Smoother low revs. - Page 2 - Ducati.ms - The Ultimate Ducati Forum
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post #11 of 82 (permalink) Old Apr 24th, 2019, 2:30 pm
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Vacuum sync the carbs as well
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post #12 of 82 (permalink) Old Apr 24th, 2019, 11:28 pm
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Originally Posted by BelgianDuc900SS View Post
Flywheel is stock. And gearing will indeed be the first thing to try.
I'll try a 15/39 to start with an go from there.
15/39 is what I run - you'll find that it takes your minimum 'trickle around' speed from around 50 kph (at ~ 3000 rpm), down to 30 kph at the same revs. I also found no difference to my top speed - the engine just revved a little harder. I did like how the change closed up the gaps between gears - both for upshifts and downshifts.


<cough> - I know you don't want to hear this - but FCR's also help low speed running... Hmm - now I mention it - nothing has made much difference to my top speed - but it HAS made a difference as to how fast it gets there.

And yes - cobblestones are bastard things to ride on. Been there.
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Mods are: K&N filter, airbox lid on with rubber trumpets removed, MBP collets, full SMI (SilMoto Italia) spaghetti exhaust with 'open' carbon cans, 41mm FCR's - #182 mains!, Barnett alloy clutch basket, Oberon slave cylinder, Ohlins fork springs, Ohlins rear shock, Verlicchi swingarm.
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post #13 of 82 (permalink) Old Apr 25th, 2019, 8:54 am Thread Starter
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Originally Posted by ducvet View Post
You may even consider +3 in the rear if there is room in the chain adjustment. If not the best way would be to buy a 14 tooth front.

If you are putting all new chain and sprockets go +3 in the rear and cut the chain so the adjustment is forward of the middle of the range. This would allow you to go -2 later if you decide it is too much (I doubt it would be) and still have adjustment range. If you are NOT changing chain now you should be able to go +2 in the rear and fit or -1 in the front. front sprockets can be had for cheap $$ so many go this route, good for testing. The -1 front is about =2.5 rear so it gets you a close idea.
That's a good idea. I think I'll try that.
Front sprocket is cheaper and easier to change.
I'll only change the front sprocket as the chain and sprockets are basically new (<2000km).

The chain adjusters are right in the middle now (15/37) so it shouldn't be a problem switching the front sprocket to 14 teeth without cutting the chain I suppose.

Thanks again, ducvet!

1997 Ducati 900 SS Full Fairing
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post #14 of 82 (permalink) Old Apr 25th, 2019, 9:00 am Thread Starter
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I almost never go on interstates with my SS, so I have found 15/41 perfect for back roads, including all the small town stop and go.
As far as making the bike run smoothly below 3000 , it can be done. Youíve already replaced the jet needles and emulsion tubes, they are the big wear items in the carb. Synchronize your carbs as best you can. Make sure your pilot jet is big enough. You might be able to use what you have, adjust the mixture screws ccw about 3 1/2 - 4 turns to start, adjust when weíll warmed. With warm engine, air filter out, watch the diaphragm slides rise. They must rise together at lower rpmís if the bike is going to run smoothly. If they donít, check the diaphragms for leaks or damage, replace the o rings in the caps, and make sure the slides move freely. New plug wires and caps and plugs help the bike run smoothly. Itís old.
Carbs are recently rebuild and adjusted, diaphragms are checked and plug wires, caps and plugs were renewed six months ago. Oil and filter are changed, K&N airfilter was cleaned, exhaust gaskets are new...
All this definitely made the bike run much smoother.
I expect to be quite happy with it once I've changed the front sprocket to a 14 teeth.

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post #15 of 82 (permalink) Old Apr 25th, 2019, 9:13 am
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<cough> - I know you don't want to hear this - but FCR's also help low speed running...

Just to be clear this is NOT a paid advertisement for FCR's , though they should pay us

If we keep this up maybe the mods will let us start a Keihin FCR board on here...lol
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post #16 of 82 (permalink) Old Apr 25th, 2019, 9:15 am Thread Starter
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Originally Posted by steveb64 View Post
15/39 is what I run - you'll find that it takes your minimum 'trickle around' speed from around 50 kph (at ~ 3000 rpm), down to 30 kph at the same revs. I also found no difference to my top speed - the engine just revved a little harder. I did like how the change closed up the gaps between gears - both for upshifts and downshifts.
Sounds good, I hope to achieve similar results by changing the front sprocket.
And top-speed? I really don't care. Never even tried it. Never do track days. So whatever happens to top speed, I really don't care.


Quote:
<cough> - I know you don't want to hear this - but FCR's also help low speed running... Hmm - now I mention it - nothing has made much difference to my top speed - but it HAS made a difference as to how fast it gets there.

I know about the FCR's. I don't have a problem with them either. Great looking carbs and (as far as I know) great performance. They are just a bit expensive to me (€1000 carbs on a €2000 bike...).
Once I know that I'm gonna keep this bike 'forever' then I'll reconsider the FCR's again. But for now they are just too expensive.
And then there's the choke issue. Belgian weather can be rather cold and wet...
Maybe later. I'll let you know!

Besides that; I think I once read an article about FCR and it was said there that if you go FCR for more power at low revs you should go for the 39mm version. The 41mm are better for power at high revs.
Any insights on that anyone?

Quote:
And yes - cobblestones are bastard things to ride on. Been there.
Double feeling about these things.
They look great in an old town centre. Nice for postcards and exciting at a bicycle race (Paris-Roubaix anyone?).
But hell to ride on, especially when wet.

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post #17 of 82 (permalink) Old Apr 25th, 2019, 9:25 am
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Worn or dirty sprocket and chain can cause this issue. My bike with a new chain and sprocket kit (900ie) will run smooth down to 2,5k RPM at low speeds. It will run smooth even at sub 2k RPM, but that's not good for the engine

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post #18 of 82 (permalink) Old Apr 25th, 2019, 9:26 am Thread Starter
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Originally Posted by ducvet View Post
Just to be clear this is NOT a paid advertisement for FCR's , though they should pay us

If we keep this up maybe the mods will let us start a Keihin FCR board on here...lol
To be honest: when I bought this bike, I've always tought; "These things are way too expensive, I'll keep the Mikuni's. If they're good enough for Ducati engineers, they're good enough for me. Not interested."

But the more time I spend on this forum the more I'm driven towards FCR's. I've already checked availability, pricing, mounting instructions, reviews...
It will not be a project for this year but I'm almost sure that if I still ride this bike in a year or two, Keihin will be mounted.


You guys shoud indeed be paid by Keihin!

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post #19 of 82 (permalink) Old Apr 25th, 2019, 10:16 am
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A 14 tooth sprocket is a really quick and easy fix on these bikes.
I found smoothness was really helped by fitting up-rated coils as they give more even firing. You can get a CaliforniaCycleWorks kit from ExactStart in the UK.
If you join the Ducatiukforum and subscribe, ExactStart will give you a good discount

Ps I would also highly recommend ordering a starting circuit cable kit from him. It will transform the way your SS cranks and starts Again, the discount applies.

http://www.exact-start.com/available-kits/

http://www.ducatitech.com/2v/aftermarket/dyna_kit.html

Last edited by Old rider; Apr 25th, 2019 at 10:31 am.
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post #20 of 82 (permalink) Old Apr 25th, 2019, 10:42 am
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I would not claim 39's are smoother than 41's at low rpm's just that they feel more responsive and I have yet to see a big enough benefit on any of the bikes here to go with 41's. I do own both so one of these days I will do a back to back test on the same bike to answer this question for myself.
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