[Ducati] Help (NDC)

[Stephen Abramson]

It's not for the 900, but I have to ask to pick the collective brain of the
list for help. As an coach for Team ProMotion at Shenandoah/Summit Point
this past Saturday, I left the pit on my '98 Gixxer 600 (extremely
dependable-has never let me down until now..) to lead the Intermediate group
on the first session of the day. Halfway through the first lap, as if you
flipped a switch, the motor began to run as if you shut down a couple of
cylinders. Felt like a cross between en electrical issue and like you had
put the motor on full choke. Applying more throttle resulted in no gain in
speed, just a burbling type of running. Made it back to pit, motor would now
not start at all. Start poking around, the usual suspects given the type of
malady at hand. Pulled the airbox, and found a bunch of fuel sloshing around
in there. Checked electrical connections. (This bike is fuel pump in
tank/carbureted). Normal startup pump process is as follows-flip toggle
switch mounted by tach and hear fuel pump run-runs for approx. 4-5 seconds
and then shuts off, just like the Ducati. I assume this means it has reached
its normal operating pressure, shuts off, and is an on demand pump that goes
on and off while you are riding based on the needs of the float bowls. So
the pump cycles off properly. I pull the hose from the fuel pump, flip the
toggle-fuel pumps out the hose at what appears to be more or less normal
pressure. So the pump works. At this point the bike still won't start. So
I'm thinking maybe a stuck float or something. In any case, I think there is
way too much fuel in there right now for the bike to run, so I disconnect
power to the pump, and start cranking the motor. After many seconds of
cranking, it starts to fire- a little more and more, until the bike actually
starts and runs. Blip throttle a few times, the motor cleans out, and
actually runs cleanly-big blips, nice clean revs. I think, well I don't know
what happened, but it seems to be fixed. (How cruel life can be to tease me
this way). Airbox back on, tank down, seat in place. Try and start
it-nothing. F*ck. Take it all apart again. Pull wire from fuel pump again.
Crank, crank, crank, motor starts slowly, cleans out, revs clean. This time
while it is revving clean, I plug the fuel pump back in, and lo and behold,
after about 2 seconds, the motor loads up again, and basically starts the
bog process and then shuts down. Won't start again. Hmm, let's try that
again. Pull fuel pump wire, crank, crank, starts firing, cleans out, revs
clean. Plug in fuel pump, 2 seconds later it starts to bog and then shuts
down. (Dead battery now....f*uck again..)Get battery charger/jumpstarter.
Try the whole thing one more time, same thing. OK. So there are these two
little black mystery modules located behind the carbs under the tank. Each
one has two wires going to them. One of them has a hose that comes out of it
and splits to two of the carbs as well as a hose that goes to the airbox.
The other has the same stuff, one hose that comes out of it, splits, and
goes to the other two carbs as well as a hose that goes to the airbox. So
I'm thinking that these mystery modules are pressure regulating devices to
somehow control the pressure or amount of fuel to the float bowls. If one of
them has failed, maybe there is an over-pressurization to two of the carbs,
creating a super rich situation, which goes along with the symptoms the
motor exhibited as it started to bog and shut down. When we disconnect the
fuel pump, it allows only the fuel that is sitting static in the bowl to be
delivered to the carbs, and as soon as you introduce fuel via the pump, we
have an instant over-rich situation. I think this electrically based fuel
delivery problem could be the case based on how quickly the problem came
on-it was instantaneous, as if a physical component failed, as opposed to a
quick onset problem that was purely fuel based. I suppose there could simply
be a stuck needle, but I'm leaning toward  the mystery module. I flogged the
bike for two days at Calabogie two weeks ago, riding one, sometimes two
classes as a coach, and battling on my own within the expert class while not
coaching. Bike was put away and not touched since that time. Gentlemen of
the jury, have you reached a verdict? Thanks for your consideration.

 

Steve