Isn't that blue wire the earth wire for the reg/rec.

Also why would the split fuel "Y" be a possible cause for running on 1 cylinder. Sure for running out of fuel but the float bowl isn't segregated between carb throats is it (I haven't pulled one apart for years), hence I would not expect only one throat and therefore cylinder to have fuel when the other doesn't.

Sorry fellas, maybe I wasn't clear in my original post.

The bike started and ran fine initially when I went to get petrol. When I restarted it after filling up, it immediately ran on one cylinder and continued to do so on the two miles home.
My first thought was to check the spark plugs. I removed both, cleaned them up and refitted them but no change. I swapped them over and still only one cylinder ran. I removed the HT lead from the back cylinder and the bike cut out so I refitted it and removed the front one but the bike kept running - which pointed to the front cylinder being the one that wasn't running.
I could see that both coils were looking a little bit sad and so decided to remove the tank so that I could get to them and give the connectors a clean up. It wasn't until I started to lift the tank (after turning the tap off and disconnecting the hose to the carb) that I could smell fuel. Initially I thought it was maybe residue fuel from the line so put the tank back down and checked but could see petrol all over the rear cylinder and starting to pool under the bike. I quickly removed the tank and that's when I noticed the split Y joint. I suspect this wasn't split, at least to the degree it is in the picture until I removed the tank.
I redirected my attention to the coils again and so disconnected the battery terminals and I was intending to lift the battery out, but it's such a tight bloody fit I had to try and grip it at the bottom and push it out, rather than lift it from the top, but I couldn't get it to budge it's wedged in so tight.
I knelt down by the left hand side to see if something was obstructing the battery and thats when I saw that a bolt on the back of the rectifier was loose. It's on this bolt that the blue/black lead that runs to the negative terminal on the battery was sitting, but because the bolt was loose the lead wasn't held firmly between the head of the bolt and the rectifier.

I've done my best not to make it seem like an April's fool but my mechanical knowledge is less than zero.

Hi Fester,

It's a simple KISS logic principle.

Reading TheDuctor's opening post, it was running fine one assumes with little fuel load, got a full tank increased the pressure with the fuel load and pouring more out the break than in, and he wouldn't have known about the split til pulling the tank/side panels off, and possible making the break worse pulling off the fuel lines.

I use the fuel pump on mine to drain my tank every now and again to put in fresh fuel for track days and there is a fair drop in flow and pressure as the fuel load decreases, bit like me but that's just old age .

I know nothing about the webber setup, but knowing my Sport's setup with 2 Keihin's that split in the Y piece would kill the front cylinder on mine through starvation.

TheDuctor doesn't state whether there was an issue before, or if it has the webber or 2 carb's, the reg/rec shouldn't cut one or the other cylinder out, the system just won't charge I thought, sure I'll be told otherwise.

Again I bring it all back to the KISS principle.

Cheers

Peter

Was about to post this when TheDuctor clarified a bit more, I still say dry everything off and again start with the Y, then go from there, public apologies for taking the piss.

Cheers Peter, apology humbly accepted.

I've never had any issues before. The bike was very low on fuel - the fuel warning light was on.

It does have the original Webber set-up mind.

Ok, you need to fix the fuel line and re fit that wire . lets assume for the moment that the carb is ok , you have established that its the front pot that's not working , 1st thing to do would be to check that there is spark, remove both plugs ( keeping them separate ), fit the front (hor) plug to its lead and rest plug on frame or engine and hit the starter ( after checking bike is in neutral..................you wouldn't be the 1st ) and look for a nice blue spark ( and there is a wee ,possibly very humourus trap here for newbies .............. DONT place the spark plug anywhere near the plug hole.......... especially with your face in nice and close because as you crank the engine fuel mix will be pumped thru the engine and out the plug hole ........right where the hopefully sparking plug is .......last time I seen this happen it singed his hair , mo , sidies everything except for his eyebrows as he wears glasses ..... Fuck he looked funny...) anyhow , it there is no spark try another plug , like maybe the rear one as we know this works and check for spark again , someone else has already mentioned swapping the cdi units and pick up's over ( I think these things have the Koukosan ignition ) and see if its still the front pot that's not going , the idea being that if the fault ( 1 pot not working ) changes to the other pot when you swap a component over then its probly that component that's faulty . Apart from checking all the plugs are properly plugged in , and that there is power getting to both coils ..........everything else gets a bit more complicated.
Hamish

As Hamish has said check the spark situation. If that is fine then maybe a blockage on one side of the carb given it was low on fuel. Could have sacked something into a jet for the front pot.

Oh no cdi's to swap on this one. The 900 runs the Digiplex same as the Paso.

Thanks chaps. I knew owning an older Ducati would involve getting my hands dirty and I must say that I'm quite enjoying it. I've ordered new fuel hose (8mm or 5/16"_ internal diameter), I've gone for the nylon style hose to keep it looking original as the bike is totally standard, even down to the original toolkit under the seat. And a new barbed Y joint, all in just over ten quid, so no major damage to the pocket. I was reading through the good old Haynes manual last night and it says not to start the bike without a spark plug being in as it can cause major damage to the ignition though. Am I ok to go ahead testing the spark plug against the engine (away from the open plug hole - I've little enough hair as it is without doing a Michael Jackson)?

Fester, had a look at the parts diagram for the Webber for my own understanding of what you wrote about the Y piece, and get where your coming from, possible blocked jet and sitting for so long is logical, if it isn't the problem, move on to the next step.

And no it shouldn't upset or short the ignition so long as it is earthed so to speak against the head or cylinder while the ignition is on, what Hamish suggested is a practical, century old nearly, tried and proven method to check spark, and an old school tuning method as well on aircooled BMW's i.e. proper one's, pull a plug lead and it should run for 4 or 5 seconds on 1, yes I'am that old

Had to do a spark test on my '88 BMW the other day, it wouldn't start, turned out to be a simple I flooded it trying to start it issue and easy fix but that was one of the simple checks as part of the elimination process.

Michael who..................

Cheers

Himself

The other tried and true method of testing the spark is to hold onto the plug, that way there is no possibility of it igniting any loose fuel from the cylinder. Father in law and I used to get the mother in law and wife to help us test the spark on his old Ariels. They did it more times than I think they would care to admit.

I had an R80 for a while ( slew a few myths ) and read of this method in the book ( Haynes I think ) and I did it this way and did it using vacuum gauges , and the plug lead off method is just as good and a whole lot less mucking round . I dunno if the irregular firing order of the duke would lend itself to this method tho

you could just tell every one its a supermono prototype with a horizontal redundant cyl

When you first fired it up, was it with the fuel that was in the tnk after sitting for 12 months, or did you drain that all out, rinsed the fuel tank, then put a litre or 2 in to get to the Fuel Station? If you went with the 12 month old fuel, fair bet the fuel filter is clogged with all sorts of mud, grit, rust, last years Christmas dinner and what ever else the kids have stuck in there over the last 12 months. Change the fuel filter along with all the hoses and clamps. It could be the cause of low fuel pressure etc. Does the 906 have in tank fuel lines? If it does and you change them, make sure you use the correct rated fuel line. Its SAE R10 from memory? Anything else will disolve in about 6 months.

Cheers.

Nick.

Quick update chaps. Finally found the time to replace the Y joint, the fuel lines. Bike started up and ran fine on full choke, but as soon as choke is knocked off it goes back to running on one cylinder. Never had this trouble with jap crap!

I don`t like repeating myself but I guess you measured voltage at the coils and checked carb synchronization ...

No not yet. Only just got round to doing the fuel lines and was hoping against hope that was the ptoblem. It's booked in to have the swingarm removed and welded next week so I'll get the running looked at the same time.