Hi all I am looking for some pointers/inspiration/help in solving a running issue on my 1992 900 Supersport. Long story short - I bought the bike as a pile of bits in 2017, rebuilt it and had it back on the road in 2018 (there's a story about it somewhere on here...). Since then it has run well, doing around 6,000 miles and five trackdays (Cadwell x 3, Donington (eek) x 1 and Oulton x 1 - all with Classic Bike Trackdays and all tremendous fun). I have had the bike out on the road a few times already this year from March onwards with no issues. I have a trackday coming up next weekend at Cadwell. I have just been away for a couple of weeks in Spain on my Multistrada, so began the prep for Cadwell a few weeks back. I checked the bike over: belt tension, bearings, fasteners, brakes and so on - all good so then I went to run it up the road to check it was running OK. All was not well however, with it being very hard to start, popping and backfiring all over the place, and when I went to ride it - thinking an Italian tune-up" might help - it was dreadful. Starting with electrics, I followed the diagnosis in the Haynes manual. The spark plugs looked OK and were sparking, but the spark looked pale and yellowish, rather than the fat blue expected. I checked the resistances on the pickups, both OK (97.5 and 99.3 ohms). Primary coils were good at 3.8/3.0 ohms and secondary coils also OK at 11.8 and 11.76 ohms. All good. I also inspected the wiring and the wiring for the pick up coils to the ignition does look a bit ropey - all the kit is original, and the primary pick up wiring is that cloth-bound stuff and the outer sheeting does look quite frayed and worn, though there is no obvious sign of breakage on the inner insulation/wiring, and presumably if there was, this would have been picked up by the resistance test anyway. Having, I would have thought eliminated most of the things electrical things required to make the bike run (but noting the yellowy spark), I figured this could be a fuel issue. The carbs were cleaned by the previous owner (a friend) prior to my ownership and the bike ran pretty well once back together, save for a slightly low tickover which I never quite managed to resolve. Nonetheless, having run for 7 or so years, I figured it could be time for a carb clean. I had them out and took them to a guy who does such things who stripped and cleaned them in his ultransonic bath (confirming that they were quite cruddy inside, butt otherwise serviceable) and put them back togetherwith new O-rings and so on. By coincidence, I had managed to pick up a pair of California Cycleworks coils on a FB Group, so figured it could not do any harm to fit these while the carbs were away. Weirdly these are configured differently to the OEM coils, with the primary connections on the top and the HT lead at the bottom. I figured out a way of fitting them, but noted that the HT wiring length is not very generous, and, furthermore, the length of the coil required the HT lead to make quite a sharp turn against the battery tray, which could put it under stress. Once I had the carbs back on the bike (after 4 hours of muck, sweat and tears), I fired it up - to be fair it started instantly and while not ticking over that well, figured i would set the tickover when warm. Anyway, a quick run up and down the road confirmed it still was not well, with an obvious misfire which I judged to be on the horizontal cylinder, based on exhaust header temps. At that point I had to draw a line under it due to the bike trip, but, having got back yesterday (wonderful thanks - the Picos is a must if you haven't been) I am on a mission to get it running right before Cadwell next Saturday. It still isn't running well. I have rechecked all the resistances again - the only change is that the pick up resistances have increased to 109.9/111.6 which is above spec - possibly because I checked them after it had run so they were warm? Not sure if this is a thing or not, but will recheck again later. To eliminate a few other variables I have: Swapped the CA Cycleworks coils back to the OEM coils - no change. Fitted a new plug to the horizontal cylinder - no change. Swapped the horizontal and vertical CDI units over in case one of them is faulty - no change. Re-examined the pick up wiring - still no obvious signs of breakage. When running, the horizontal cylinder seems to be part-firing - coming in and out as you can feel the bike surge. And also the header is hot, but not as hot as the vertical, so there must be some combustion going on, just not consistently. It is turning into one of those horrible intermittent problems which are a nightmare to diagnose. Wondering if anyone has any thought, tips or similar experiences successfully resolved that they might wish to share, before I put a match to it? If I can't fix it in the time then all is not lost for Cadwell as I have the offer of a mate's ST2 to borrow and thrash round, but I'd like to get the old girl there if I can... All help gratefully received, as always. Cheers James
Hi James, Tis annoying when this sort of thing happens for no apparent reason. Assuming you have put fresh plugs in the bike, i had a similar issue at one stage and fresh plugs cured it!!
Also plugs from a reputable supplier, I understand there are a lot of bogus NGK plugs out there, and know someone who had problems with a new Bosch plug (misfire, cleared by putting the old plugs back in). Best case with bogus plugs is a misfire I guess, worst case is wrong plug temp or the electrode being released and falling into the barrel. What a world we live in today……
A couple of checks to do if you haven’t already done. Do a compression test. Also put a strobe light on each cylinder, not so much to check the timing but to check for continuous spark, it’s also a great way to check the igniter boxes are advancing correctly. A couple of ideas
I had issues with the Darmah being hard to start and feeling a little low on vigour and it turned out to be the main (live) feed to the ignition switch. So perhaps check all such connections on the live feed path along with all earth(s) - especially from the battery to the frame.
i'm not sure if you've mentioned these in your lengthy reply, but if you feel that you have thoroughly ruled everything out, and also that the fault is intermittent and appears to run okay at times, then it could be Your flywheel ignition timing trigger failing and/or the wiring to same shorting out or being intermittent. A symptom you describe that helps, is that you say it's on one cylinder only?
.. it's nice when the above fail completely, as relatively easy to find, but often they soldier on, working intermittently, typically could be okay cold and then start to play up when engine is hot. if you want to go totally anorak, you could measure each of the above's electrical Values In situ, but it's not a very reliable test due to notes above.
Thanks guys. Things escalated to the point where it would not start at all (from starting but running rough on the Horizontal cylinder. After a prolonged bout of cranking it coughed then produced a backfire like a pistol shot which left me temporarily deaf in one ear and produced a plume of black smoke from the RH exhaust, which made me think that Ducati had just elected a new pope... At this point I decided to try new plugs and, bingo - it started up first time which makes me think this is where I should have started. That said, though it runs it is still rough on the horizontal cylinder and therefore not fit for Cadwell tomorrow (I'll be borrowing a mate's Gen 1 Multistrada instead). I need to have another round of diagnostics next time I have time to get back to it, but I will check the carb balance (the guy who rebuilt them said he had balanced them on the bench but always worth a check) and thank you Chris - ignition pickups are on the list of things to check - currently the resistances are fine, but it could be a sign of failing if they are intermittent. We'll get there...! Many thanks all James
