I have a 907IE with FIM chip and Two Brothers exhaust that developed a skip from 3K on when warmed up and above 75 degrees F. The bike would accelerate, but not cruise without skipping and mis-firing. I found that the wire leading to the coolant temp sensor was missing some insulation last year and so the problem went away when I repaired it. The intermittent returned again this spring! Following the Laddie "ciggie butt" remedy, I drilled out a .187" lead pellet to .060" and put that in the Pressure sensor line to dampen the pulses in the air box. When that didn't work, I went to .040" restriction. Finally I reseated the connector to the Coolant temp sensor and the bike runs great again! I left the restrictor in the pressure sensor line because I think Laddie's fix can do no harm even if the intermittent is something else. The lead pellet is easy to drill and slides nicely into the line if you want a non-smoking bike

The 0.040 (1.0 mm dia) restriction is too big - still allowing too much air transfer. The air port on the sensor [that the vacuum line plugs on to] is only about 1.0mm diameter so the restriction needs to be (much) less than this.
You need some pressure transfer but not much at all. The filter is just to damp any pulses.
We watched the thing on an oscilloscope before the ciggie butt; the sensor was all over the place. We even rigged up a 5 volt battery power supply to smooth out any power influences. Unfrtunately I can't tell you what happened to the signal after the butt; we didn't test it afterwards.

Before, I could not hold a steady throttle between 3000 and 4000 RPM; it dived up or down thru this rev range - no matter how hard I tried. On the road (in gear) of course you have flywheel effect of the drive train so you can hold a cruise speed but the misfire is apparent. The sensitivity went with the ciggie butt.

It may be caused by an intermittant (heat related) or partial backfire thru the intake? I dunno; whatever it is the ciggie butt damps the pulse and (for me) stops the misfire.

the ciggie butt needs to be jammed "tight"...so you need to really force any air (pressure) transfer.
sorry there's not more science to the description...yet.
I expect a sintered filter or line type fuel filter will be a reliable non-smoking device; finding the right one with the right restriction might be a chore.

I have a spare sensor; I'll try to play with it (and appropriate restrictions).
It really needs to be done with an oscilloscope on a running bike, one day...maybe on a dyno. It would be interesting to observe any changes to acceleration curves...[although i don't know if anyone is still interested in getting peak performance out of these dinosaurs...]

I know exactly what the misfire is like and can sympathize with you...and even I don't believe that this "trick" works...but I've clocked up a few thousand kms since. I couldn't enjoy riding the bike before this.

gimme some feed back please; quite a few guys have told me it works for them or at least improved the problem.

For Sale;
Tune Up Kit For Paso:Four old ciggie butts
One box of matches (in case tune up not going so well)

Morning Laddie! ............................Marty

hiya Marty...
maybe soon 907s will be sold as "filters" and "regulars"...

I have a lazy $50 says if Shelboss fits the butt correctly his problems will be filtered away...

hope things are nice 'n brisk in the Apple Isle;

cheers mateeee...

Hi Laddie, I did some testing of restriction in the line with a vacuum gauge. The 040" restrictor bleeds down from 20 HG to zero in 2 seconds. The cigarette filter in the line takes about 15 seconds, big difference! My skip came back, so I installed this in the line and went for a ride. It is not working for the problem I am having. Mine seems to act up most on deceleration, like the engine is cutting out and in again. I still suspect it is the coolant temp sensor. I may try a fixed resistor next. Sure wish I plug in and watch the ECU while it is happening! Anyone out there made a diagnostic tester for the 907?

hmm - 15 seconds for 20mm HG pressure change is maybe toooo tight, but shouldn't interfere with deceleration...I would expect a vacuum lag [back to shut throttles] to make the ECU deliver more fuel than less until the sensor pressure came back to air box pressure.

I suggest for the process of elimination you only change one component at a time.
can I recommend to pull off the restricted line [and refit an unrestricted tube] until you're satisfied the WTS is eliminated.

the WTS can be replaced with a fixed resistor as a temporary measure. I would choose something around same resistance to 80 deg. [Watch your temp gauge].
Marelli have the heat / resistance chart for the sensor on their site.
or
You can just pull the wire from the sensor - the ECU has a limp home mode that will select a suitable fixed number for resistance for the map.

You can test the sensor with a multimeter through the heat range in a pot of heating water; I replaced a bad one that dropped out at about 90 deg but it didn't make any difference to my problem...go figure!!!
It would be possible to rig up a multimeter to the WTS and watch for dead spots.
It could be done "on road" but suggest you get a reliable pillion to watch the meter on some straight highway. Suggest you connect to the ECU so you are also checking the wiring (which you indicated was suspect).

Shellboss, this is probably in the sucking eggs category but how is the condition of your battery? I had a similar "missing on deceleration" issue that I think was related to low system voltage (compounded by voltage drop in crappy wiring). It was most evident below 3-3500 rpm as that is about where the output of the alternator drops away. It went away with a happy battery and cleaned up wiring. Of course now I'm getting the stumbles at cruise and will be doing the Camel mod shortly to see if it goes away.

Cheers
Andrew

I just put a new battery in this year, all connections and grounds are good, at least the ones I can see. I may reseat the ECU connector just to see if any difference. I pulled the WTS connector and the only difference was the bike not revving up with the fast idle lever. Time to make the ECU tester!

Greetings. I am new to the list but have lurked off and on for a year or so.
I have a 1992 with about 13,000 miles. It was set up by Bruce Meyers of BCM Ducati in New Hampshire (a noted duke race engine builder) a couple of years ago with what I thought was V2 chip. It has a K&N, opened air box and aftermarket slipons. It runs very strong and is delightful until the fuel level gets to about 1/2 tank and it is warm. It then develops a misfire at about 3000 rpm similar I believe to what Laddie and others have described. Two things cure the problem. One is twisting the throttle and feeding more fuel. This has obvious drawbacks since auto bumpers become problematic as do our posted speed limits. The other thing which seems to cure the problem is to topoff the fuel. This makes me think there might be a leak in a fuel line in the tank which sucks air when the level gets to the leak. Anyone have a similar experience? Are there rubber fuel lines in the tank? Should I do this in addition to the cig filter fix?
Thanks.

I would think that air in the fuel system would lead to rough running throughout the rev range and at any throttle position...but maybe

Rich,
it's unlikely to be a leak in the fuel line drawing in air.
the fuel pump pressurizes the fuel line to 3 bar (about 50 PSI) so not much air will get "in"...unless it is drawn directly into the pump intake.
The retun line to the tank has a "de-gassator" in the tank - which is supposed to de-gass any returned fuel.

for a while I was convinced it was air or gas bubbles in the fuel, too...but the misfire seems to disappear at various conditions:
1) at idle
2) over 5,000 RPM (maybe flywheel effect?)
3) accelerating makes the misfire disappear
all of the above should discount the air leak theory.
If there was air causing the misfire it would also be present under these conditions too.

I'd be interested if you would try the ciggie butt and see if it works for you.
depends on how modified the air box is...

If I was you I'd be taking the bike back to Bruce Meyers and asking him what the problem is...

Okay Laddie, I finally nailed down what my problem was, the TPS was set to 40 mV with the butterflies closed all the way and the spec is 150 mV. My warm weather problem was unchanged by the ciggie-butt mod, and got worse when I put a new air temp sensor in that was closer to spec. The only thing I can figure is someone compensated for the bad temp sensor with the TPS setting. Anyway, it runs great even down at 3K rpm! The procedure for tuning the fuel injection is on FIM's web site and is very straight forward, just need a multimeter and a mercury balance gauge.

It doesnt need to be mercury gauge. In markets there are plenty of otherkind meters also for that balancing job...

ahh, the good ol' TPS...amazing what effect it can have...

at 40mV you were telling the ECU you had twisted-shut and torn the throttle off the handlebars...lol...my guess is there was NO fuel getting thru; any wonder the engine was cutting out.

vacuum balance is important; if you check the balance have a look at idle and (say) 4,000 RPM.
the throttle bodies can be very close at idle [with the air bleeds shut] but way out at 4,000 RPM
I found it best to balance to within 10% on the butterflys and THEN try to get the balance right at idle with the air screws.

most of the stuff I have read about vacuum balancing only tells you how to set it at idle...

as our learned collegue Finnpaso suggests - you don't need mercury guages but you must get something that is DAMPED (or suited to twin cylinder balancing) - otherwise the intake pulse makes it difficult to read...and you'll never guess what you can damp the pulse with...

standard vaccy guages aren't damped - so you can diagnose other engine faults on multi-cylinder vehicles.

hope it all comes together for you.

I have a friend that made a balance tube using clear tubing and two stroke oil in a loop. I tryed this without the restrictors, what a mess! Yes FIM's instructions set the TPS first, the mid-to high end sync second, and the air bleeds for idle last. The balance at mid to high end crosses over at about 4500 rpm. I wonder if the newer FIM chip does a better job at keeping it constant throughout the rpm range?