Ducati 900ss Running rough

[sopachrga]

Hi guys

I've picked up an older 1993 Ducati 900ss.
It hasn't been ridden much for the last year or two, and as expected it's running like s**t.

On cold start, it won't idle at all. It has to be ridden for 10 mins or so before it'll idle.
For that first 10 minutes, the bike is VERY low on power and sounds rough. At some point it 'magically' and instantaniously smooths out and gets full power (This comes as a shock when it happens!).
It will also idle from that point.

In saying that, even once it's running at full power, it's a bit rough and surges at low speed. Also back fires pretty impressively on deceleration.

I've checked the plugs, they are new, and gapped properly. They look nice and clean.


Where should I start looking to fix this?
Should I just take it to a shop and get them to do a full carb setup?

[SVboy]

I can't really help with your issue but I suggest Duane of Duanes bikes n skis as a very competent Ducati mechanic. Located in hornby.

[sopachrga]

Cool, thanks for the recommendation.
Will give him a call if all else fails.

[Voltaire]

My mate bought a 600 and it was doing that, turned out to be an ignition module. They have one per cylinder.
Fastbikegear do an ignitech drop in unit, don't waste time or money on Ducati ignition units.
The carbs take a while to warm up too.

[sopachrga]

I'll check them out.
Thanks

[Big Dog]

Before you pay someone it may be a good idea to drain your fuel and top up with fresh stuff.
This is sounds an awful lot like the carbed bikes that live here when left for longer than 2 months.

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[AllanB]

Agree re fuel. It is good for about 6 months before it starts to deteriorate. Had a similar issue years ago with a bike I had had sitting for some months - went through everything with no improvement and as a last resort drained the fuel and float bowls and put fresh stuff in. Fixed.

[sopachrga]

I've put about 450kms on it since I got it. So it's had a couple of tanks of petrol go through it now.

Would it still be worth doing? I would have thought the old fuel would have passed though or be diluted enough by now?

[Big Dog]

Does your choke move freely?

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[sopachrga]

It does seem to move ok. But it doesn't seem to do much when it's on. I can see it moving the sliders on the back of the carb as I operate it though.

I would have expected it to increase the revs when it's on, but it doesn't seem too. It will make it stall if I turn it on while the bike is hot and idling though. So I guess that means it's working ok?

[Big Dog]

It does seem to move ok. But it doesn't seem to do much when it's on. I can see it moving the sliders on the back of the carb as I operate it though.

I would have expected it to increase the revs when it's on, but it doesn't seem too. It will make it stall if I turn it on while the bike is hot and idling though. So I guess that means it's working ok?
I don't know the techy reason but your choke doesn't seem to be doing much choking cold.
Carb cleaner maybe?

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[Big Dog]

Perhaps reach out to some of the guys that talk about carbs a lot.
NZSPOKES comes to mind.

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[sopachrga]

Sounds like that and some new coils could be worth a shot.

[Big Dog]

If this were the tab I'd be putting a fiver on the carbs for the win.

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[sopachrga]

Ok. I'll start there and see how I go.thanks for your help.

[BMWST?]

my brand new ducati 900 s2 ran like that once as i was approaching Te Kuiti,Upon inspecting said beast it was apparent that both carbs were about to fall off.The rest of that trip was made with one nut and stud holding on each carbie....so check for air leaks

[AllanB]

Nah - if you have gone through a couple tanks it is well diluted. I'd drain the float bowls - see if any grud comes out (it should not).

[nzspokes]

I would be asking the Duc mechanic listed above in case its something generally known. But does sound a lot like a blocked idle circuit in the carbs. As the idle jets tend to be .3ish mm it does not take much to clog em. This is a guess as I have not worked on one of these hence best to talk to an expert on them.

Also check for loose clamps on the carbs, air leaks from perished hoses.

[sopachrga]

Cool.
Checking the hoses etc sounds like a good idea. I should have thought of that. It's probably of the age now where they could start deteriorating.

[Voltaire]

Run each cylinder separately, take the lead off and with a spare plug ground the plug. Watch the spark. The other cylinder should fire up ok. Don't run an ignition with no plug on the end though.
If you run the bike up and down the road for 5 minutes touch both cylinders, one will probably be obviously cooler than the other.
I find on my old bevel that if one plug fouls, it will run on one, then the other will kick in and it takes off.
After yesterday with my BMW track bike, I'm a Dyno convert.

[sopachrga]

So, progress update.

After running through all diagnostics, I've found there is no spark on the front cylinder when cold. Swapped Cdi and coils over and problem still existed on the front.

Tested pickup coil resistance, one reads the correct 97ohms. The other over 290Kohms.

So, looking pretty damning that the pickup coil is dead.
Not sure if I'm keen to do the work myself.
Anyone with experience in Chch be willing to assist for some beers? Haha.

Otherwise will call the previously suggested mechanic and get a quote.

[OddDuck]

Hey mate - have a 900ss, 1995, and been through exactly what you've described.

California Cycleworks - check their site and look for their ignition coils. I bought and installed these and they helped the bike enormously. Also much cheaper than OEM.

It looks like they don't do the Keihin FCR41 kit anymore which is a bit of a shame. I put these on (it's a bit involved if you keep the airbox) and general bike good behaviour followed. They are much much better than the stock Mikuni's.

You mention carb choke slider, so I presume you're still running Mikuni's. My experience with mine was that they had a serious problem with the plastic diaphragm covers. Big (on top) and small (on side), they are both secured with two screws across their diameter, and they bow over time. Traces of dirt inside the carbs showed very clear vacuum leaks. The main needle also has a nasty habit of wearing an oval into its flow tube. My bike ran horribly rich, all sorts of problems. Tried everything before I finally replaced and upgraded. See how you go of course - your plugs sound fine, but if they start fouling up then I'd take a very careful look at the Mikuni's.

Other things... check your tank breather valve (the little aluminium goodie on the rubber hose, outside the tank, bridging to the hose running through the steering stem). It's barbed to the hoses (pulls off) and pressed together, lightly (pulls apart, with vise and vice grips). Try blowing through it before applying the machinery, of course. It should flow freely one way, and pass a little slowly the other. There's a disc of rubber in there which is horribly prone to expansion if it meets ethanol. Modern gas has ethanol introduced, so, well... Mine jammed. Wasn't a big issue when running but a heat-pressurised tank had a nasty habit of forcing petrol through the carb's needle valves and flooding the motor.

Also check your earth connections. I'd found the factory earths had aged badly. The bike started and ran a lot better with newly crimped spade lugs on welding lead cabling.

Hope this is useful.

[sopachrga]

Awesome. Thanks so much for the info.
I'll get the pickup coil sorted first, then start looking at the rest of your suggestions.

[OddDuck]

So, progress update.

After running through all diagnostics, I've found there is no spark on the front cylinder when cold. Swapped Cdi and coils over and problem still existed on the front.

Tested pickup coil resistance, one reads the correct 97ohms. The other over 290Kohms.

So, looking pretty damning that the pickup coil is dead.
Not sure if I'm keen to do the work myself.
Anyone with experience in Chch be willing to assist for some beers? Haha.

Otherwise will call the previously suggested mechanic and get a quote.

Oh whoops, have just re-read your post. I've been in to the alternator cover, too. Here's how to have at the pickup coil:

Left fairing off, chain sprocket cover off, try to get the kickstand bracket off (it just - only just - manages to get in the way).

Unfortunately Ducati really fucked up with the kickstand bracket bolts. They're loctited in, they're 10mm threads, and they used a dinky 6mm socket hex on the head. The head is large diameter and likes to heat-weld itself into place on the bracket. High torque needed, incredibly easy to burr. Drill them if you have to (the heads will pop off), you can use vice grips on the stubs to remove them from the engine case since they'll stand proud by about 12mm.

Remove ALL cap screws around the cover perimeter. A couple of them are in by the chain sprocket. Double check, get in there with kero and a brush if unsure. They like to hide behind grease and dirt.

Then you can use a small beam-and-pillar bearing puller to pull the cover off, if you have a couple of long enough M6 bolts and mudguard washers. Otherwise there are dedicated tools you can order online (try Ducatispares, down in Winton, Southland - he's good).

After all that, replacing the pickup coil is a piece of cake. You need to use a feeler gauge to check spacing between pickup point and the flywheel, but that's the only tricky bit.

Clean everything, silicone the case perimeter or use a gasket (again, Ducatispares, if you have to go that route), bolt it all back together.

While you're in there, have a long hard look at the alternator's stator winding. If there are any brown or black windings visible (after cleaning engine oil etc off), replace it. If the stator's on its way out, it tends to take the regulator down with it since it'll throw some voltage spikes down the line. I ended up about $500 out of pocket with this, two regs failed before I realised what was going on.

I used new OEM bolts on the kickstand bracket but I'd go with some of the Champion 12-grade hex head bolts if I had to do it again.

[sopachrga]

Perfect. Thanks for that. Really useful!

[sopachrga]

Last update.

Thanks to everyone who contributed advice, it was all really helpful.
I replaced the pickup coil last night, and it has fixed the issue. I think the carbs could still do with a tune/balance, but that's pretty minor now.

Starts,idles and runs so much better.


Oh, I also want to mention how great the guys from Ducati Spares (http://www.ducatispares.co.nz/) were. They sent out the parts I ordered overnight, and had really good prices!

:banana:

[F5 Dave]

Cool to have sorted issue. Get onto the factorypro site and dig around to read about emulsion tubes. Once they wear carburation becomes problematic. Known issue on these carbs but they sell spares. Pull the tubes out and eyeball for ovality in real good light. Tiny wear will make for issues that can't be tuned out and will darken plugs so check plugs.

[sopachrga]

Sweet. Will check them out.

[nzspokes]

Woot, glad its sorted.

I use a magnifying glass to check the needle jets.