851 rev problem

[B.Rock]

So, my 1990 851 has an issue where it will start and idle fine, but when it revs to 5500-6000 or so it will sort of bounce back and never get above it, like it momentarily cuts out. If you keep the throttle open it will bounce between 5-6k rev up, cut off, rev up, cut off, repeat ad nauseum. It's a pretty hard cut off. I've replaced the wiring to the pump and tried it bypassing the fuel filter so I'm pretty certain it's not that. It does it in gear, neutral, uphill, downhill, etc.
It's like it's trying to change something - ignition, fuel, ? - to another rate for higher revolutions or load and can't do it.
My basic mechanical skillz are okay but electrical diagnosis is voodoo. I can connect a voltmeter and read stuff but once it gets into things with acronyms I'm a little lost.
For those not familiar, the 851 is 4v, fuel injected.
Any ideas? Thanks!

[greenmonster]

The very best place to ask is here:
http://www.ducati851and888.com/index.php

Tremendous amount of knowledge there!

[Raux]

any recent service or work done?

[B.Rock]

any recent service or work done?

No. Well, the last work I had done was to the fuel level sending unit at Desmotosport, and that part failed again, so I replaced it. I had thought the rev thing might be an issue with the sending unit - like starting to go before it crapped out entirely - but no joy.
It needs to go in for valve service, and if I can't figure this out I'll limp it in and pay someone to do it, but it's pissed me off some and I want to conquer it. Particularly because I let it sit some so I could do it.
I forgot to mention, I have the service manual so tracing stuff is not too much trouble, but as far as why to check any particular thing it's pretty worthless.

[Raux]

sounds like fueling issues

not enough fuel at higher revs?

[B.Rock]

That was my original thought too. Or my original hope. So that's why I started there. I suppose it could be in the injectors but it's such a hard cut-off... Fuel pump draws power from the relay and the coil, and I know the relay's powering it. My thought was if the coil-pump connection was kaput then it was more just starve itself and not rev well at all, but it does - until that hard cut. Also, it will backfire sometimes after that cut which leads me to believe - hopefully correctly - that it's getting enough fuel but spark is being cut. 

[Raux]

well hopefully one of the smart guys will chime in here shortly

[greenmonster]

Brad will come f sure....

[B.Rock]

Right on. The more and smarter the merrier!
Tonight I'll pull the TPS connector and give that a cleaning, I suppose.

[ducpainter]

It sounds like an ecu issue to me.

[brad black]

if the voltage regulator is solid mounted, rubber mount it.

if it's rubber mounted, solid mount it.

[B.Rock]

OK. Why?
I checked the phase sensor and crank position and both were clean, no debris. I didn't get voltages since it was midnight and people frown on running the bike then. Not me, other people.

[Speeddog]

My bet is on a perforated fuel line inside the tank.

if the voltage regulator is solid mounted, rubber mount it.
if it's rubber mounted, solid mount it.

I think that's a translation for "Not sure mate, but something's rooted."

[B.Rock]

My bet is on a perforated fuel line inside the tank.

Just had all the lines out and they looked good.

I think that's a translation for "Not sure mate, but something's rooted."

[Speeddog]

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....