Just had a go at balancing carbs on my 93 900SS, has always run very rough below 45mph, surging and hunting, nightmare. Will check on the road next week to see if I have improved running. Question is, I have mixture screws at 3.5 turns from closed cos I read somewhere that is where they should be. Bike smells as if running rich, plugs a bit black, sooty. So I want to lean out. Do I go to 3.25 turns or 3.75 turns. Reckon it should be 3.25 or even just 3.0. Any thoughts? Thanks Andrew
It's difficult to diagnose what the cause of your problem is..........but... Many SSssss will run 'rough' at low revs.......surging and hunting are two different things....... The problem you are looking at is that the low revs running is all part of the pilot circuit.........that involves the fuel height in the float bowls as well as the pilot screws........if you want to lean out, try 3 turns out. But...... at higher revs and under what I would call 'performance' load, I would look at the main needle position. I can't suggest much else unless I know if you have a Dynojet kit fitted and what your airbox and zorst set-ups are.
Thanks will give 3 turns a try. erm what is zorst, thought it was a German sausage? But seriously I don't have a dynojet and have a standard airbox/filter set up. I did try a K & N air filter ages ago but seem to remember it made it worse.
OK...'Exhaust'..........happier now? How do you know you don't have a Dynojet kit in there?...............X-ray eyes.............?? You won't know until you have a look inside the carbs..........have you had a look?
Ah got it! I have Chris Clarke Racing carbon cans. 2 years ago I bought a set of replacement carbs off ebay, I made a decent set by taking best bits from both, checked all jets, needles etc to factory spec, then put bike back together. Problem at low revs was much the same but its taken me 2 years to finally have a go at balancing carbs. Am happy to just fiddle with balance, and now use your knowledge thanks to lean out mixture.
If you have standard airbox and it still runs a bit rich (which you won't really know from the plugs until you have done a good long blast on the bike) you can try running it without the airbox trumpets........that will also lean it off a bit. The standard pilot screw setting is approx 2.5 - 2.75 turns out; but whatever you eventually use, don't expect the two to be identical.
The standard settings for the SS are not necessarily the best for smooth, powerful running. Ducati were struggling to get the bikes past emission regs and the standard settings are mainly about that. If you read the workshop manual, it hints strongly at this, without being too specific and recommends you use different settings for optimum performance. Alternative needles and jets from Dynojet or Factory Pro are designed for best performance and that is likely to include economy as well. I used Morgantune gauges for balancing my carbs - highly recommended. Morgan Carbtune - carburetor synchronizer for balancing motorcycle carbs
always worth remembering that the idle mixture screw has a fuel circuit so closing screw will shut fuel off/make idle mixture weaker. Engine cc/jet and or needle set up/air filter/engine tune/carburrettor wear and even climate will dictate settings for these screws and can easily vary from 1.5 to 4.5 turns out from fully closed.
Ok food for thought thanks. Not too bothered about performance or economy, just smooth throttle response around town would be nice. How do you fine tune idle mixture screws?
If you want smooth throttle response, get a jet kit, get a coil kit, get a carb-tune and drop the gearing. Dropping to 14 teeth at the front is a quick, easy, cheap fix. Setting up mixture screws is as much an art as a science. Using a CO meter to get the mixture about right, then using the carbtune to balance the screws, then recheck the CO etc could be a reasonable plan.
