851 rev problem

[B.Rock]

Just for fun, open the cap and turn the key on, see if there's fuel flying around inside the tank when the pump's running.

Brad may have been serious for all I know....

Sure, good call.
Also it seems to be rev related and not load - I'd expect a fuel system problem like that to be load related?

[brad black]

i was serious.

[ducpainter]

i was serious.

seriously?

[brad black]

on at least 2 851 that i've seen with a complete shut down symptom the cause has been a voltage spike apparantly caused by the regulator.  altho these, like all over vibration issues i've seen with 4v bikes, happen at 7,500 rpm.  loose engine mounts may bring it lower, as i guess could cracks in the cases between the mains and timing shaft, but that's an extreme issue.

they shut down, the ecu turns itself off to protect itself from the spike, then turns itself back on, gets its shit together and starts doing its thing again.  and because the revs have dropped due to no power it'll come back, hard if the throttle is still open.  probably shuts down for a second or two, feels like an eternity.  then it'll charge back to 7,500 and shut down again.

originally the regs were mounted with well nuts holding them to the frame.  there was a service bulletin saying to solid mount them (reg earth wire issue maybe?  i forget) and on a very small number of bikes this miss would suddenly appear at some time (long time) in the future.

so you'd replace the nuts and washer with well nuts again.

dunno if it's your problem.  personally i'd certainly check it, but that's up to you.

[B.Rock]

Thanks, I appreciate that. This isn't that long, it's about 1/4 sec, only enough time for the revs to drop about 500-1000 rpms before it picks back up. Since I'll be home during the daytime I'll pull a couple other things apart, clean, and reassemble to try today.
Does anyone have any idea what the diagnostic tool is they refer to in the manual that reads the flashes? It doesn't look like the Mathesis. That's just a curiosity thing.

[jerryz]

could be fuel stravation caused by old fuel filter it happens often on Ducatis with EFI

[B.Rock]

I tried bypassing the filter, no change.

[greenmonster]

Thanks a lot (again), Brad!   

Your tip cured a 916 SPS which cuttted hard at 3000 RPM.

[B.Rock]

So after I punted and took it in for service anyhow and had them give it a look, I've got it back.
The verdict: who knows, sort of. It went away after they did valves and belts and some other nonsense, which included replacing a wire that was in poor shape coming off the stator, which was all corroded and cracked. Since it wasn't intermittent before and has now disappeared entirely, I think it's quite likely it was related to a voltage drop due to that wire. At least, for lack of anything else relevant being done.

[B.Rock]

So after I punted and took it in for service anyhow and had them give it a look, I've got it back.
The verdict: who knows, sort of. It went away after they did valves and belts and some other nonsense, which included replacing a wire that was in poor shape coming off the stator, which was all corroded and cracked. Since it wasn't intermittent before and has now disappeared entirely, I think it's quite likely it was related to a voltage drop due to that wire. At least, for lack of anything else relevant being done.

It came back and left me stranded. Fuel pump totally failed.