Yager fuel pump

[CROSSBOLT]

Does anyone have any idea why the Yager fuel pump has a vacuum line to it?

Karl

[marty]

Vacuum operated fuel pump maybe (common in karting)

Are you sure its just not a vacuum operated petcock?

[CROSSBOLT]

Thanks for calling back, Marty. It is confirmed as an electric fuel pump for the Yager's EFI system and I can see wires running to it separate from fuel gage which is also electric. Fuel petcock or shut-off? Maybe, but I do not know.

Karl

[gregspeople250]

Vacuum operated automatic fuel on/off.  Many scoots have them; maybe most.

[CROSSBOLT]

That would make good sense, Greg. All the bikes with gravity fuel feed have vacuum operated fuel taps. This fuel injected model has the tank below the foot board and needs a healthy pump for the FI. The computer runs the pump for a few seconds before engine start without vacuum because I can hear the pump shut off when it is real quiet. Once the engine starts there will be some vacuum to keep the pump running. Thanks!

Karl

[MotoRandy123]

Actually the fuel pressure regulator is built into the mount for the fuel pump in the tank,
the vacuum hose modulates the pressure mainly to lower it at idle. My BMW K75 has a
similar setup. On the BMW you can disconnect it with virtually no difference. I think it
saves gas as less presure = less fuel used at idle.

[CROSSBOLT]

I think you are on to something, Randy. I closely examined the service manual pictures and text and it indicates "regulator" at top center of fuel pump exterior. Your experience with the BMW system may be the clue. Will advise.

Karl

[CROSSBOLT]

Disconnected the vacuum line to the fuel pump and plugged both the vacuum source and the hose to the pump assy. Test ride and idle seemed to be unaffected. Will advise after a few more hundred miles.

Karl

[CROSSBOLT]

The final analysis on this is the Yager used more fuel with the vacuum hose disconnected since the fuel pressure was not reduced at low engine speeds (higher vacuum). I hooked it back up just before I traded it. All this was because the bike developed an intermittent habit of hesitating or fading in power at either acceleration or steady throttle. I suspect it was a "fuzzy" throttle position sensor.

Karl

[MotoRandy123]

The pressure regulator could have had something to do with that. You'd need the fancy factory computer
to do further tests to be sure. I guess it's the next guys problem now! I should have held out for a bigger
bike I think. Those 300i's look nice!

[CROSSBOLT]

Ride real nice, too! Hey! She MADE me do it!