Skip Faulkner's Fuel Tank Mod

This is the text of Skip Faulkner's fuel tank mod, supplied by Kurt Simpson. In short, it is a procedure that will make your "main" fuel supply consist of the main body of the tank and the fuel in the right "lobe," and the "reserve" supply consist of the fuel in the left "lobe." This was originally posted to the DSN_KLR650 mailing list; I'm not sure if it was published in DSN. Since the original writing, some errors and suggestions have come to light, and I have included them in the body of and after the end of the text. If you have more information, please contact me.

-Chris Krok

Parts list:

Ive been trying to finish this post for the last four nights, but every time I start it, I get called out. Weve been having a lot of fires around here till the last day or so (got a little rain) and my place does the maintenance for the state fire aircraft. Im finishing this tonight, so you might as well climb up on the fence and sit a spell. Last week we had a thread going on the unusable fuel on the right side of the KLRs tank. The general plan was to install another petcock or fitting on the right and run a hose from it. Many were worried about welding on their tank or using an adhesive for the fitting.

I got to thinking of another possible solution and experimented around with it several nights ago while waiting for the choppers to come in. Ive been using it for several days now and it seems to work very well. First Im going to give a description of the petcock system (from here on referred to as the fuel valve) for those unfamiliar with it. I apologize to those already familiar with it, but I learned a little myself.

If you look at the valve from the left of the bike (how else) you will see two hoses. The larger of the two coming down from the valve is the main supply line and the smaller hose coming out horizontally from the valve is a vacuum line that operates a springed diaphragm valve on the back of the fuel valve. This smaller line is routed to a position downstream of the carb throttle. There have been some Listers who have removed this vacuum line while removing emission controls to find out that the engine wouldnt run. The purpose of this diaphragm valve is so fuel cannot pass through the valve without the engine running. Because of this, I use the following method to drain fuel from the tank.

To drain fuel from the tank (which you must do to do this mod), you first remove the supply line (larger line) and attach a inch ID line to the nipple on the valve and run the other end into a container. Then remove the smaller line and attach a 3/16 inch ID line to the horizontal nipple. Suck on the smaller line and while holding the pressure, clamp the line with a pair of hemostats or any suitable clamp that will squeeze the line tight. At this point, fuel should start to drain out of the larger line. If not, you may have to suck on it to get it started. To stop the flow, simply release the clamp.

To completely drain the left side of the tank, make sure the valve is in the reserve position. There are two bolts with Phillips indentions to be removed to drop the valve. Once released, drop the valve gently so as not to damage the screen inlets. Before this valve is removed I recommend getting a new o-ring from Fred or your dealer in case you damage the stock one. Once the valve is dropped, you will see a 5 standpipe with an inlet screen on top. This is the source for the main position. To the right of it is a flush hole with an inlet screen: this is the reserve source. If you take a flashlight and look down and to the left in the tank, you will see all of this.

After much trial and error, my best result was to cut 2 off the top of the 5 standpipe (remove the inlet screen first and after the cut, debur inside and outside the cut) and put a slight bend in this pipe to lower the height of the point where I will attach a length of polyvinyl fuel line (clear). I then twisted the standpipe to the right a little so as to force my hose that Ill be attaching, a little toward the rear of the tank. You may want to try this without cutting the standpipe first. I wasnt worried about the standpipe as it is easily replaced (it is just a pressure-fit).

At this point, I got a 2 length of the fuel line and and fed it up into the tank through the valve opening. I used a parts grabber (those 2 long coilsprings with a syringe type handle at one end and when squeezed, four little spring claws come out the bottom) that can be bought at most parts stores (theyre used for picking up dropped screws and such in hard to get to places) for about $3. I used the grabber to pull the end of the fuel line up through the filler opening of the tank. I then attached a fuel inlet strainer (in tank type) that I had gotten from a cycle shop. Its the kind used in some auto tanks and in some ATV and riding lawnmower fuel tanks. Mine is about 1.5 long, barrel shaped screen with a nipple for fuel line at one end and a bronze spring coiled around it for protection.

After attaching, I placed that end of the fuel line back in the tank and with a flashlight in one hand and the other end of the hose sticking out of the valve opening below the tank ( holding this end with the other hand), I pushed and turned and and pulled and whatever was necessary to get the fuel inlet end of the line in the same position on the right side as the fuel valve on the left. You want the line to curve toward the back of the tank and then come forward . This is also the reason I twisted the bent standpipe to the rear a little, it helps keep the line in a bind.

The rear of the tank has a lower rise in it and also, this curve helps to keep the line in place. I then pushed in a few more inches, careful not to disturb the inlet position and pinched the line where it met the bottom of the tank. I then pulled some line out, keeping my pinched finger in place and cut the line 1 above my pinch. Then I placed a thin film of Dow 4 (you can safely use petroleum jelly ) on the stand pipe tube so the hose would slide on easier, and slid the hose on the pipe to within of the base. Then push the valve back up into position (its a tight fit,but it will go in) while watching through the filler opening. You may have to pull the valve back down and twist the line a few times to get the fuel inlet end of the line in the position you want it in. When I bought my line it had a curl to it. This works in your favor in curving the line toward the back of the tank, but it also prevents the inlet end from completely dropping against the outer wall of the tank, unless your line is more flexible than mine. With time, the line will relax and drop lower. In three days, mine is almost there now.

The above was the end result of a couple of days of trial and error, but it is working well. How this works is like this: This is not a true gravity fed system. The carb on the KLRs has a low pressure pump on the left side. Once I realized this, I figured between the light pump suction and a siphoning action of the fuel coming up from the right side and down again, this might work. [Skip later realized that this was not a fuel pump like some other Keihin carbs have, but the coasting enricher system. The KLR fuel system is gravity feed only. -CK]

I drained the tank via the reserve position before I started all of this.I did this with the bike propped up in the upright riding position. This left only the unusable fuel on the right side. I then siphoned this out into a calibrated measuring container to see how much fuel is actually over there. I measured out 42 ounces the first time. I filled the tank and did it again and came out with 47.5 ounces. I was low on fuel the first time and have since found out that when the fuel is low enough to have the two halves separate, through bumps and lean angles, the fuel will sometime flow over to the other side. Since I started with a full tank on the second measurement, it is the most accurate as to how much the right side can hold. The test results are as follows; I have in the past three days, drained the left side of the tank completely, before going home. While carrying a gallon of fuel on the rack, I have driven till I have run out of fuel. The mileage the first time was 18.5 miles, second was 23.3, the third was 19.9 miles. This was about 2 miles of town (with stoplights) and the rest was highway at 65 to 70 mph indicated.

I was suspecting that when I was bone dry and then filled up, there might not be enough suction from the light pump to start the fuel flowing from the right side, but is has every time. Today I was doing some extreme weaving at low speeds to see if the fuel would cross over and sure enough, at about mile 8 it started to surge and sputter and I switched to the reserve (which is now the left side) and there was fuel there, when I had started, the left was empty.

Once I had decided exactly how I was going to do this, with the parts in hand it took about 1.5 hours. Most of that was just making sure I had the line positioned in the tank where I wanted it and also deciding on the length of fuel line, that part is sort of trial and error. Was it worth it? To me it is. I now have about another 20 miles of range and I know Ill need it somewhere down the line. For those of you rejetting your bikes, you wouldnt have any range loss. The other thing is, this is completely reversible and better than welding on my tank. The addition of another valve on the right side would give you maybe another couple of miles over this method because it would completely drain the right side. For the sake of 2 or 3 more miles Im not going to start drilling holes in my tank. Im sorry for the length of this post. Its late and Im tired and if I had waited till later this morning (its now 1am) I probably could have explained it better and not so wordy.

-Skip (who is gassed out and going to bed)


Harry Thames uses a small horseshoe magnet to hold the end of the fuel line in place; else it might have to be repositioned if the bike is layed down on its left side.

Skip did check with the NTSB, and this procedure does not violate any safety rules, since it doesn't modify the fuel tank. (In fact, you can modify the fuel tank as long as you don't pressurize it.)

The Squasher suggested 1/4" ID silicone fuel line that is available at hobby shops, and may be more fuel resistant than polyvinyl. However, it must have the same OD as the 1/4" ID polyvinyl fuel line, as the OD determines how snug the fit is inside the petcock tube.

There were a few reports of people having fuel starvation problems after doing this mod, but I haven't seen further confirmation. It is possible that something else was disturbed when they did the mod, or they had air in the line or an undersized strainer.