Taking my carbs off to clean them I noticed that one of the plastic carb slide guides wasn’t flush with the carb body, this is only on the RH carb, on the LH carb it’s perfectly flush, looks a big step in the photo but is less than 0.5mm, so I took it out, cleaned the guide and the housing, it still won’t sit flush, there is a circular feature on the slide guide that fits into a recess in the bottom of the carb body, I think that this is what’s stopping the slide guide going down that extra 0.5mm, any thoughts would be appreciated , thanks Mark. (The circular feature on the guide is the one at the very bottom of the 3rd photo).
Thanks for the replies, I’ll have a play around with the slide guide tomorrow (that said it’s good weather tomorrow and there’s bikes to ride ) Does anyone know the correct float height?, NRP said they’d write it on the gasket set receipt but forgot to do so, Haynes says take it to a dealer and tinternet says 12,13 & 14mm!
I’ve never known one to be normally unseated by half a millimetre Sev - It’s quite a precision assembly? I would tend to think the brass main jet was not fully seated or there was a burr or obstruction on the plastic locating boss or in the recess in which it sits.
Hi Chris, both the seat and slide guide look perfect, also cleaned them thoroughly so it’s not debris, I didn’t have much time earlier but my initial impression is that the circular boss on the guide is too big for the recess in the carb body, too large diameter, it could be clash of tolerances, I’ll have a better look at it tomorrow, it might just be a matter of reducing the dia by a few thou using a fine grit paper, if that’s the case it must have been like from new.
When I had an SS, the accepted height was 14mm. However, @Arquebus on here says that's all wrong. Hopefully, he'll pick this up and give you his guidance.
I wouldn't go reducing or sanding Mark - it really shouldn't need that, they are finely toleranced and matched when initially assembled and it should be a lovely snug/slide fit - you don't want it to be loose. The only two things (apart from already mentioned) is that plastic got distorted by heat/solvent etc or the plastic retainer and/or the brass jet don't belong with that carb body. There were many derivatives of that Mikuni and I know there are subtle differences between Ducati fitment and Yamaha FZR that make some parts incompatible for starters. Re: float height - all details are available online with a bit of patience. I've never had a problem setting up in the past although it might take a few goes particularly if engine modded - this is par for the course and still far easier on a Ducati than a multi Dellorto/Weber equipped car.
Hi Chris, what I’ll do today is temporarily swap the slide guide from the other carb , if it sits fully home then it’s a good clue that there is an issue with the slide that was initially in that position, I don’t want to bank too much on the boss being issue at present but the reason that I suspect it is that I can feel the slide guide going tight as I push it home and when I push it out it takes a bit of pressure to do so and then it suddenly “pings” out, like it’s jammed, looking at the boss when it’s out I can see a witness mark around the circumference of the boss as though the recess is “grabbing” the plastic boss, if the other slide fits correctly I can get my vernier on the bosses to see if they are the same, point taken on not removing too much material from the boss of course (hopefully it won’t be necessary at all) , I have searched at length online for the nominal float height but there are too many “convincing” alternatives!, I’ll PM Arqebus to see if he can shed any light on it, anyway out for a ride at mo so that’s for later, thanks again all for the advice.
I spoke to Al, he was very helpful, float height should be 12mm on the larger side of the float (the non diamond shaped side) , that’s what mine were set to so no adjustments needed, regarding the step, I can only think it’s due to the slide guide being slightly deformed with age, if I leave off the O ring it goes away, tried with the old O ring and the one in the rebuild kit, no O ring no step, O ring fitted there’s a step, so decided to leave the O ring in place and put up with the step, the bike was running ok but I’ll get a replacement slide guide at some point, thanks for you help and advice all.
Put the carbs back on today, fired it up, ran beautifully for a couple of minutes then started backfiring, I had noticed that one of the clamps that hold the carbs on wasn’t clamping so suspected it was drawing air in at the joint, (the last person to work on the bike obviously wasn’t bothered by that, or that there were no clamps at all on the air box rubbers along with a lot of other really poor workmanship that I’ve discovered along the way but along with them denting one of my silencers that’s another story) anyway I then remembered that I hadn’t set the mixture screws , set them to where they had been previously and no more backfire, phew!, couldn’t go for a ride because it started raining but I’m expecting an improvement as some of the jets were partially blocked, now I need some new clamps, the bands are narrower than ordinary jubilee clips (9mm?) does anyone know a good source?, cheers Mark.
You might be better off trying to source the original clamps either new or secondhand as they are a bit special. I take it yours are damaged? People often overtighten them which results in damage to the rubber coupling rather than damage to the clamp.
Hi Chris, yes it’s obviously been over tightened in the past, with light pressure it will hold but any more than that it just “pings” and loses it’s clamping force, i.e. the slots in the band are deformed and the worm screw just slips, it’s not even beginning to squeeze the rubber at this point so a replacement is required, I’ll probably have to pay Ducati 20 milionty pounds for one , as a temporary measure I’ve used zip ties on the carb to air box rubbers where there were no clamps at all but again I’ll probably have to get new from Ducati unless I get lucky and find a used set on eBay, I’ll have a search, cheers.
slight gamble, but these might be ok? https://www.ebay.co.uk/itm/DUCATI-M...033399?hash=item2aa54ed4f7:g:JEEAAOSwsMpZkCg4 could do with some more pics - looks like at least one is odd but looks to be stainless and the correct width.
Thanks Chris, I’ll have to check the inlet size for the 696, when I searched earlier I found nothing for 900ss but lots of stainless carb clamps 8 & 9mm band width for Suzuki, Kawasaki etc, I just need to check what diameters I need for the air box to carb and carb to inlet tomorrow, so between the above alternatives I’m sure I’ll get something, on another point you don’t happen to know where the carb overflow union pipe should terminate do you?, Haynes doesn’t show it, I mean the pipe that comes off the black union in the photo, from its length it looks as though it should go to the black triangular box that the carb top breathers go to, but I can’t imagine why an overflow union pipe would go there?.
Thanks Jon, so it does go to the black box, there is a “spigot” for it to mount onto on the top fwd corner of the box (ref photo), it wasn’t fitted to it as received back from its recent trip to the Ducati workshop (but given the amount of issues with the work they did that was no clue I suppose!) so when I refitted the carbs yesterday and looked for somewhere for the end of the pipe logic made it hard to believe it would go to a breather box!, I am as surprised as Chris! , maybe in the worse case scenario it would only ever see a few drips and would go there to evaporate? But if it ever did carry a large amount of fuel to the box it would then drip out of the bottom of the box onto the alternator cover!?!. Ref the float bowl drains that you referred to Chris, on my CR750 Honda SOHC when I had a float issue some of the fuel went down the drain pipe and overboard as designed but an equal amount ran out of the back of the carbs and all over the crank case, so yes they don’t cope very well
Thanks Al, yes that’s the one “Carb bleeder tube”, still seems an odd thing to do with a pipe that potentially carries fuel, but I’m sure Ducati knew what they were doing! :/
In my communications with Ducati Italy, it seems that the triangular breather box is in fact a flame trap for the two thick and one thin breathers. In theory, the thin one allows fumes / air to be pushed out by incoming fuel (so it can get into the carbs) but the two very thin overflow pipes are what deal with fuel level too high for whatever reason.
That makes more sense, so the Haynes manual names it incorrectly as an “overflow” , not unlike Haynes to get it wrong!.
