The fuel pump for the Willys F-head engine is mounted on the left side of the engine block and is mechanically operated by an eccentric on the camshaft. According to the Jeep Universal Service Manual, "The double-action fuel pump resembles two single-action pumps placed one above the other. A single fuel pump rocker arm actuates the two separate diaphragms. One diaphragm is part of the fuel delivery pump...the other diaphragm is part of the vacuum pump. The fuel pump consists of a metal body, a rubber diaphragm, rocker arm, valves, springs, gaskets, and a glass sediment bowl complete with strainer."
Jeff inquired on The CJ-3B Bulletin Board: "I have just made a change to an electric fuel pump from the mechanical one. I was trying to get my engine running and I finally found the problem in the carburetor -- it wasn't the pump. But why should I stay with the mechanical rather than the electric fuel pump?"
Wes K responded: "Perhaps the real question should be 'Why stay with the electric pump?' The majority of the electric fuel pumps in low performance vehicles got there for the same reason yours did. The owners were unable to properly troubleshoot their fuel systems and started throwing parts at it. The next best reason for installing an electric pump is in an engine swap where there is no room for the mechanical pump any more.
"The CJ-3B performed to its original specs just fine with the mechanical pump (left). The electric pump usually requires a pressure regulator so its output pressure can be matched to the input specs of the carb. The electric pump for safety reasons should have a kill switch (usually a simple oil pressure operated switch, but often an impact switch) which will turn the pump off if the engine quits or when you have a collision. Some electric pumps require a return line be added from the pump to the tank. Electric pumps should have a filter between them and the tank to protect them from sediment and other old rusty objects.
"I think it's easy to see that the original mechanical pump is the simplest installation and easiest to use."
Jeff: "It seems most Jeepers prefer the mechanical pump over the electric because it would give the carb the required amount of gas, as in not too much. My engine is backfiring some, especialy when I shut it off. Would the electric pump be the cause of this -- too much gas? If it is, how would I slow the pump? Or should I go back to mechanical and see if it works?"
Brian Hurt: "Most electric pumps put out more fuel than required by the carb. The one I had on my CJ-5 was cheap and worked fine. I swapped back to the mechanical pump because I have charging issues with the generator, and I was worried one trail ride that I wouldn't have the juice to keep the electric pump running. No battery, no electric pump = no gas pumped to the engine. It's just one less electrical thing to go wrong. And also, the cheap pumps do go bad. They just die. If your mechanical pump still works, hook it back up and keep the electric as a back up. If you stay with the electric pump I would suggest a fuel regulator after the pump, before the carb. Also, I never ran a filter before the pump. Anything big enough to cause damage to the pump won't fit down the fuel line. But don't hold me to that!"
Jim Hubbard: "I have had issues with electric pumps on several occasions. If while working on your Jeep you inadvertently leave the key on, the pump could and probally will fill your enging full of gas (called 'hydrostatic lock'). I have seen several fires caused by a needle valve sticking open and an electric pump continually feeding fuel to the fire. Failure is common with electric pumps, and if equipped with necessary safety switches, that compounds the problem. I just put a new pump on my 3B and from O-Reilly it was $54.00 with the vacuum pump. Be safe man, use the mechanical pump; when the engine dies the pump quits."
Eddie Stephens: "This is correct about the electric fuel pump flooding the engine -- been there, done that. I just purchased a CJ-3B with electric pump, and it will be the first thing to go."
Ed Wilson wrote: "After a complete engine overhaul, carb rebuild, and addition of electronic ignition, I am still having difficult cold starts. An electric fuel pump was one remedy suggested. However, one advisor says the two pumps would work together, possibly using the electric unit only for startups, and one says I should bypass the mechanical pump.
"Also, a non-return valve in the fuel line was mentioned as a solution. I have not inspected the fuel pump yet, as it seems to work fine otherwise."
H. Woolridge: "You mentioned cold starts were a problem. Is the engine flooding? I had this problem with mine and an in-line fuel regulator from NAPA helped."
Brent: "I put an electric one on my M38 and have had good luck with it. I placed it inline, still through the mechanical pump. I bought a low pressure pump from the parts store -- it doesn't have a return line. The only problem is that it is a little loud."
Jon Hardgrove: "Have you checked to make sure the carb has no fuel (main reason for electric pump) when doing a cold start? Next time you do a cold start, remove the air cleaner, put on a set of goggles, manually open the choke, and work the throttle linkage to determine if the accelerator pump squirts a squirt of gas into the throttle area. If yes, electric pump probably not the answer. If no, start the engine (you now know there is gasoline in the carburetor), stop the engine and repeat the test. You now know if the accelerator pump is functional. If an electric pump is installed, remember 'big brother' wishes you to wire it from an oil pressure switch (safety), and to acquire a pump with approximately same pressure as an O.E. mechanical pump. Also, electric pumps are 'pushers'. The pump should be located as close to fuel tank as possible."
R. Jack: "My Jeep came to me with an electric fuel pump and fuel pressure regulator installed. I removed it and placed an original type pump. But my problem was rust in the gas tank. The tank outlet had no strainer, allowing a very small lump of rust to restrict the fuel line which was all visible when I cut open the gas tank before junking it. Additionally, check those GI jerry cans for rust in the bottom seam. Most were bad when surplussed."
Jax: "I remember some info on an inline fuel filter that could screw in right into the carb fuel line inlet. I think it was a Fram but forgot the part number -- does anybody remember?"
Doc: "One of the first things I did after buying my Jeep was to get rid of a jury-rigged piece of copper tubing that ran from the fuel pump to the carb. Copper tubing will become brittle from vibration, leading to a dangerous situation from leaks. While I had the line off, one thing led to another and I rebuilt the carb.
"During the rebuild, I found lots of crud in the float bowl. I even found my nemesis, little specks of blue silicone gasket maker. I got to looking at the fuel filter screen inside the fuel pump and realized it couldn't catch the small stuff. While trying to find a fitting to plumb into the carb inlet fitting, I had a brainstorm.
"A Fram G3596 fuel filter (right) threaded right into the carb inlet. I happened to have one lying around since it also fits my F250 truck. The other side of the filter has a 5/16" flare fitting for which I formed a new piece of steel tubing to run to the fuel pump. This filter now catches most anything that gets past the coarse screen in the fuel pump. Whenever the filter is changed, cut the old one open with a tubing cutter. You'll be amazed to see what it will catch.
"The 5/16" line to match the filter is not the stock size. I had to change the output elbow fitting on the fuel pump to match."
Randy: "As I disassembled the engine in my 3B while rebuilding the Jeep, I discovered a spacer between the fuel pump and the engine block. This spacer appeared to be original to the Jeep and as I cleaned the spacer I discovered a W-O part number on the spacer. Recently my new fuel pump has failed and I am in need of replacing it again.
"The question is, why was this spacer originally installed between the fuel pump and engine block and is it needed? I can find no documentation to indicate a difference in the length of the actuating arm (23, right) on the fuel pumps. Could this spacer have been installed to decrease the pressure applied to the camshaft eccentric, or possibly used to extend the life of the pump by allowing the removal of the spacer after considerable wear on the actuating arm, thus allowing the arm to be placed deeper on the eccentric?"
Todd Marquart: "You are correct. The spacer is designed to lower the fuel pressure. I bought a new fuel pump and it overflowed the carb when installed. I purchased 2 of these spacers and used one. The folks I bought the spacers from asked why I didn't just add a pressure regulator, and I stated I wanted it to be original and simple."
Bob: "I was always under the impression that these spacers were used on military Jeeps, but the theory that they were meant to reduce pressure sounds more logical to me. I should put one of these in."
Todd Marquart: "I have an M170 with the military fuel pump and spacer. I believe the spacer on the military Jeep is required to make the pump fit correctly. The military spacer is very thick when compared to the 1-2mm thick spacer for pressure regulation."
Jax: "I'm changing to a single action diaphragm fuel pump. On my old one (dual diaphram with vacuum) there was a metal spacer in addition to the gasket. I'm wondering if the spacer is necessary with the single action fuel pump?"
Ross: "I just fitted a new single action pump and you remove the spacer to fit them. Apparently the same as a CJ-2A -- no spacer."
Scott Blystone: "Since I've not seen this info elsewhere, here goes: To replace the fuel line from the tank to the fuel pump you need to go to virtually any parts store (NAPA, Advance, PEP boys etc) and buy the premade 60-inch 1/4" diam. steel fuel line. Every store I have been in has these premade.
"This is a great project - takes only 20 minutes or so and only costs a few bucks. On my CJ this was easier than changing a light bulb. I had to change the line because I damaged the nut gettting the old one back on after tank removal."
Don Norris took photos of his new fuel line. The first shot (left) shows the fuel tank connection and the clip on the hat channel.
The second photo shows the line passing through the toe board brace (120K JPEG).
The third photo shows the line strapped to the fender and bending toward the fuel pump (120K JPEG).
JC Jenkins adds: "When I replaced my fuel line, the first thing I did was to install a quality brass shut-off valve, so I could shut the gas off, if I ever wanted to remove the tank, and it serves as a cheap anti-theft device (turn it off, they won't go far). Also I have an in-line fuel filter right below the valve (we change the filter every year, this makes it easy), then we ran a fitting for 3/8-inch rubber fuel line (holds more gas, therefore stays cooler, less vapor lock in the rocks). I hope this helps: I know it isn't exactly 'stock', but it really works for us."
Jim Sammons comments: "The fuel line fitting coming out of the tank is 1/4-inch NPT. You can buy a fitting which has a 3/8-inch hose barb on the other end to run hose. However here in south Texas the brush has a habit of trying to remove the hose from under the tank when hunting, so I replaced the whole mess with 3/8-inch stainless tubing. The stuff is easy for me to come by since we use a lot of it in the oilfield. I ran it all the way to the fuel pump with an in line filter just before the pump. Be sure no matter what you use you wrap the threads with teflon tape which will seal the threads and make for easy removal if necessary."
Alan Haley: "My fuel line from the pump to the carb was a 3/16" tube that greatly resembled (and which I replaced with) a brake line. It runs from the pump, across the front of the engine just over the main shaft pulley, bends to follow the block back just under the oil filter and then immediately up. Bends once again over the top of the block and then back upon itself to connect with the carb. (See also Eric Lawson's photos in Engine Rebuild, Page 8 on The CJ3B Page.) I made mine up a lot faster than it took to actually get it installed. I would suggest you take 10 dollars and buy a tubing bender to do this. You can get them at most auto supply stores.
"I had a huge amount of trouble getting the Jeep running this spring and spent a good amount of time on the fuel supply side of the engine. Some people said that running the line this close to the engine would cause the fuel to heat and interfere with pumping. I am positive that this course of travel was the original design and once I solved the real problems that I had (weak fuel pump and gas tank debris) the fuel supply was no problem. I would recommend that you install an easy-to-get-to inline filter."
Scott Blystone: "If there's no gas getting to the carburetor, there are two ways to approach it depending on how anxious you are to hear your CJ run:
If you have the original pump (glass on top, vacuum lines) there are no rebuild kits available but you can still remove it and clean out gas passages, check for broken return spring on actuating lever, etc. If you cannot solve fuel pump problem, buy a new one - under $40 from numerous suppliers. Will not be original glass top but still has vacuum assist ports. It is possible that the fuel filter is so badly clogged as to not let gas pass through but I doubt it. You can take it out entirely for a few minutes without worry. Not a tough repair but a smelly one. My wife hates it when I come in from the barn smelling of gas."
Note: For seals and parts for rebuilding a fuel pump, try the Antique Auto Parts Cellar.
Thanks to Scott and the other contributors. The illustrations of the fuel system and the exploded pump come from the 1956 CJ-3B Parts List, and the F-head picture is from Facts about the Universal Jeep for Service Stations (and other Willys brochures.) -- Derek Redmond
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