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Fuel Pump


Bob Peloquin's Overview and Repair

The fuel pump is a simple diaphram pump. There is a set of contacts which close when the spring pushes the diaphram to the end of it's travel, and a solenoid coil to pull the diaphram/plunger to the other end of its travel against the spring.

The contacts are under the top cover which is held with one screw. One wire goes into the cover, the other wire is connected to the frame of the pump. For the non electrically literate, the wire connected to the pump frame is the ground side of the pump.

The contacts can be cleaned with WD-40 and a piece of cardboard, this will remove most stuff on them. The upper contact rests against a rubber bump stop, don't bother cleaning the top side of this contact. Don't lose the bump stop, otherwise the pump won't work.

After you use solvent to clean the contacts, look carefully for burn or irregular pit marks. If there is noticeable irregular roughness to the contacts, you can smooth them out with a very fine file. The file on a pair of nail clippers will work in a pinch. Go easy, you are just trying to smooth out the rough spots, so don't try to file down Mount Everest. If you don't remove enough, you can try again, but you can't put ANY of it back.

After cleaning and/or filing the contacts flush them off with some solvent, NOT WD40 or anything with oil in it. You can use lighter fluid or even some gas. Leaving oil on the contacts will cause you no end of grief down the road. The oil will burn and coat the contacts with an insulating layer - not what you want here.There are 6 screws holding the valve body in place. Inside there are two check valves that may have fuel tank crap stuck in them.

When you remove the valve body, note where the fuel line fittings line up, as if you reassemble it incorrectly you won't be able to install it back on the bike. A scribe mark helps you to remember the correct position.

You can flush out the valve body with a hexane based or a rubber safe brake cleaner. Check for crap stuck in the check valves. If there is anything lodged in either valve you will not get any fuel to the carbs, and the pump will just move fuel back and forth in the fuel lines. see Footnote 1.

Check the diaphragm for cracks or tears, if there are any, you will need a new pump. Pressing in on the diaphragm should open the contacts and there should be a some resistance as you push against the spring. The diaphragm should pop back when you release pressure on it, and the contacts should close.

If you have a dvm (digital volt meter), check the resistance of the contacts, the meter should read 0.1 ohms or less. Check for continuity of the coil. Clean and tighten the terminal that is screwed to the pump frame.

Now you have it all nice and clean, reassemble the valve body and evenly tighten the screw in three steps so you don't distort the gaskets. Don't overdo it, you are not tightening 1" bolts. You did add a scribe mark so you could assemble it the right way didn't you?

When looked after properly, and not stored for years in a hostile environment, these pumps can almost last forever. The one in my V45 has 120k miles on it and still works fine.

Footnotes: 1. If you jumper the cutout relay connector as per the flow test and your pump runs continuously with fuel in the tank and everything else installed, there is likely some junk holding one of the check valves open. Time to replace the fuel filter and flush the lines clean before you reinstall the pump.