured the flow but it seemed more than adequate. 3 pints a minute if you think about it is probably 4 or more times what your engine could ever use under the heaviest load.

 

Jeff

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Block off your return line and recheck pressure - motor off, ign. on, and then recheck fuel flow per min. as before. Flow GPH is measured with no resistence. No return line.

Pressure is the resistance to flow therefore No return line.

 

Doug

Edited by DJ194950
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Hi Guys,

 

The on car pressure test was without the return line....

 

The plot thickens.  I thought that it was due to some stuff in the carb and perhaps a float sticking.  I stuck another carb on it, same type also rebuilt by me, and took it out for a ride.  Same thing happened after about 15-20 minutes of running.

 

Got the car home and pulled the sending unit and looked into the tank.  Looked fine. I hate those big fixed round pickup screens as you cannot see the actual screen on these.  In any event, I pulled the Fram HP1 gas filter so I could shoot air back into the tank.  The filter is just ahead of the pump about 2-3 feet from the tank on the inside frame rail.

 

When I pulled the filter out of the housing boy was I surprised.  A lot of gunk in the bottom.  Now keep in mind that the tank was acid dipped and then lined by the same guy that has been doing my tanks since the 1970's. 

 

We put the filter in a pan and poured fresh gas over and through it and a lot of crap cam out. Including some fine glass bead.  Now this tank had sat in this car untouched since 1966.  Only the diesel fuel that was put in to pickle it. When we got it back it looked great.  I am wondering if one of the workers at the shop hit it with some glass bead to "help it along" before putting it into the acid tank.  I am also wondering if the pick up disc and line in the tank had some junk in it as well that did not clean out.

 

A 1000 miles of driving with fuel with alcohol in it may have "cleaned" it out and it all washed into the filter.  I suspect that the pump may not be able to keep up under running conditions.  An obstructions on the suction side is much harder on a pump than on the pressure side.  Perhaps the pump was getting warm and dropping volume just enough so that after the car warmed up when I needed more power that was it. 

 

On the way back after it acted up and I let it sit for an hour, I could induce the cut out by going high RPM in 3rd gear.  It felt like someone just squeezed the fuel line.  If I let up as soon as I noticed it, it would not stall and I could drive along fine at a slower RPM.  We also changed to a spare coil before the return trip.

 

I ordered a few of the filers, I used the last one on the '47 last week that I had on the shelf, and will try it again mid week once they come in. 

 

If that solves the problem, boy and I going to have a talk with the shop that did the tank!

 

James

Edited by James_Douglas
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Hi Guys,

 

I just got a call from the support people at Federal-Mogul.  They are supporting the Carter products for six more months and that is it for them.  The new group that purchased Carter...who knows.

 

Apparently and to his surprise is that the published data (which Speedway, Jegs, and all the rest use) of Up to 73 Gallons an Hour and 6 PSI are all "Free Flow" numbers.  Worthless to measure for car guys. The support man said that the engineer told him that...

 

The 6 Volt Carter pumps with a fuel pressure gauge stuck on the output of the pump is 2 to 3 PSI.  The volume is 25-30 GPH or 3.3 to 4 pints per minute.

 

I got 3.25 PSI at the carburetor and a little less than 3.0 pints in a minute.  With a fresh filter, one without junk in it, I will see what I get.  It looks like however that the pump is fine.  I was correct that the specifications were odd and misleading.

 

James

Edited by James_Douglas
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Jeff,

 

The margin may not be as much as one would think.  The main metering jets are about 320 CC/minute or about 0.70 Pints a minute.  I have the step up jet hole size (0.0413) but not the flow rate.  It is big, close to 1/2 the main jet size.  So assume another 0.35 for sake of argument.  Then add in the accelerator pump stroke coming out of the fuel bowl.

 

If you take off and hold it open you are using something on the order of 1.0 to 1.5 pints a minute.  I could get three pints plus or minus a little bit.  In theory, it is fine.  But if anything causes an issue, like a slightly clogged filter, a kink in a line or some such and I can see where a problem could develop.

 

It will be interesting to see how it runs after I get the new filters.

 

James

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James;

You are right of course. Any obstructions or blockage and the flow rate could be quite a bit less. This is certainly a good case for maintaining the entire fuel system to a very high standard. It isn't just the age of our vehicles though that makes this important. Every time you fill up you run the very real risk of introducing all sorts of contaminants to the system. I have just seen too much of this. I have added a couple of large modern filter elements to my truck and plan on changing them often.

 

Jeff

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One of the problem areas with putting a coating in these cars fuel tanks can be the hidden floating pick up with a screen can get blocked by the coating. Leave it upright to dry and it will stuck in the coating and maybe plug the pickup screen. Leave it upside down and fill the tube of the pickup with coating?. Rotating the tank regularly as it drys seem to help or put a low pressure flow of compressed air thru the tube as it drys.

The sealer I've used twice drys too slow and it seems to make it difficult to do either.

 

Seems that you have good luck with however your tank repair guys have done in the past but no one is perfect.

 

 Both on my reseal tank jobs had problem with fuel flow because of partial fuel tube or pickup problems and required a good amount of air pressure applied to the output fuel fitting (gas tank cap off!) to not pressurize the tank just the pickup part! It did at POP (which it believe was the blocked screen being blow loose) and after that had a good free flow of air into the tank and upon retest of fuel flow was good. If you have good airflow at low air pressure then that,s not your problem area, but if not:

 

Not too hard to check this at the tank. Will most likely need to test by putting a section of hose onto the tank fitting and put hose lower than fuel level and siphon the fuel  to get flow started and measure, it should have a good free flow.

 

Stuff happens.

 

Best,

 

DJ

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To close the loop on this thread...

 

I got the new fuel filters to day for the Fram HP1.  I put the filter in and took it for a ride.  I could not get it to cutout/die.  I ran the car up in 3rd gear and held it at an uncomfortable RPM.  Boy, do these things make noise when held at high RPM.  It just screamed away.

 

The outside air temperature was much cooler the last few days and there is always the chance that it is somehow heat/resistance related, but I doubt it.

 

I will run it hard over the next week and lets hope that is it.  I will carry a spare filter in the trunk from now on!

 

Even though it was a pain in the ass, I learned at least what the vane carter pumps really put out as part of this process.

 

Thanks all, James

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  • 3 weeks later...

Well,

 

Guess what?  It did NOT solve the problem.  Over the last couple of weeks I have been test driving the car and the problem is back.  It seems to take an hour or so of driving for it to happen.  Here is what has been done.

 

1. Replaced carburetor with a different one.

2. Replaced spark plugs.

3. Replaced condenser & check inside of dizzy.

4. Took off Carter Electric Pump and replaced it with a new mechanical engine driven pump.

5. Changed fuel filter.

6. Took out gas tank and used my mercury outboard (restored) tank.

7. Checked every nut and bolt on the engine that could be vacuum related.

8. Replaced the coil.

9. Checked to make sure we have 6 volts at the coil.

 

The other day we drove the car north out of San Francisco on the US 101.  We went to Geyserville some 75 miles north.  We then cut up to Calistoga and then over a mountain with steep uphill grades back to Santa Rosa, CA. This included 70 MPH freeway, back 2 lane curvy roads and steep hills.

 

The car ran just great for the entire two hours.  Then we shut it down in Santa Rosa for about 20 minutes, a pee break, and took off again. 

 

Not 10 minutes after we took off the car started to sputter and cut out on any kind of hard acceleration (load).  If I took off real slow and easy I could keep going.  On level ground if I took it easy it ran ok.  Trying to go up any grade or small raise that required leaning into the throttle and it would start to cut out.

 

It did this off and on all the way to San Francisco.  We had to stop multiple times for 20-40 minutes.  We nursed it down back roads and avoided steep hills and then went through Sausalito and up the back way to the GG Bridge as I could use 1st-2nd gear. It sputtered but made it.  Once on flat level ground with light throttle we cruised across the bridge and back home. 

 

 

I have talked to all my car friends here in SF as well as a couple of professionals that work primarily on classic cars. We are all scratching our heads.

 

I have a short list of a couple of other things to try based on conversations.  They are:

 

A. Open up the valve clearances in case when they get real hot and heat soak they are being held open and causing a power loss...

 

B. Replace the disc brake vacuum can check valve in case it is failing and allows the vacuum can to "suck" on the intake manifold under a load which would cause the carburetor step up piston to pull down and cut off fuel (remember the 1947 problem thread)

 

C. I have a couple of new, but not replaced fuel hoses that I want to replace just in the chance that there is an internal problem that I cannot see.

 

D.  I will change the Taylor spark plug cables with new/other ones.  I am using them on the big '47 Desoto and have been for 10 years without any issue.  But, you never know.

 

 

Does anyone have any other ideas?  One thought is that somehow, and I do not know how that would be, that the Tip-Toe-Shift (M6) interrupter switch is causing the coil to be shorted...but, at light throttle I do not see how that could happen.

 

I am taking the day off and going to go look at a '63 Chrysler...

 

Best, James

Edited by James_Douglas
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Have you blown back the fuel line from the pump to the tank??? I had a fuel flow problem a couple year back.  I took the fuel pump apart (mine does not have the glass bowl on the bottom)  the hollow bolt that retains the bottom chamber in place and allows fuel to flow to the upper chamber had a piece of crud it in.  It acted like a one way valve sometimes and would allow gas to pass with no problem, then if it changed position within the body of the bolt it would restrict the flow, Drove me crazy for a couple of months .  Car would run great, then wouldn't run, then, run great.  Don;t know what it was or how it got in there, but once I cleared it out fuel issues went away.  Also this pump had a brass screen at the top of this chamber that was half covered in rust from my original tank.  

 

 

Are you pumping through the original pump or have you bypassed it?  I guess if you bypassed this above is moot.  I always wondered about the efficaxy of coating a tank when there was the sintered brass filter on the pickup.  How does the coating not get on to the porous pickup and not cause problems?

Edited by greg g
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Hi James;

Sure sounds like it may be heat related. I have a couple ideas to help diagnose the problem. You might want to consider hooking up a few extra instruments where you can see them while you are out on the road. First a vacuum gauge. A decent gauge should give you and indication of how well your valves are working......and any vacuum leak that may occur. Second item would be a remote fuel pressure gauge. This could be useful to note if there are any significant changes in fuel supply. The last item would be a good Volt gauge. Sometimes an intermittent electrical issue can be spotted by small fluctuations in voltage readings.

This array could all be hooked up temporarily and in full view of the driver and/or a co-pilot. Fwiw I am of the opinion that a vacuum gauge is a good full time accessory in pretty much any older car or truck. They are a great monitoring device.

 

Hope this is of some help.

Jeff

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Hi Guys,

 

I have given myself a few days of not working on the '49 to clear my head.  I will pick it up again on Sunday or Monday.

 

The fuel lines have all been blown with 90 PSI air several times...

 

The one thing I did today, since it is warm here, no fog, on the coast side of SF is to hook up the water hose to the fuel line fitting in the gas tank.  It is out of the car.  I then opened it up full blast and looked inside.  It appears to be flowing ok even though I cannot see the bottom of the pick up.  Given I still have the problem with the Mercury outboard tank in the car...I think I do not need to open up my and play with my original gas tank.

 

 

The suggestions on hooking up some gauges is a good one.  If after I do everything else it still does it...I will add gauges and see what I can see.

 

One interesting thing.  In the 1949 Desoto Service manual it has a " SERVICE DIAGNOSIS" section.  The 4th item in the list under "ENGINE STALLS" is Insufficient Valve Clearance. 

 

In a few days I will do everything and let you guys know how it goes.

 

James

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James, I had a problem with my snow blower engine last winter.  It would only start by spinning it on the electric start, no amount of rope pulling would effect it.  When it ran it had little power and was blowing blue flame out the exhaust, and also backfiring under load. A compression check showed 35 psi ,I pulled the head and found the exhaust valve was not fully closing.  This engine does not have any adjustment for valve lash and the end of the valve rides cam with no tappet or lifter.  I still have no idea of how the valve lost its clearance, whether the seat eroded, or the stem stretched or what.  Any way, I removed the valve and ground off the cam end enough to recreate enough lash to allow the valve to fully close, and trimmed the intake valve a bit also as while that valve closed, there was less clearance than I could measure with my feeler gauge.  I believe I did both of them to have.008 gap.  Head back on compression at 80 psi, started easily, runs good, and backfiring and blue flame gone.  

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Hi Guys,

 

I have not done anything on my punch list yet on this problem...but, I did decide to cut a 3" hole directly below the gas tank pick up since the tank is out.

 

We know it is not THE problem, as if you remember I tested it with my old restored mercury outboard tank and the problem came back.

 

But, if there is any restriction at high demand it is possible that the engine leaned out a bit and that would cause a lean condition which even if not enough to cause the kind of problems I had with the '47 Desoto it would increase exhaust gas temps.  That in turn could cause an issue if a couple of valves are too tight.

 

The inside of the tank with the round can pickup (the tube comes in of the side of this can) has a sintered brass filter.  This thing was not only clogged with years of use, it had tank sealant on it.  So I removed it.  I will clean is all up and weld a round patch on the bottom.

 

So much fun.

 

James

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I have had problems with a CJ tank that was coated in the past.  At high demand there was a "flap" of the coating that would get into the output and restrict flow.  The motor would stumble and then recover as the bowl filled back up.  When gas was needed again it would do the same thing.  I could never figure out what was going on as it was good at idle and just gave up replacing the tank one day.

 

I'm not saying I have a solution, just had a similar problem in the past...

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Hi Guys,

 

I have not done anything on my punch list yet on this problem...but, I did decide to cut a 3" hole directly below the gas tank pick up since the tank is out.

 

We know it is not THE problem, as if you remember I tested it with my old restored mercury outboard tank and the problem came back.

 

But, if there is any restriction at high demand it is possible that the engine leaned out a bit and that would cause a lean condition which even if not enough to cause the kind of problems I had with the '47 Desoto it would increase exhaust gas temps.  That in turn could cause an issue if a couple of valves are too tight.

 

The inside of the tank with the round can pickup (the tube comes in of the side of this can) has a sintered brass filter.  This thing was not only clogged with years of use, it had tank sealant on it.  So I removed it.  I will clean is all up and weld a round patch on the bottom.

 

So much fun.

 

James

James;

I do love a good mystery.......although it is too bad you are having to go through this.

From everything you have posted about this problem it sure sounds like the root of it is heat related. My guess is that it could be something very difficult to spot......like a small crack in the intake manifold or a part that warps or distorts when it reach's a certain temperature. Honestly I hope it is the valve adjustment for your sake......as these other things can be extremely difficult to pinpoint. This is why I suggested hooking up a vacuum gauge. A sudden or even slow drop in vacuum when running at a constant speed could confirm this theory.

 

Keep us posted as I am very curious about what you find out.

 

Jeff

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Working on the punch list on this problem.  One thing I decided to do was to cut open the bottom of the tank.  Although it is not the problem, it may have contributed.  I am glad I did as you can see in the photo.

 

The 1949 tank, I can not talk about my 1947 tank as I tossed it and had a stainless on made up, uses a 3 inch sintered bronze filter.  It was 80% clogged up.  If this restricted fuel flow, not enough to starve the engine, but to cause it to lean out at high load, that would drive exhaust gas temperatures up which, if it is a valve growth issue, would not help.

 

{What a run on...you would think I never went to school!}

 

In any event, thought people may like to see the actual pick up in the tank.

 

Best, James

post-60-0-55705300-1403879714_thumb.jpg

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Just curious. Have you ever replaced the ignition lead from the coil to the points? That will give you the same symptoms.

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