My query is for the correct setting of the carburettor pilot jets on my 1992 Ducati 750 Supersport and is required because they were seized in the carburettors and the original settings could not be saved. The two manuals I have (large multi-language Ducati and Haynes) only say that on dismantling the jets should be screwed in and the number of turns noted but this does not assist in this case. Any guidance would be much appreciated.
The pilot (idle) jets are fixed, so I'm thinking you mean the idle mixture screws. Turn them clockwise until they slightly bottom out and then turn them out around 2 & 1/2 turns, to obtain a rough baseline. They then need to be set with the engine running, with a slightly fast idle. Turn them out or in until the engine speed is at its highest and engine seems the most responsive. Be prepared for a range from at little as 1 & 1/2 turns to 3 & 1/2 turns out, although it'll probably be closer to the latter. Don't be surprised if each carb is slightly different in its final setting. Turning in will lean off the air/fuel mixture and vice versa. Try and avoid letting the bike overheat. If you have a floor standing fan you can place it in front of the bike to help.
Thank you for your useful reply and the setting I am trying to confirm is described as the "pilot screw" in the Haynes manual and is below the "the pilot screw plug" which must first be removed. The Haynes Hint is "to record the pilot screw's current setting, turn the screw in until it seats lightly, counting the number of of turns" using this to return it to it's previous position on reassembly. It is necessary to remove and dismantle the carburettors to access and adjust these. For clarification the carbs are Mikuni BDST 38mm CV and apologies for any previous ambiguity. However, I recall that 2 & 1/2 turns has been previously mentioned so this may prove to be a reasonable base setting.
The idle mixture screw has a fine point and a spring that sits below the thread. If the component you're referring doesn't match that description, would you be able to take a picture (including its location on the carb) and upload it for reference? The Japanese use the term 'pilot' in place of idle, which can get confusing. With the idle mixture screw there is no standard setting because its position is dependent on the volume of air through the venturi. 2 & 1/2 turns out is a rough baseline but is only a starting point. The screw should be accessible with the carbs mounted in position though.
Attached photos from Haynes manual show the pilot screw plug with the float bowl removed, hope this helps identifying it.
Yes, that's the idle mixture screw. Even though it's shown in the picture with the float bowl off, it's accessible externally and would normally be covered by a green plug.
My mistake the pilot screw plug is accessible with the float bowl fitted and so could be removed and presumably the actual pilot jet adjusted but is on the bottom. I will initially set to pilot jets to 2 & 1/2 turns and although it may be a bit awkward I hopefully will be able to adjust them if necessary. We may have been talking about two different types of carburettor with mine being Constant Velocity (CV) type with pilot jet adjustment from below and perhaps you were thinking of normal slide type with adjustment on the side. Thank you for your help and interest with my unknown setting problem, constructive comment and advice is always appreciated.
Hopefully I've been of some help and you'll be able to get your bike running well. You're right to point out the difference in location though. They're not that accessible on the CV Mikunis whereas with standard slide type Dellortos, the screws are right in front of you. I prefer the latter!
