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The text following is part of a series of articles written by John S. Henry on the restoration and maintenance of air-cooled Volkswagens. While his experience is exclusively with the Beetle, many of the techniques can be applied to other models.

This text is copyrighted and duplication, re-distribution or publication is prohibited without consent of the author.

Article: The Fuel Path: Tank to Carb
Last updated: 10/27/01

The Fuel Path: Tank to Carb

Symptom: Your car just quit running and you suspect a fuel problem; you feel guilty that you really don't have any idea how the gas gets from the tank to the engine; you smell gas all of the time when you drive your Beetle.

It occurred to me reading the frequent fuel flow related posts in the rec.autos.makers.vw.aircooled newsgroup, that it might be a good idea to devote an article to "Fuel system restoration". I don't want to get into the carb, but all the stuff ahead of it can be a real mystery to the novice. Some quick text can really shed some light on this. So I will start at the tank and work my way back.

But first, a quick word in general, about gas. When gas sits for a very long time, it breaks down and forms a gummy, brown substance often referred to as "varnish". It will quickly gum up small moving parts like carb float valves. And this stuff has a strong stinky smell, nothing like fresh gas.  It is easily removed and/or washed out using a strong solvent like lacquer thinner or acetone. But be careful with these solvents. Acetone, in particular, will quickly eat paint and my break down certain types of rubber or gaskets.

And I want to mention clamps. The "screw" type are OK, as long as they are stainless steel (most are stamped as such if they are) and are not over tightened. But I don't think that they look as nice as the "spring" type. These are the ones that look like a circle with 2 "ears" and are made of a highly tempered steel. You squeeze the ears together with pliers to open the clamp, slide it over the hose and release. You can buy these at most good hardware stores, but make sure you get the right size. The clamp should just barely slip freely over the hose when opened all the way with pliers. Bring a piece of fuel line hose with you to store to be sure. Another nice thing about these kind is that you can't over tighten them and damage the rubber line like you can with the screw type

The Gas Tank

OK, first things first; the gas tank is in the front of the car. It makes up the "floor" of the trunk area. '55 to '61, the tank had a big "hump" going across the width of the car, and the cap was a large (about 4 inch) diameter on the passenger end of the hump. In 1961, the tank became flat on the top, making for a flat trunk space floor. Until 1967, the filler was via a neck protruding up on the front right corner of the tank with a cap on top. It required you to open the hood to fill, like the older versions. In 1968, the filler cap was accessible from outside the car, via flap on the upper front passenger side (right) quarter panel. There was an important "vent" line also from the top of the tank to the filler neck area in the front quarter. I'll have to plead ignorance about later changes, as I have no experience with 70s Beetles. The Supers had some other changes in this area.

The gas leaves the tank via a "drain" on its bottom. A short rubber fuel line connects the nipple on the bottom of the tank to the stub of the main fuel line on top of the tunnel in the front (take one of your front wheels off, and look in, beyond the inner quarter). Hose clamps must be used. A threaded collar holds the nipple to the bottom of the tank. Inside the tank, over the protruding pipe, is a thin, cylindrical mesh screen made of a fine copper screen. These are readily available new. You must remove the collar at the bottom of the tank and pull it out to access this screen.

Removal of the gas tank is quite simple. It is held in place by 4 bolts that clamp the tank to the body via metal brackets. (pull up the floor mat in your trunk, you will see them). If your rubber hose under the pipe is long enough, you may be able to remove the 4 bolts and tilt up the front of the tank enough to access the hose clamps and remove them. Otherwise, you must crawl under and remove them from below. A little tougher, but do-able. Take a front wheel off to do this.

The Gas Tank, Common Problems

Debris from decades of use can settle in the bottom and clog the screen. I had this happen in my first '68 once. The car would run fine until you got it out on the highway. After a few miles, it would just stop. In the time it took me to check out everything in the engine compartment, enough gas would trickle down, and when I tried to re-start it, it fired right up. Another few miles down the highway and it stopped cold again. I went nuts with this. I got it home and checked fuel flow from the pump. Of course, sitting in the driveway for a half hour or so, enough gas trickled down to show a steady pulse of gas from the pump. I rebuilt the carb and replaced the line filter in the engine compartment to no avail. Ultimately I removed the fitting on the bottom of the tank. As it turned out, my copper screen had completely rotted away and a small stick (yes, a piece of tree branch) about 3/16" in diameter had found its way down inside the pipe at the bottom and lodged there. It allowed enough fuel through, except to sustain a highway run. This happened the day before my big date to the "Journey" concert in 1981. I had to drive my mom's '76 Plymouth Valiant. (but it DID have A/C)

Another common problem is rusting out of the bottom of the tank. This happens because the pipe in the fitting sticks up (inside the copper screen) about 1.25" and never allows the last amount of fluid to totally drain from the tank. AND, water that forms inside the tank from condensation is heavier than gas, and therefore rests at the bottom and never gets drained away. BINGO! Rust. Rust=perforation=gas leak.

The Gas Tank, Recommended Restoration

If your tank bottom is rusted and slightly perforated, you may be able to repair it. I have used an ordinary propane torch and solder to seal up perforations. Remove the tank, grind the bottom outside down to shiny metal, heat the perforated metal with the torch and apply ordinary rosin core electrician's solder. Let it "pool" over the area before removing heat. If you have no experience with solder, you may want to "practice" first on some scrap metal. The basic concept of soldering is to heat the METAL to a temperature so that it will melt the solder; not heating the solder itself with the flame. You do not want to heat the metal so much that it is discolored. Wipe it down with a solvent like lacquer thinner to remove the excess rosin and wire brush it lightly and either paint it or apply roof tar (see "Rust" article).

Did I mention that gas is highly flammable? Actually, gas by itself, is not. The FUMES that gas forms when it evaporates are highly flammable. Just draining your tank good is not nearly enough to approach it with a torch without a death wish. Remove the tank from the car, open the filler neck, remove the fitting at the bottom. Then use compressed air or a COLD hair dryer to blow out the tank. You should not even be able to smell gas before it is safe to torch. Another method is to fill up the tank with water to chase out the vapors, then empty it. The heat from the torch may dry out most of it, but let it air dry for a day if possible.

An easy modification to help insure that water does not collect at the bottom of the tank is to cut off all but about 3/16" of the pipe on the gas tank side of the fitting. This will ensure that the tank can drain all the way down. Water collecting at the bottom will drain out first and get burned with the fuel, thereby increasing you mileage by 15-30% (just kidding). This, however, my make installing a new filter screen difficult. Some believe that the screen is not needed if you use an in line filter back at the carb line (you SHOULD use one anyway, the earlier VWs did not come with them, VWs filter solution was just the copper screen in the tank). I would use both myself.

I summary, resto your tank by:

The Main Fuel Line

What I refer to as the "main" fuel line is a metal line that runs through the tunnel of the car, from the top of the front bulkhead, to the top of the left frame "horn" down back, next to the tranny.

The Main Fuel Line, Common Problems

This line may rust out in a car that is left sitting, but that is actually pretty rare. It may also get clogged if the tank screen has been absent for years.

If you suspect you line leaking, you may want to do a pressure test. This will require some hoses and fittings, and some ingenuity. It will also require some compressed air. For this you can do several things: 1) Buy a REAL compressor (getting a new power tool out of a car repair should be an underlying goal in your life) 2) Buy one of those cheesy, department store, 12 volt compressors for $19.95. This may be the only use that these things may ever be good for (they take 2.45 days to inflate a tire) as the volume of air you need is tiny, the pressure is what is important 3) Get one of those air tanks for about $10, fill it up at the gas station, bring it home. 4) drive your car the gas station and use the air hose there (it is up to you figure out how to drive to the gas station without the use of you main fuel line).

You need to plug up on end of you fuel line. I do this by pushing a short 1/4" bolt that has a smooth shank under the head (ie. not threaded all the way up, these will not work) all the way into a few inches of new fuel line and placing a hose clamp around it at the end. Then I slip the other end of the hose on to the metal line end and clamp it with another clamp. Now what you need to do is apply compressed air into the other end and 1) listen for leaks along the tunnel sides and/or 2) do a "leakdown" test. This requires you to be able to measure the pressure inside the line after the air source is removed. I would do this by putting a length of fuel line hose on one end with a standard female compressor air line fitting. On the other end, I would install a pressure gauge. I would apply 80-90 psi, then remove the air source (the fitting shuts off when disconnected, holding pressure in). But I have a compressor and whole box of fittings and gauges. You will have to be innovative. Some of those 12 volt compressors have a pressure gauge built in and will hold pressure when you turn them off. You may be able to clamp a valve stem into a fuel line and use that to apply pressure and them remove, like a tire. You could re-measure the pressure with a tire pressure gauge, but remember that the volume of air that is held by the line is very small. The small bit of air that escapes when you push the gauge onto the stem will cause the pressure to go down each time. You can get a compressor air pressure gauge at a good tool supply store for around $10.

You will never be able to listen for air escaping in the line with a 12 volt compressor buzzing away nearby. You need QUIET. Take the plates off the tunnel top under the back seat, at the front of the bulkhead, between the beams and maybe even take the shifter out and listen in there. 80 psi leaking through a pin hole will make a decent sound. You'll feel really good about not having a leak if you are able to measure pressure and can pressurize the line to 80 psi and come back the next day and find it about the same. On the other hand, if you hear hissing in the tunnel, you will be assured that you have a leak and know that you have to replace you line.

These pressure tests may seem extreme, but they are the best way to determine if you have a leak, or feel good that you don't. If 80 psi of air doesn't leak out in a couple minutes, gas at barometric pressure isn't.

The Main Fuel Line, Recommended Restoration

 Basically, you want to insure that the line is not perforated anywhere, and is open front to back. Use the pressure test above to check for leaks.

The best way to clean out you fuel line, especially if the car has been sitting for some time with residual fuel in it, is with a solvent like lacquer thinner or acetone. Acetone is best if you are sure that the stuff will only come in contact with metal. Use a small metal funnel and a piece of fuel line that you will throw away after you are done (acetone will break down certain rubbers; it is not worth the risk to re-use it) and connect them to the line end at the top of the bulkhead in the front. Place a can or some metal container at the end and "flush" the line with a pint or so of solvent. Run it through a half dozen times or so, then flush again with 8 oz of clean solvent. Finish by blowing out the line with compressed air, if it is available. You do not want leftover acetone going through your carb; if you do not have compressed air, flush it last with clean gas.

You also want to pay attention to the openings that the line passes through at the front and back. A quality rubber grommet works well, but in a pinch you can seal it with some silicone rubber. Try to be neat. You want to keep water from entering the tunnel and causing rust.

If you do have a perforated line, you must replace it. The original line is spot welded inside the tunnel in a few places, but not where it exits the tunnel. Totally removing the old line is all but impossible, unless you are cutting open your tunnel (see "Reattaching the clutch cable tube"). In some years of the Beetle, you may be able to cut the tube under the back seat where it enters the frame horn next to the shift coupling by the tranny nose. You can then pull out that rearmost piece. If you are ambitious, you can cut the line at the front via the hole that holds the pedal cluster (take the cluster out). Once you have done this, you can run a new line. Now, I have never done this, I have only heard it described (if somebody has experience ad would like to detail, please e-mail me). Flexible 1/4" ID copper tubing can be used, but you have to get creative about securing it. You only access to the inside of the tunnel is 1) under the back seat next to the shift coupling, 2) under the emergency brake handle (remove handle, very limited access) 3) by removing the shifter, 4) by the removing the pedal cluster and 5) via the access panel at the very front of the tunnel, between the front beams.

As it has been described to me, a straight length of 1/4" ID copper tubing can be slid into the front of the tunnel and fed into the rear frame horn and coaxed out of the hole. Then, if the length is right, you can reach (or hire someone with small arm/hand) into the front tunnel access, bend up the last 4" or so of the tube and feed it up through the hole in the top of the tunnel. A small hand-held tubing bender should be used to prevent kinking of the line. You can secure this new tube to the remaining section of the old one using nylon tie wraps, but only via the access points (if you don't, it may rattle and drive you crazy). Thin fingers and good long set of needlenose pliers are a must. Don't forget some nice new grommets at both ends.

Fuel Lines Down Back

From the main line in back, protruding from the top of the driver's side frame horn in the rear, fuel is carried via rubber fuel line to a short metal section that starts just behind the fan housing. This metal section carries the fuel safely through the rear breast plate and around the fan housing and must not be substituted with rubber or plastic line. This area gets a lot of heat from the exhaust system. From there a short rubber line takes the fuel to the fuel pump. Assessment and restoration of these lines requires only common sense. REPLACE the rubber lines, use new clamps. Flush out the metal section with solvent and check for leaks.

The Fuel Pump

Your fuel pump rests atop the engine block at the rear. It is "run" by a pushrod that goes down into the block and rides up and down on a lobe of the cam. Two types of fuel pumps are common. The original German ones are identified by a cast top which houses the diaphragm. The top is circular and has small bolts around its edge. They are desired because they are rebuildable. At the time of this writing, rebuild kits were still available. The other type of pump is the Brazilian "throw away" type. These are not that bad, I have used some that lasted many years. But the diaphragm is held inside a crimped housing and these pump are not serviceable. I would opt, and pay a little more, for the German one if it is available, but I would take a Brazilian one instead of walking. Most all pumps have arrows on their connection points to indicate input and output.

 The pump mounts on a plastic block that acts as a guide for the pushrod. These pump "pedestals" are known to crack with age from heat and vibration. When they are cracked, they can be a cause of oil leaks in the engine compartment.

 You can test your pump by disconnecting your fuel line at the carburetor and removing your high voltage wire from the center of your distributor and grounding it. Place the end of the fuel line in a can or jar and have someone turn the engine over a few cranks. With every revolution of the engine, you should see a solid pulse of gas come out of the line. [I will reluctantly admit that I have, working alone on my car or on the side of the road, "pointed" my gas line toward the driver's side of the car and sat inside and cranked while looking back to see gas squirting out onto the pavement. I am NOT recommending this]. If you do not have a steady pulse of gas from your pump AND you have already verified that the path from the tank is open and the tank is full (duh!?), your fuel pump is probably bad.

To the Carb

This is easy. Replace your lines and clamps here and ADD A FILTER if one is not there already. Whether you use the screen in the tank or not, you should always use an in line filter between the pump and the carb. These clear plastic filters are readily available at any auto parts store. I used to buy a pocketful at the bug shows for around $1 each. Inspect them every time you set the valves (4-6k mi) and replace them every 10k regardless. These filters have an arrow on them to indicate flow; having air or bubbles in them is normal.

And lastly, there is a known problem with the connection of the line to the carb. Many a VW has burned to a charred shell because of this. The brass fitting to which the fuel line attaches on the carb is just pressed in to the carb body, just above the bowl. Often, this fitting pops off and the pump floods fuel all over the top of the engine block. In the running engine, it is sucked up into the fan and creates ample fumes. The fuel also will drip down over the heads and hot exhaust manifolds and POOF!. Gravity insures a steady flow of fuel to feed the fire once the rubber lines burn through. Pretty scary.

There are some good articles on the 'net about the specific causes, carbs and solutions for this, but I don't have them nearby at this time. The ideal solution is to replace the brass fitting with a threaded one and tap out the carb body (requires the carb be removed and disassembled). Someone was making a retrofit kit for this. Other less sophisticated solutions have been to attach a wire bread tie to the hose clamp and secure the other end to one of the screws on the top of the carb. At the very least be warned. In my next revision of this article, I will have all the details.

Before or After?

I have received numerous e-mails from people saying that the best place for the filter is before the pump, but in the engine compartment. The reasoning is that this is a low pressure line and it is less likely to pop off if poorly clamped. Other's say that after the pump is best as it will catch the debris of a deteriorating pump diaphragm. Still others say use two, one before and one after.

As above, I say put one after the pump, between the pump and the carb. Because 1) I have seen discoloration of well used filters due to pump diaphragm debris 2) 2 filters is overkill and 3) any "reason" born out of negligence (failure to keep your fuel system in top shape) is no reason to do anything. I'm referring to not keeping a filter well clamped in the high pressure side of the pump.

In summary, give your thirty-something year old fuel system some attention before it fails you and requires attention on the side of the road. Don't be cheap, replace ALL rubber lines and clamps and the fuel filter as well. The risk of running a poorly maintained fuel system is far higher than the cost of some new lines and hardware.....

Copyright© 1997; John S. Henry

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