Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > Supersports: SS / SuperSport / Supersport 950 > spark plugs

[phill]

advice to a newbie please- i have a 91 900ss (white frame model) with 40k on the clock. went for a run on sunday (120 miles) and checked the plugs and they were black. I noticed that they are ngk dcpr9ea9, the equivelant of the recommended plugs wolud be dcpr8e. Would the colder plugs i'm using cause them to be a bit sooty?. Also she backfires a bit through the left exhaust on the overun when cold (1st 5 miles say) - is this normal? Bike has just had the valves and belts done at Veloce in norfolk

[Shazaam!]

A hotter plug will help somewhat in burning-off deposits but a sooty plug is always a result of an over-rich fuel condition. It could be just a dirty air filter.

Check the left exhaust silencer for an air leak from a poor fit to the exhaust pipe (that closes up as it gets hot.) An air leak will add combustion air to any unburned fuel in the exhaust system causing it to ignite on hot parts and backfire. During warm-up, more fuel is added so there's always more unburned fuel passing through.

[Derek]

In addition to Shazaams comments I'd consider replacing the emulsion tubes (needle jets). If they've never been changed at 40K they will be shot by now. Over a period of time the needles wear a groove in the jets turning them oval. Symptoms are a rich mixture and lumpy low speed running. I changed mine at 21K and it transformed the bike's behaviour at low speeds and around town, also picking up much more cleanly.

[phill]

cheers guys - i checked tha air filter and it looks clean with no dirt around the carb chokes. Re the jets, i'll check all the paper work i got with the bike and the carbs were suposedly stripped and cleaned last summer, but the syptome you describe seem about right - on an open throttle thought she pulls well after a flatspot at 5k.

[phill]

just another thought, can the needle jets be accessed with the carbs in situ after removing the float bowel, or do they need to come off?

[Derek]

With the float bowls off you would be able to see the needle jets (just) but I doubt if you could assess the state of wear. We're only talking about a few thou and it is hard to see with the naked eye. The jets come out from the top and the carbs will need to come off to to do it. When removing the carb tops watch out for the tiny O-ring at the air passage at the side, it is easily lost. Also be careful with the O-rings on the main jets, they tear easily. Lubricate them with a very light smear of vaseline or silicone grease when installing.

[Iconic944ss]

Not sure if this NGK link will work....

http://www.ngkcat.co.uk/CatalogueDis...tandard%20plug

sorry - it does not....just start a new search for Ducati....the Iridium plugs also get a mention....

Carbs....

Check out the 'Mikuni/Keihin' link on the left of the page...

http://www.factorypro.com/products/n...20rebuild.html

[Edited on 17-4-2004 by Iconic944ss]

[phill]

Thansk for the info guys, what a good forum. I changed to an 8 grade plug and it is a better colour, (dark brown as opposed to black) and the back firing was an interesting one. The valve shims were done recently and this must have thrown the carbs out of balance - quick check with a vac gauge and one was way out. Rebalance and she runs lots better and has lost most of the low speed snatchiness