1992 SS900 Carb issues - looking for advice please. Bought my 'new' bike a few weeks ago now and was very pleased!! Has 28k on the clock and had a full desmo service and also the carbs cleaned out and new seals (not done anything with the jets etc) which I thought would provide a great baseline to work from as it wasn't running so well, but being stood still for a few years would explain that. Issue is that between 2.5k and 3.5k the bike coughs and farts and back fires then as you get towards 4k it takes off like a train...problem is all of this coughing makes it really difficult (choppy) to ride at 30 or 40 mph and is causing it to run rich and the plugs are getting dirty, to the extent I can't start the bike when next want to use....new set of plugs and its away almost immediately. Looking at the air box there are two large (30mm) holes cut in the top so I can see the filter - I understand this is a common mod to help our bikes run better at higher revs. Thinking there have been some other mods I've taken a quick look at the jets etc but nothing to give me any indication here ie no marking or sizes. I'd like to bring things back to standard, so considering replacing all of the jets/needle with new (planning on Ducati OEM) but worried there may be other issues. Has anyone seen this type of airbox mod before and know if this is part of a larger set of upgrades made to help the bike run?...looking for any advice as bit stuck now - the dealer who completed the desmo service and initial carb clean has suggested getting it onto a Dyno to work through the issues, but I'm wondering if there are any next steps I could take before taking the Dyno approach?. Thanks for taking time to read this far, any thoughts very welcome Rick
Hi Rick Are you saying flat spot is cured now? Were the plugs a normal colour, and the correct ones? The extra holes in the airbox are very common and usually accompany a change to a Dynojet carb tuning kit, accompanied by a K&N air filter. The fact that you couldn't see any markings on the main needles (silvery in colour rather than straw?) might confirm this, and unless you have other evidence to work out which kit has been fitted, or a spare set with descriptions, then you might have to take to measuring them at the tip and at increments to determine what you have*, as there were at least 2 performance kits. My memory isn't good enough to quote chapter and verse now, but there are plenty on here that will help if you have further questions and if no-one can, then I can delve into my notes and can guarantee that you will get what you need, one way or another. You can also search this Forum (and others - Ducati.ms for example) for many threads on the subject, but it's often quicker to Google a few key words than use this search engine. *something I helped Alan with quite a few years ago when he first got his 750SS.
Hi Chris, the flat spot is not cured (yet hopefully)...the plugs were supplied by the service dealer so I'm 'assuming' they are correct, certainly when I put the replacement set in to get the bike going it fired up immediately and ran lovely. When I removed the plugs they were a filthy sooty/black colour hence why I think they are running rich. The air box mod should make the bike run lean ( I think) as there is more air flowing into the engine, but with the bike running so rich I wonder if there were other mods like the jets being 'upgraded'...which is why I'm posting in this forum in case someone may have heard of this modification before or may have an idea on the issue. It potters along at 2k quite happily, and once I ride through the choppy 2.5-3.5k revs into 4k and above its off like a rocket. thanks Rick
My suspicion based on rev range and sooty plugs is your needles and emulsion jets are worn as they do wear quickly in the BST carbs . So replace as planned an hopefully it will sort it fingers crossed.
It's possible that someone has fitted a Stage 2 Dynojet kit, and if so it could explain what's happening as ideally other engine mods ought to be done at the same time or else engine will be running at the rich end of the fuelling spectrum.
This is possible of course, but a full strip and examination would reveal the answer. It is only my experience, but after stripping and working on easily a couple of dozen pairs of Mikunis, I hardly ever came across the "rapid jet wear" phenomenon that gets quoted regularly on Forums, and even when i did find wear, the extra fuel that flowed as a result was never as much as the Stage 2 Dynojet set-up which is introduced by design on a standard engine and deemed acceptable.. Your theory can't be ruled out but, again, only my opinion, wear would have to be severe to produce a constant flat-spot similar to above.
Thanks Chris, would you know whats in a stage 2 kit?.....just looking at Macca's post just above, I'm going to get a new set of OEM needles and jets as a first start - would this replace the stage 2 mods if they have been applied? cheers Rick
Thanks Macca, 28k on the clock....feels like getting a new set of jets and needles would be a good first step to take...along with some gaff tape over the top of the 2x 30mm holes in the air box to seal that off ...at least we will know the carbs are back to standard....can always go the Dyno route following that if no impact. Thanks again, Rick
Thanks Chris, great feedback, I think the filter is standard Ducati, but will take a look into google at the kits to learn more. Feel that getting things back to standard with new needles and jets will also be a decent first start, thanks, Rick
I think that really is the best course of action as you will "kill 2 birds with 1 stone" because you will be replacing the Dynojet kit if fitted for a more consistent set (if it is Stage 2) and also removing the possibility of wear* - did you see any signs of this on your last stripdown? *see above post - possible but even if evident, still unlikely to be causing your problem (moo).
Big clue is the diaphragm return springs which are much lighter action on the Dynojet - needle slides can even occasionally jam as a result of fitment.
Exup was v. similar to "ours" but let's say an "easier to produce "version, I used to pinch parts off them, float bowls only had 2 screws! what I always robbed them of, was their remote cable for butterfly idle adjustment, sheer loooxery compared to std, neck-ache equiv on ours.
Will be in contact with Ducati first thing in the morning then Chris, Thanks. Didn't see anything major in the strip down, but feels like I should've been taking a better look now. Will share an update at the weekend once have replaced things - assuming Ducati spares are available for me , cheers Rick
https://www.allensperformance.co.uk/ Might be a better place for carb spares & also consider looking at /replacement of main jets as dynojet ones are different to oem so will probably not be correct for stock needles/emulsions. Luckily it only has 2of each but sit down before looking at prices. I once priced up internals refresh for 4 VM flatslides on my old Gsxr750 & it was near the price of 4 new RS flatside carbs.
