Fuel Pump

Fuel Pump

Is this an electrical part or a mechanical part?  You be the judge.  It is on the chassis, so I put it under that category.

The fuel pump assembly (with an integral pressure regulator) resides inside the fuel tank.  If you power the electrical system from a 12-volt battery in place of the capacitor, you can hear the fuel pump run for a second or two prior to a starting attempt.  During this time, the fuel pump draws a current of approximately 1.5 amperes.

With the engine running, K-Scan reports the fuel pump voltage to be almost exactly 15 volts, whereas it may be only about 11 volts when powered via a battery.   This “additional voltage” comes from a separate stator winding (discussed in the Stator section) and a DC-DC boost converter inside the ECU.

I have been told by a reliable source that the pump is a KTM unit and very similar to those used in the EFI Vertigo trials bikes.  The pump itself is marked “Made in China.”

Fuel Pump Operation

There is a fine screen on the suction side of the pump to prevent debris from getting into the pump.

Note the position of the fuel filter.  Fuel flows through it in the direction of the arrow and is constantly circulating through it (not just once through).  That way, the outlet pressure is not affected by dirt in the filter.  I am told that the dirt in the filter is primarily carbon residue from the DC motor's brushes.  

There are two quick-disconnect fittings inside the fuel tank.  A special tool (available at auto parts stores) is required to separate them.  In the photo, an electrical connector is partially obscured from view by the male side of a quick-disconnect fitting.

The pressure regulator is not adjustable. 

Draining the Fuel Tank Completely

I guess I've been lucky with my fuel pumps.  I've never actually had to remove one.  The photos shown here came by way of other OSSA owners.

One owner wrote to me saying, “I’ve had to replace two pumps and it is a nightmare of epic proportions!  Essentially the whole bike must be dismantled except the front wheel!”

When I store an OSSA for the winter I siphon out as much fuel as possible (so I can start with fresh fuel in the spring).  But this still leaves a substantial amount in the tank.

Ideally, there would be no fuel remaining in the tank if you need to remove the pump.  One owner told me he hung the bike upside down to let all the fuel run out of the filler hole.  Another said to siphon out as much as possible and have a large drain pan underneath to catch the remainder when you remove the pump.  I guess you could also run the bike until it stops - assuming that it runs.

I decided to store my 280 for the foreseeable future and figured there had to be a better way to completely drain the tank.  If it was a car, I would pump the tank dry by jumpering the electric fuel pump.  The OSSA is a little harder to jumper than a car, but it's very easy using K-Scan.

Firstly, disconnect the fuel line from the injector.  Install a male/male hose barb and extend the fuel line so it can discharge into a container.  Then use K-Scan's fuel pump test until all the fuel has been pumped out.  Each test cycle runs for ten seconds.  It took ten invocations of the test to fully drain my tank.  I got out over half a liter.  You can hear the fuel pump running while it is pumping.  Once there is no longer fuel in the tank, it's very quiet.

When you want to run the bike again, add fresh fuel and use K-Scan (this time to prime the pump, purge any remaining stale fuel, and get all the air out of the line before reconnecting the hose to the injector).