Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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#481953 05/23/23 02:17 PM
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Mike Z Offline OP
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Today on the way home, driving my 1939 Master Deluxe 2 door, driving 45 Mph, all was going fine, then the engine started to buck as if it was running out of fuel. I slowed to 40 Mph and it smoothed out. Then later it happened again at 40 Mph, again I slowed to 35 Mph and it smoothed out. Happened once more and smoothed out at a slower speed. I suspect fuel delivery of my fuel pump. Does anyone know what the fuel pressure, vacuum side vacuum and fuel delivery of this pump is? I appreciate the help, Mike

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Mike Z #481955 05/23/23 03:02 PM
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One quick check is to disconnect the fuel line at the carburetor and crank the engine while you watch the fuel discharge. I cannot find a spec for the delivery rate.

The pressure should be in the 3 - 4 psi range. Much more and it will flood the carburetor. The tricky part is that you can have pressure but no flow.

I would also check for a restriction in the line going to the pump.


Rusty

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Mike Z #481965 05/23/23 06:58 PM
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Well.... I thought I posted a reply, but for some reason it didn't take. I set up to measure the pump pressure and found that it was 5 pounds. My 1942 Motors Manual say 3 pounds is max. My son the Buick mechanic came over and helped out. I have a seciement bulb at the carburetor and we could see a few rust particles in it, but not much. We then did a flow test. I ran the engine until the carb went dry and I only got about 1/3 cup of fuel. I'm pretty sure that is not enough. So we removed the fuel pump and found the filter on top of the pump had a LOT of rust particles in it. Maybe 1/2 teaspoon. I have a vacuum bottle and pulled on the gas tank from the input of the fuel pump and the first pint of fuel was dirty. The second pint was nice and clean. So tomorrow I want to try and clean the pump and maybe it is OK, other wise I think I'll get a new one. Let you know. Thanks, Mike

Mike Z #481967 05/23/23 07:16 PM
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Good troubleshooting technique. Your results are not unusual with these classic cars. I installed a Fram G2 filter at the tank outlet on my ‘37. It stopped the crud coming from the tank.

I did not have a filter between the pump and the carburetor. It was an old style pump with the glass bowl and screen.

While I have never tested it there have been other posts that recommend you not use multiple filters due to the increased restriction.


Rusty

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Mike Z #481977 05/24/23 08:33 AM
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Mike Z Offline OP
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In the past I never had any high speed trouble, even with both so called filters. Actually, the fuel pump is an AC mechanical type AF pump. It has the glass bowl on top of the pump with a rock type filter element. The sediment bulb between the pump and the carburetor is a Carter sediment bulb from my old 1958 Chrysler Imperial and has the same type rock element in it. Later today I want to try and clean out the pump. Thanks for the help, Mike

Mike Z #481984 05/24/23 02:51 PM
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This morning, and I mean all morning, I reinstalled the fuel pump. I had forgotten how difficult it was to start and tighten those TWO bolts. Anyway it's back in the car. I want to wait until my son can help me with the fuel delivery test, but I think I have another problem. I can see bubbles in the input of the fuel pump. You can see them thru the glass filter bulb. The inlet goes to a little stack and I bet that 1/2 of the inlet flow is air. After looking at the pump the only place where air can be pulled into the line is at the inlet pump connection and the gas tank connection (or the line has a pin hole, but I could not see and evidence of that). I believe that both connections are sealed, so that leaves the tank. I'm wondering if the pick up pipe may have rusted to the point that there is a pin hole that is in the air of the tank. Currently, I have less than 1/2 tank of gas. Suppose I can fill the tank up and see if the bubbles go away. Geezzzz...... it's always something, Mike

Mike Z #482005 05/25/23 10:42 AM
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When I was at the point to make a decision to keep or replace my tank I bought a cheep camera to look inside the tank. Worked great cost about $30 on Amazon. Just put it down the filler neck and took a good look at everything. 5 minutes of looking around in there made my decision to replace the tank. Since that time I have used it to look into walls, cylinders and many tight places that would have required disassembly to get at before. Nice tool to have in the box.

Do you have steel fuel lines? If so it could be rusting from the inside out. I had that happen on an 04 Chevy truck.

I run a filter prior to the fuel pump. It is a glass inline one and while I have seen a few bits of stuff in it nothing major on mine. Just installed a inline one that looks like what should have been there prior to the carb. Have not had any issues running two on my car. Then again I have only had two on it for a couple weeks.


I have found that having an old car is a constant project that is never done. I think that is a good thing. Keeps me learning new things. Having two from different eras is just a form of higher education.
Mike Z #482070 05/27/23 09:07 AM
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Say that's a good idea! I'll see what I can find. I filled the tank and the bubbles did not go away. Next I dripped oil on both pipe connectors. The connector at the suction side of the pump was the bubble problem. But that didn't fix the low fuel flow. I found some information stating that 25 seconds of engine cranking should deliver about a pint of fuel (16oz), my pump only delivers about 2 oz. So I called Chevy's of the 40's for a new pump.They do not have any and do not expect to get any until after September. I called the Filling Station and they also did not have any. A few more calls and still no soap. I did find a rebuild kit. Hopefully that will solve this problem. Let you know how the rebuild goes, once I get it and what pressure and fuel flow I get after the rebuild. Thanks, Mike

Mike Z #482080 05/27/23 03:46 PM
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Mike Z Offline OP
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Well, shock and surprise, the rebuild kit came in the morning mail. So I changed out the parts. The old inlet check valve was definitely leaking. Even with my OLD eyes I could see that the rubber had failed. One item, the new pivot pin for the lever arm was sloppy and I could push it out with my finger. I measured it and it was 0.004" smaller than the old pin. I used the old pin. Re mounted the pump on the engine and tried the fuel flow test. I got maybe 6 oz this time, where I had 3 0z last time. I think that it should be more. I'm wondering about the eccentric on the camshaft. Maybe the pump lever arm is not moving far enough. Does anyone know what the travel should be on the pump arm. Maybe tomorrow I can remove the pump 'again' and set up a dial gauge to measure the eccentric movement, Mike

Mike Z #482085 05/28/23 04:25 AM
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Did you hold the arm to pull the diaphram against the spring as you tightened the screws down, if this isnt done the diaphram has limited travel therefore limited fuel delivery.
Tony


1938 1/2 ton Hope to drive it before I retire
Mike Z #482088 05/28/23 09:06 AM
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Yup, I did. Done it before and my OLD brain remember it, amazing! Anyway I found that the travel on the fuel pump should be 1/4 inch. I'll try and measure it next week. In the mean time I want to clean out all the lines and the tank. Try and get the best situation I can, Mike

Mike Z #482105 05/28/23 03:04 PM
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Well.... today I had sometime to sneak away for long enough to drain the tank and blow out the lines. There was a little dirt, but not that much. I thought about removing the tank, but since I didn't see much dirt, I may not. While the tank was draining I had about 10 pounds of air on the outlet. I figured that maybe that would stir up anything in the tank and hopefully come out in the drainage. Mike

Mike Z #482170 05/30/23 12:44 PM
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This morning, despite the hot weather, I measured the travel on the eccentric of my camshaft. Using a dial gauge I measured nearly 0.300". I read somewhere that the travel should be around 0.250". That is a relief, saying the camshaft is OK. So with the rebuilt pump, I have good pressure at the carb ~4# (dead head) yet the flow is a little low maybe 6 oz in 20 seconds, maybe my reference is not right, I read 16oz in 30 seconds. The tank seems clean, the lines are open. I think bow is the time to reassemble the whole mess and try it out for a while. Thanks for the help.

Mike Z #482195 05/30/23 10:40 PM
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6 oz in 20 seconds is 18 oz per minute or a tad less than 17 gallons per hour. Since you didn't specify the engine rpm I assume at or near idle speed. Therefore the pump output is greater than the tank capacity I don't see it will likely be a problem.


How Sweet the roar of a Chevy four!
Mike Z #482200 05/31/23 04:51 AM
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Like Chipper I seriously doubt the car will use 17 Gallons an hour at wide open throttle which I suspect you will never experience unless you start racing the car. I suggest you start looking into the carburettor fuel passages for a restriction in the main fuel circuit.
Tony


1938 1/2 ton Hope to drive it before I retire
Mike Z #482289 06/02/23 12:02 PM
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I've driven the car around quite a bit and all seems OK. So I deem this problem solved. Thanks for the help, Mike


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