900SS Ignition Project

Serious Black

Serious Black

Active member
I´m going over the 93 900SS Ive just bought and was surprised by just how poorly the thing ran bellow 3000rpm even after pulling the carbs to bits and shacking out the Gremlins. It behaves just like my Trtion with race cams but with a horrible transmission snatch thrown in to make things even more fun.

To cut a long story short, I noticed when I pulled the airbox out that the ignition pick up wires ran awfully close to the coils and HT leads. Ive read that it is not unknown for these things to eat ignion pick up coils and black boxes so I was wondering if this might be why. Ive had problems before with Boyer Brandsen ignitions picking up interference and causing rough running, especially at low revs.

I decided to try the same trick I used on the Boyer igniton to cure the problem. This mean screening the pick-up wires. This was done by wrapping the leads in thin aluminium foil (I used stuff meant for air conitioning duct, sticky on one side) and then wrapping the end of a copper wire round the tape and earthing it to the frame earth. The foil was then wrapped with insulating tape.

The snatching has gone now and the bike feels smoother although it still behaves like an off-cam sports bike bellow 3000. My arse dynomometer says it feels a touch quicker from low revs but it´s in dire need of re-calibration after years of Ural and Dnepr outfits. Hope this may be of use to someone.
 
Went out for a long run tonight and noticed the engine is a lot better behaved on the over run too, much sweeter. I had a talk with a mate who has more experience of electronics than I have and he siad the earth wire to the frame may be un-necessary so I´ll disconnect mine and see if I notice any difference. We decided that wrapping the Kokusan boxes in foil is probably also a good idea. Taking the whole thing to extremes, as you do, twisting the wires (3 -5 turns per inch?) will also help keep the trigger pulse to the black box clean.

While on the subject of the Kokusan black boxes, I noticed that they are externally identical to some of those available for Pitbike motors These retail at about 10 - 15 quid. Wouldn´t it be nice if they were a direct replacement? Might try it. If they are compatible the there are also programmeable boxes available for about 20 quid each. They have three different advance curves. Would it be nice if they worked too! I´ve got some wiring diagrams on my laptop that I´ll have a shufty at and compare to see if they are at least electrically so.
 
Serious Black said:
While on the subject of the Kokusan black boxes, I noticed that they are externally identical to some of those available for Pitbike motors These retail at about 10 - 15 quid. Wouldn´t it be nice if they were a direct replacement? Might try it. If they are compatible the there are also programmeable boxes available for about 20 quid each. They have three different advance curves. Would it be nice if they worked too! I´ve got some wiring diagrams on my laptop that I´ll have a shufty at and compare to see if they are at least electrically so.
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Interesting... keep us posted :cool:
 
Very interesting. I would think that the foil screen should definitely be earthed to the bike and why not replace it with the copper screen removed from a length of video cable? That would be far easier to fit, much stronger and look better, and once fitted you could paint it black if you liked or fit heatshrink or plastic sheathing over it. Alternatively you could replace the entire pick up wire with a length of screened twisted pair cable.
The Pitbike ignition boxes may look the same but I'll bet the ignition advance is entirely different and may not do your Ducati any good. Have you considered the Ignitech system?
 
Took some time tonight to research the Pitbike boxes - they won´t work. Oh well, nice try. I didn´t have access to the wire braiding so I used what I had. STP cable uses aluminium foil so I thought it would be fine. Replacing the whole wire with STP (Shielded, Twisted Pair) might be a very good idea.

If my Kokusan boxes die or I can´t find another way to cure the irritating stumble JUST as I come of the idle jet at about 3000rpm then I´ll probably invest in the Igitech system. The main power cable to the relay and all the ignition wires will be getting replaced by something a little beefier in the winter. I´ve seen articles on fitting Dyna coils and I reckon they are a waste without doing something about the wiring first. I´ve already run a separate relay arrangement to power the lights directly from the battery. Now I can see where the road is at night. This has the secondary benefit of relieving the rest of the loom of 4 or 5amps. I´m lucky here in Norway ´cos we have an shop called Biltema that sells an uprated loom off the shelf for older cars. They make Halfords look a real M Mouse outfit.

Anybody got any ideas on how to cure the stumble?
 
Thanks Derek, ordered from the States. It will be nice to ride around the town in a relatively civilised manner, especially as my short period as stand-in thunder god is about to end. The carbon pots are coming of tonight for re-packing.
 
Might aswell round this thread off with the results. I had already ordered a set of second hand carbs from the UK. These were off a 94 bike with the carb heating ( can anybody post a pic on how to plumb it in? Which cylinder?) and had less miles. They also had a stage one Dynojet kit fitted! I fitted the Factory Pro needle jet to these carbs and the bike ran very sweet after I fixed a glitch with one of the enrichment plungers not being engaged in the little fork that pulls it out. It still doesn't like going much below 3000rpm but it doesn't cough and snatch anymore and mini roundabouts are a bit more fun.

I put the plug gaps to 0.9mm. I'm using the standard silencers, K 6N filter and I've removed the trumpets from the airbox. The dynojet kit is set up as per the dynojet instructions with a 128 main jet. I've wound the bike up a couple of times and there may be a need for further work. Time to find the local dynomometer guru.........
 
I managed to find this on my travels :)

16a.gif


Suggestions, fuel filter change and line flush, full carb overhaul, get balance as good as possible, Iridium Plugs and a Bigger back sprocket....

Good luck - Frank
 
iconic944ss said:
I managed to find this on my travels :)

[qimg]http://www.ne.jp/asahi/ducati/toolbox/D-data/900ss/16a.gif[/qimg]

Suggestions, fuel filter change and line flush, full carb overhaul, get balance as good as possible, Iridium Plugs and a Bigger back sprocket....

Good luck - Frank
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Also, set the float heights to 14mm and the idle screws at 3.5 turns out for starters. You can fine tune them once you see how it behaves on the road.
 
Interference

Sorry to tack on to your post but I thought I would share something, a few years ago I had to look at a Renault with Electronic Auto Transmission. The owner said it had run ok until it's last service since when it had developed problems with the transmission shifting or not as it was supposed to? After lots of fault finding I traced it to the spark plugs! They were the wrong application and non resistor. After replacing with the correct one's the transmission returned to normal operation! The Transmission Control Unit was obviously suffering from interference from the spark plugs!
 
Thanks Frank, that is exactly the picture I've been trying to find. It also shows some bits I'm missing.

Derek, Thanks for that info. The float height adjustment will have to wait a little while now as I want to make the most of the tail end of the riding season here. The idle screws are at 2 1/2 and 2 3/4 turns at the moment as opposed to 2 turns in the Dynojet instructions. The idle is nicer and the clutch rattles less. I have to take a closer look at the ignition timing some time too. It feels OK. I did some time as a motorcycle mechanic when I got here and the shop got the Ducati franchise. I only did a couple of first services before I went off to the North Sea to fly ROVs but one was a 900SS. The timing from the factory was MILES out. Incidentally any jetting info for the carb model would be welcome , especially for mods on bikes using standard silencers.

Richard, I've seen some odd things myself when diagnosing faults. I had a digital multi-meter beside a Boyer electronic igniton once and it gave all sorts of strange reading until we moved it.

It's now time to try and set up the handling. Never had so much to play with before. I've set it to the factory settings and it feels nicer already. Need to quicken the steering though.
 
I suppose I should tack this on here. I should RT right FM! I downloaded the Dynojet instructions from the internet and read them. They are for the US model and my kit is for the European model which I didn't notice and explains the slightly bigger main jet. The European kit is also for use with the top removed from the airbox which I also hadn't noticed. I had tried it without the air horns and it ran better and sounded gorgeous. The top is now done so I'm hoping for a little less wind so I can try it out properly.
 
The chopped airbox gives a shedload more torque just where you want it. As to stumble below 3 k even when the emulsion tubes and needles are in fine fettle they are still lumpy buggers that don't like running much below 3k, I found the best bet for smoothing out the low end was 41mm FCRs (39's would probably do too) vast improvement over the BSTs worn or not.
I used to have a MkIV 900SL from new and that was still lumpy sub 3k but my current MkIII SL was really bad on worn BSTs, FCRs have really helped on that one. PS if your not riding in sub 10deg C much I wouldnt worry about plumbing the carb heater pipes in but if you are I can vouch 1st hand for what iced carbs on a 900SL feel like , ie bloody awful with misfires/coughing flatspots and stuck throttles, my MkIV SL used to suffer badly on the early morning commute and in cold fog.
 
+10C?...........positively tropical. As long as the roads aren't icy then it's fine by me. Know what you mean about cold fog. I've noticed that if my visor starts steaming up at 'normal speeds' then about 5 minutes later I get icing symptoms.
 
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Derek said:
Also, set the float heights to 14mm and the idle screws at 3.5 turns out for starters. You can fine tune them once you see how it behaves on the road.
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Er, 14mm from where to where? Had a look at mine today and they are 9mm from the flange to the highest tip of the float while the needle is just seating.
 
Have a look at the Factory Pro site. It is easier than trying to describe it. You don't need their fancy tool although it probably makes it easier but you will need to make a small plate to hold the pivot pin in place with one of the float bowl screws or you won't get a consistent measurement.
 
That was the way I checked the floats. Seems a big difference between 9mm and 14mm. Out of curiosity I checked the other carbs I have and they were 8mm. I've put the carbs back together unadjusted for the moment. The bike is less 'dramatic' to ride now as the throtle response is more linier. It doesn't feel like it charges to the red line with the alacrity it had before but that could easily be me getting used to it.

I got a pleaseant surprise today while cleaning out the clutch, it's an aluminium Corse job :D. Is there any 'aproved' way of cleaning the clutch out without creating your own mini dust storm? Wash it out with a garden hose for example?
 
Ok, did the 14mm float height adjustment under a bit of doubt. It works quite nicely. I can hear more mechanical noise which means there is less from the exhaust. The engine feels slightly smoother, power delivery a bit more even and low r.p.m. behaviour is a little nicer. The bike will cruise under 50kph and about 2700rpm without much complaint. Pity I didn't do this before the rally last weekend.

I'm going to check the ignition timing and pick-up clearance next. Carb balance is a tiny bit out but I'll fix that too. I've been studying the Ignitech literature and various forums and it looks like I know what I'm going to buy myself for my birthday.
 
Serious Black said:
I've been studying the Ignitech literature and various forums
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I think I'm going to go down this route too.. it is out of line with my plan to keep everything as old school as possible but with the need to retard ignition by an as yet unknown amount to prevent the HC pistons melting, it does seem by far the easiest way to go.

As I'm working on the bike at a glacial pace at the moment you will probably get there first so be sure and start a new thread, load plenty photo's etc. :)
 
Ignitech + 2 coils and cable ordered, 212 euros. Less than 2 Dyna coils hereabouts. Coming via DHL so I'll have to pay 17.5%vat plus what ever the robbing @@@@@@@s charge me for the service. Don't like DHL!

Derek, anychance of sticking this over into the projects section and re-naming it something appropriate? For tidyness's sake - Plus I can keep updating it with any other stuff along the way.
 
Thanks Derek.

Now this is officially a project I can keep some sort of order to what I've done. Might help somebody else down the line.

After a week living with the new float level I've learned a bit more. The bike doesn't start as well when cold, so much so that I'm going to have to re-adjust it back up a bit. The choke is less of an on/off affair which helps. The biggest problem is the warm up time is considerably longer.

With the standard 9mm float height the tang on the float is straight out and looks 'right' like this while the 14mm float height leaves it with quite a bend. This makes me think that the 9mm height is what Mikuni intended.

My suspicion is that the idle jet is a bit on the large side so what I'd like to do is set the floats back to standard and fit a 37.5 idle jet as per the American market and see what happens. The reasoning behind this is that the idle mixture screw is about 4 turns out with the standard float height. The idle mixture screw calibrates best about 2 to 2 1/2 turns and this is what most jap bikes are set around. When I set the idle mixture I screw the adjuster in until the engine note changes then back it out 1/4 turn.

I'd like to get the idle mixture right before I start fitting the Ignitech kit, that way I should end up with the optimum setting. At the end of all this I hope to have a bike that is nicer to ride until I get to decent riding country and have a good basis for further tweaking.

When I ordered the Ignitech I went for their coils too. This was for two reasons. The first, I've never heard of anybody using them and I'm just plain curious to compare them with the standard coils. The second reason is simple economics - they are considerably cheaper than Dyna coils.
 
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Ok, it's here already! Pity I haven't the time to fit it for the next two weeks the way things are going. I have read the manual - honest and had a practice assembly. The coils are probably the most interesting for most people. They came with plug caps fitted and the HT leads can be changed. I'll measyure the resistances of the coil and also the plug cap. The caps are in made from hard plastic like NGK and I'm hoping they are 5k ohm as I have a nice set of waterproof silicon caps. Probably my main problem is a software one as I don't have a PC with windows on. The USB to com cable is a nice quality chinese one. Installation wise I'll have to make up something to mount the brain and I hope to move both coils together over to the left of the bike. This will probably be the hardest bit. One other nice touch with the coils is they have + and - marked on them. The -ve terminal obviously goes to earth. This is important so as to get the spark polarity correct. The spark apparently needs about 60% more energy to jump from the earht electrode to the centre than the other way. Anyway heres some pics of the bits
 
Watching with interest,I have been looking at this ignition for an alternative setup for my TT2 project (Grandfather of 2v belt drive motors) hopefully this will work as well, this link may be of help to you if you have not already found it! Sam http://www.bikeboy.org/ducati2vignition.html
 
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Got a quick 5 mins in the garage when I parked the bike tonight. Coil primary resistance is 3 Ohms, plug caps are 5k Ohms. Couldn't get a secondary resistance but will try later. Look's like the coils might be comparable to Dynos.

It looks like I might get a couple of hours in the garage tonight so I'll be re-adjusting the carbs and fitting my Xenon light. The nights are fair drawing in here now and the mornings are black as the earl 'o' hell's waist coat. I'll also plan the fitment.

On the daydreaming side, I'd like to try a Throttle Position Sensor or Manifold Air Presure sensor. That could make for a very civilised bike and truly amazing fuel economy.
 
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