A possibility:
Check FIM`s FAQ, question 8: http://www.fuelinmoto.com.au/

Failing main bearings causing flywheel wobble, does not sound good....

this FIM FAQ / article was one of the first things i read about causes for misfires when I first got my 907 - over two years ago...
Yes, I was quite worried when I read it, too...

the article isn't quite correct - the 907ie sensors are on the crank and the jackshaft (like the later models referred to).

I think the amount of "wobble" on the crank to cause the sensors to bugger up would be very severe bottom end problems - I don't think I have these....yet.

The comment about gear backlash in the jackshaft is a possibility - but I have discounted this - my reasoning is that the motor (crank) is driving the valve gear and that friction in the desmo valve system will keep the gear teeth in contact - maybe the lash would be observed under deceleration...???

I'm not in a hurry to split my cases while the bike is still running OK.
I haven't had a lot of time to do more kms lately but the few rides that I have had since the ciggie butt I don't get the misfire anymore.

a few more hundred kms since the last post...the bike hasn't stuttered again at all...
a lot of this has been freeway cruise where the misfire was previously most noticeable.

my mate suggested I remove the line with the filter to see if the misfire comes back.
I was kinda frightened by that thought...

How about fuel pressure? I just installed a replacement pump which put out a full 3 bar (44 psi) and the bike now runs without any slow speed hesitation whereas before the original pump went south completely, I was having the stumbling. Just a thought. If you remove the tank and place a direct reading pressure gauge on a T after the fuel rail but befor the fuel pressure regulator, thern replace the tank with the gauge and feed line out the left side, you should see the pump build to 40+ psi with just the key on (no start). When the relay times out (4-6 seconds) the pressure will of course drop off as the fuel returns to the tank. If you don't see this pressure, you may have a failing pump. Just a thought...

I did replace the fuel pump early on..
the original had a crack in the outlet in the tank
line pressure was still OK at 3 bar but I didn't want it to fail on me somewhere out in the sticks...

The 907 fuel injection system is a bit of a dinosaur and I expect it was about as refined as they could manage in 1991. It's all the same gear as Ford Cosworths and some other racing cars - so I can't be too critical...
I have some suspicions on various parts of the fuel delivery:
the regulator
pump duration timing
line types
anyway, at this stage my bike is running fine.
the whole hesitation / misfire issue went away when I put the cigarette butt in the line...

Hi all,

I'd like to pose another posibility for our misfire problem;
I've had this problem for a couple of years now and recently I installed the "ciggie-butt tweak". Since then I encountered the misfire once when I rode on the highway.
Then I remembered a problem I had with a previous bike I owned; That bike also had a misfire problem due to a crappy exhaust system. What happened with this bike was that unburned fuel mixture ignited in the exhaust system while air entered the exhaust system at the place where the exhaust pipes were screwed to the cilinder head. When I replaced the exhaust system of that bike, the misfire went away. When I looked inside the old exhaust system of that bike, I saw white markings from the inner-exhaust combustion.
Now back to the 907; When I checked the clamps that mount the exhaust to the heads, each nut was kind of loose. I was able to retorque them; the nuts could be tightened more than half a turn! Since then I havened had any problems (yet....). Even while driving with 22 degrees Celcius....
So I recon the misfiring of our bikes could also be the problem of air leaking inside our exhaust systems.... Maybe someone who is encountering this misfiring problem could double check this by removing his exhaust system and check for white combustion marks inside of the pipes???

Hope this helps you guys solving your misfire problems....
greets,
Sebastiaan

22 degrees celcius??? lol
I live in Queensland Australia - in summer it never gets BELOW 22 degrees for weeks...
we would regularly ride in 40+ degrees.

But Yes, temperature is an issue - it seems to only happen when the engine is hot (80+).

The exhaust sealing was one of the first mechanical things we looked for...
we didn't remove the exhaust but made sure the sealing was good.
the problem is a misfire - not a backfire...
if it was backfiring I'd be inclined to look for imbalance between the intakes (which there was, too...) or exhaust air leaks.

I'm sorry the ciggie butt didn't work for you...
How bad was the misfire before and was there any improvement?
It has to be TIGHT - not to seal it off, just to be very restrictive.

Hi Laddie,

Sorry for the late reply, but I was busy with study and finetuning the bike

But I think my problems are over. In the old situation (without the sig-butt) I had to increase the mixture in low-rev situations by turning the CO-screw kind of rich. Otherwise it was kind of a harsh ride below 3.000 rpm. In the new situation (with the sig-butt mod) I was able to turn the mixture down with 1 turn. It now runs beautifully from 2.000 rpm all the way to redline!
Thanks for your info; another pleased 907-rider here

Greets,
Sebastiaan