900ss Carburation

I have a 1994 900ss with mikuni carbs and a stage 1 dynajet kit. When I got the bike it would idle roughly and its slow speed performance was lumpy whilst its acceleration was rapid after a cough when the throttle was opened rapidly but since it was cheap bought it any way. I was told the problem could be carb icing so i fitted a heater kit I got off ebay. This helped with the idle but nothing else, and when I checked the spark on each plug using a home made tester it is thin and yellow / blue rather than a fat blue. The ignition coil primary resistance readings are within spec but the secondries are 18k ohms instead of around 11k advised in the manual the leads checked out OK (could this be a problem - a local mechanic thinks not). I have been advised it may need the carbs overhauling but cannot find a supplier of such a kit who doesn’t want more than a set of new carbs costs. This brings me to the point that I have read a few articles that recommend a change to Keihin flatslides as they are supposed to “transform the bike” but find the new price a bit too stiff - does any one know of a good set of second hand ones or a supplier of mikuni kits or can help in any way because a part from this issue the bike is great .

Hi Stephen,

Welcome to the fold and glad you like the bike. I’ve got a '94 900ss too and I love it to bits. My carbs have been modded to run a Stage 2 Dynojet kit with a K&N air filter and modded airbox and I find that it runs smoother and stronger than with the standard set up (I also have carbon fibre end cans fitted). Before you invest £600 or so on flat slides I’d be tempted to try and resolve the running issues you currently have. The Mikunis won’t develop ultimate power but they should allow the bike to run well throughout the rev range. Changing them won’t necessarily solve your problem.

Has the bike been stood for a period of time? If so I would recommend that you get the carbs ultrasonically cleaned to remove any deposits that the stale fuel may have left. I would also check the diaphragms while you’re at it or just replace them as they are 16+ years old by now and may well have holes in them even if they look ok. The Mikunis are also fitted to the Yamaha TRX850 so your local friendly Yamaha dealer may well have parts in stock. If you have access to vacuum gauges then this should be your next step, if not say hello to your friendly Ducati dealer and goodbye to some wedge. It is notoriously fiddly to adjust these carbs but it can be done with a long shafted screwdriver, preferably with a small torch taped to it so you can see what you’re doing.

With fresh fuel in the tank and new, correctly gapped plugs it should start easily and run well. You don’t say where you live but if you’re still having problems and you’re reasonably local to me (Weymouth, Dorset) then give me a shout and you can bring it round. These are inherently simple bikes to work on and it should be straightforward enough to get it running well. I would be surprised if you will find a set of secondhand Keihins because they work so well that no-one ever seems to swap them back.



Thanks for that chris - I shall give those suggestions a try in the next few days. The yamaha connection is useful as an alternative source of spares. I live in Tynemouth near Newcastle so a trip to your place would be a large journey

On a different, but related subject.
I’m told that a pair of Mikuni’s from a 900SS should be pretty much a bolt-on fit to the 906 Paso.
If so (and I’d welcome any confirmation, or burst my think bubble) does anyone know of a set going for a reasonable price to an impoverished webmaster :question:

No. But I have done it! I fitted a set of TDM850 carbs to a paso. Just needed to pay Bains brothers to set them up with a dyno stage 2 kit and they worked fine! It was a long time ago now, but I seem to remember the hardest part of the conversion was getting the right manifolds from a 900ss