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!.
Chris the small bore carb bowl bleeders don’t go the the vapour box, they just go “overboard” towards the bottom of the engine as with most other bikes, if I understand Al’s post correctly the single carb bleeder tube that does go the the vapour box is I believe just an air/vapour vent to prevent a pressure build up in the carbs.
the confusion came from the red arrows on the diagram in post #20 - that's why I called them 'small bore' pipes.. as you were then..
The carb bowl bleeders as you call them are also the float bowl overflow tubes - for example if the float gets stuck open; or if the fuel height is too high, you will see why they are 'overflow'. They will also drip (or run) if the tank pressure gets too much when the breather valve doesn't release when it should (a common occurrence) or when the tank has been brimmed and then left on a rear paddock stand although in that case it is more likely to drip from the tank breather hose. I extended the bottom of those tubes and clipped them to the rear edge of the fairing lower, otherwise they would drip just inside the fairing at the bottom and eventually make a mess of the paint - mine were turned outwards so that they didn't drip (or run) near the chain or rear tyre.
Great, thanks Al, I had already ordered the carb to intake clam but couldn’t find any big enough for the carb to airbox joint so thanks for the link I’ll order some.
As I said Al, in reality this rarely happens and the majority of fuel ends up dribbling into the crankcase via the inlet manifold. This happens on so many similar setups and maybe it’s more likely on ours because of the inclination of the carburettor bodies.
I always hate it when I’m searching threads for answers to any particular issue that I’m trying to fix and all of a sudden the thread which I’m getting good info from just ends without the OP saying if the fix he/she was trying worked, so in case anyone looks through this one in the future here is a round up so far. 1. The carb to inlet clamps I bought on eBay are good quality £5.40 for the set of four delivered, here’s the link https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/260724681596 I bought the slightly larger clamps for the airbox to carb joints from the link that Arquebus posted, again they are good quality. 2. The step remains on the slide guide, I’m convinced that the guide itself has deformed with age/heat, when I temporarily swapped the slide guide from the other carb it fitted without a step, I doubt it affects running but I will purchase a replacement soon. I finally had time today to put the fairings etc back on, hopefully it will not rain tomorrow so I will get out for a test ride, during the strip I found some of the jets were partially blocked, there was a lot of dirt around the diaphragms (from the breathers I assume), no major issues really, so now everything is cleaned and float heights checked it’s fingers crossed for a good run, the bike ran reasonably before but snapping the throttle open could result in a “stutter”, I’m hoping this was down to partially blocked jets or the carb inlet clamp being loose, if the “stutter “ Is still there it’s back to the drawing board !.
Good news, running perfectly!, no hesitation in revs or stutter at all, just been out for a couple of hours giving it the beans and all is well, so either it was the partially blocked jets or it was drawing air at the intake rubber where the clamp was loose, I was forgetting just how good these bikes are! , totally addictive sound track, effortless acceleration, someone on this forum once described them as feeling “as though all friction has been removed from the motor” I know what they meant by that, wonderful machine!. Now as Columbo would say “there’s just one more thing”, I got fuel coming out of the fuel tank breather pipe, second time in recent weeks, I had just filled up but I don’t think I filled it any higher than I have over the last 3 years of ownership, I pulled the breather hose off the tank and blew down it, there was resistance when I blew (it allowed some air through but had to blow hard) then sucked and there was no resistance so I think the valve is working, maybe I am just overfilling?
Umm, isn’t the idea that it lets air in to avoid a vacuum in the tank but doesn’t let it out? Valve wrong way round?
I’ve started the bike quite a few times now since cleaning the carbs, it starts so readily now it’s almost worrying , previously the engine would need to turn over 3 or 4 times (one press on the button but turning over 3 or 4 times) before it caught, now it’s pretty much instantaneous!, hot or cold (with the choke on when cold of course), I mention it because you see a lot of threads blaming battery leads/earths for difficult starting, but it’s worth bearing in mind that if the carburation is off the bike will be more difficult to start.
