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Db4 Gearing

 
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DB1 860



Joined: 23 Mar 2014
Posts: 158
Location: Sydney

PostPosted: Tue Jan 12, 2021 5:03 am    Post subject: Db4 Gearing Reply with quote

So I rode my Bimota to the mechanic's the other day for its blue slip which is required to register a imported bike,

I felt the gearing was a bit tall, so I'm thinking of changing the gearing from 15/38 to 14/38.

So the question is what does everyone else run? has anyone tried 14/38 and where can I buy a front sprocket. Are they the same as a Ducati 900ss?
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2bims



Joined: 03 Apr 2010
Posts: 7074

PostPosted: Tue Jan 12, 2021 8:06 am    Post subject: Reply with quote

I'll check the gearing on my bike and get back to you....but the answer to your question is....No....the front sprocket is a Bimota one off.....Bimota build their bikes and then design a one off front sprocket to get the chain alignment correct.....the front on these is offset by quite some distance compared to a Ducati 900SS/ssie....the engine in the DB4 is actually from the Ducati Monster of the time....silver/grey engine casings...as Ducati had gone the fuel injected route on their 900ss in 1999/2000......the only carbed bike they made was the Monster at the time.....
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DB1 860



Joined: 23 Mar 2014
Posts: 158
Location: Sydney

PostPosted: Wed Jan 13, 2021 1:54 am    Post subject: Reply with quote

Mmm... so where are DB4 owners buying their sprockets from? There's a heap of sprockets on ebay reporting to fit a DB4, but they dont look the same as mine.

and what about that recessed plate that holds the sprocket on? that would wear over time.
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2bims



Joined: 03 Apr 2010
Posts: 7074

PostPosted: Wed Jan 13, 2021 10:16 am    Post subject: Reply with quote

DB4 Spare parts manual lists the sprockets as 15 and 38 tooth...Front/Rear...I have to say...I've never felt like it was undergeared...I think I've hand my DB4 around 10 years now......although it doesnt get used as much as it deserves to....as it is practical, comfy and rides well.....

I think I may still have a spare front sprocket so I'll go see....and yes...the locking ring with the teeth can wear out....and then the sprocket can float around......theres a few specialist companies that sell for DB4 the offset sprockets....and I'm sure Paolo of BCP will have some also...Oh no...I've just checked the spare parts codes for the sprocket and retainer....it shows nothing...
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2bims



Joined: 03 Apr 2010
Posts: 7074

PostPosted: Wed Jan 13, 2021 10:22 am    Post subject: Reply with quote

I'm curious that you felt the gearing to be "too high"...what led you to this conclusion?....does the bike idle at standstill.....is it hesitant to pull away and you have to rev past 4thou to get off the line? Low idle jets blocked?..Or...is your clutch on the way out and thats what makes the gearing seem tall?...when its just starting to go this is what it may feel like...but check revs against speed increase...needles should both be rising at the same rate...if revs rising at higher rate than speed...then its clutch plates....try pulling them out and looking/cleaning....also check the clutch line isnt full of old fluid/air.....a wrongly set up clutch is not so great for progress....

What model is it? Carbie? Is the undertank Paioli vaccum fuel pump still good>? It works off suction from connection with a rubber tube to one of the intakes on the rear cylinder...works like a fish aeration filter pump....merely air and rubber diaphragms.....causing suction.....with age the rubber perishes and slows fuel flow....
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brian



Joined: 22 Aug 2011
Posts: 3648
Location: Australia

PostPosted: Wed Jan 13, 2021 2:38 pm    Post subject: Reply with quote

I’ve never thought that my DB4 was too high geared either. In fact at highway speeds I don’t think I’d want it geared any lower
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Current motorcycles - '99 Bimota DB4 #104, '96 Bimota SB6 #1165, ‘94 Bimota DB2 J #652, '99 Bimota DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, ‘94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, ‘61 BSA A10 650
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DB1 860



Joined: 23 Mar 2014
Posts: 158
Location: Sydney

PostPosted: Thu Jan 14, 2021 4:24 am    Post subject: Reply with quote

This high geared assumption was bought about by a trip to the mechanics, I don't think I took it out of second gear, will do a proper road test once its registered.

I have put in a new clutch slave and master, repacked the clutch , and a new vac fuel pump,

It idles alright but I may get the flatslides serviced as the bike could have been sitting around a bit
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vort28



Joined: 22 Mar 2010
Posts: 2178
Location: Northwest , UK

PostPosted: Thu Jan 14, 2021 9:39 am    Post subject: Reply with quote

I bought a standard front sprocket and then had the recess machined into it. (DB2 is the same ).
I do however run a 41 rear as prefer the lower gearing for the twisty's . Avoid straight roads at all costs !! Therefore not bothered about 90mph+ .
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2bims



Joined: 03 Apr 2010
Posts: 7074

PostPosted: Thu Jan 14, 2021 10:19 am    Post subject: Reply with quote

DB1 860 wrote:
This high geared assumption was bought about by a trip to the mechanics, I don't think I took it out of second gear, will do a proper road test once its registered.

I have put in a new clutch slave and master, repacked the clutch , and a new vac fuel pump,

It idles alright but I may get the flatslides serviced as the bike could have been sitting around a bit


Ah...you mention Flatslides......whats on it? evidently not the stock 38mm Mikunis.......Which is what myself and Brian are running.....what airbox set up do you have or no airbox and K&N one filters?...Are they clean?

Vort is also running Flatslides as his is a DB4 Corse.....with Open Corse end can and Keihin 39mm flatslides......running with those it may seem a bit flat down low....as the flatslides arent really getting the use they are intended for....My DB2 is a 944cc big bore kit...High comp V2 billet pistons and V2 cams.....and a pair of Keihin FCR41mm flatslides sucking on K&N Cone filters.....and open ended twin can Moto Corse end cans....But on that I run a smaller rear sprocket not larger.....Clutch is updated to a corse billet clutch basket and Barnett Billet HD Clutch plate pack...etc etc....I do have to slip the clutch in first...but I like doing that and then it just pulls and pulls all the way through the gears....Flatslides also have to warm up before they fully come alive...Do you have a knurled knob cable fed adjuster on the carbs to allow adjustment up and down whilst riding?
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DB1 860



Joined: 23 Mar 2014
Posts: 158
Location: Sydney

PostPosted: Fri Jan 15, 2021 3:47 am    Post subject: Reply with quote

Its running 39mm flatslides, I was wondering whether they where the reason for the motor requiring revs to get off the line. The filters are clean but quite small, I was thinking of putting in larger foam filters.

I can see the idol adjuster through the frame, certainly couldn't get to it while riding.

So Vort whose rear sprocket did you use? i noticed that mine has a bimota stamp on it. 15/41 is close to 14/38, I'm test riding this bike in the weekend, then I will decide if I need to change the gearing, I've found someone who can modify a sprocket for me. One thing I don't like about low gearing is that you are for ever having to change gears and not getting the benefit of the torquey motor.
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agusta74



Joined: 25 Oct 2011
Posts: 39
Location: New Zealand

PostPosted: Fri Jan 15, 2021 5:55 am    Post subject: Reply with quote

This has some good info on gearing and charts!
http://www.bikeboy.org/ducgearing.html
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2bims



Joined: 03 Apr 2010
Posts: 7074

PostPosted: Fri Jan 15, 2021 8:40 am    Post subject: Reply with quote

DB1 860 wrote:
Its running 39mm flatslides, I was wondering whether they where the reason for the motor requiring revs to get off the line. The filters are clean but quite small, I was thinking of putting in larger foam filters.

I can see the idol adjuster through the frame, certainly couldn't get to it while riding.

So Vort whose rear sprocket did you use? i noticed that mine has a bimota stamp on it. 15/41 is close to 14/38, I'm test riding this bike in the weekend, then I will decide if I need to change the gearing, I've found someone who can modify a sprocket for me. One thing I don't like about low gearing is that you are for ever having to change gears and not getting the benefit of the torquey motor.


A little bit of that "befuddles" me somewhat......I've always found that you are forever changing gears on a Ducati V-twin....its what I like about them....you are out and about on a lazy V-twin that requires your attention to get the most out of it.....if you are out and about in the mountains on a twisty trail, going up and down hill....its like a 2-stroke...it demands your attention....try riding a Vdue.....First time I took mine to the TT I got it all wrong...I was 3 gears out on one famous ben.....dropped it down a cog....whirr....splurg...another gear...whirr...splurg....another gear.....uuuuhhh....eventually..it started to climb...very embarassing...but I got used to it after that...its the same with my 7 gear Cagiva SuperCity 125......precise gearing at the right time before exiting corners is essential to get the most of it...and clutch slipping off the line is essential at 5-6thou.....the Vdue used to eb the same until I rejetted it....

What make of flatslides? Mikuni or Keihin?....When cold and when warm...whats the tickover?....1500 and 2500 for me with Keihin FCR41's...I run K&N Mesh filters....large large large.....bigger surface area than foam....due to wavy construction.....I think Vort has a Talon rear sprocket....as he has carbon dymags on his DB4...and thats what they supply to whatever gearing you ask....Not sure on mine...its a talon also....As I also have dymags on my DB4.....cant reach the bike at the back corner of the garage at the moment...

Knurled adjuster I have a long one that feeds up the side of the LHS frame out and out at the front of the tank...and can be tweaked down at traffic lights when the flatslides are warmed up

All Bikes are toys...and toys are to be played with....an Ex girlfriend of mine used to ride my ZRX1100...she loved it...but mainy because she could lock it in 3rd gear and ride all day long without changing...even when overtaking....in-line 4's more low down grunt and pull when you ARENT in the best gear....When I had a Ducati 750SSie....that had more low down grunt and torque pull than either my DB2 or DB4....but evidently would lose out somewhat at the higher end....less high..more low...900....less low...more high...but thats "race" technology
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brian



Joined: 22 Aug 2011
Posts: 3648
Location: Australia

PostPosted: Sat Jan 16, 2021 7:46 am    Post subject: Reply with quote

2bims wrote:


What make of flatslides? Mikuni or Keihin?...



If they’re 39’s they would be Keihin FCR’s


.
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Current motorcycles - '99 Bimota DB4 #104, '96 Bimota SB6 #1165, ‘94 Bimota DB2 J #652, '99 Bimota DB4 #088, '08 VTX1800, '93 ZXR750R M1, '95 ZXR750, '95 ZXR750 Race Bike, ‘94 CBR400rr NC29 Race Bike, '94 CB250, '49 BSA C10 250, ‘61 BSA A10 650
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vort28



Joined: 22 Mar 2010
Posts: 2178
Location: Northwest , UK

PostPosted: Mon Jan 18, 2021 8:44 pm    Post subject: Reply with quote

DB1 860 wrote:
Its running 39mm flatslides, I was wondering whether they where the reason for the motor requiring revs to get off the line. The filters are clean but quite small, I was thinking of putting in larger foam filters.

I can see the idol adjuster through the frame, certainly couldn't get to it while riding.

So Vort whose rear sprocket did you use? .


Can't say my DB4 needs revs to get it off the line TBH. OK its a Duc so it requires a certain amount of rev's so as not to do a kangaroo impression, but thats just a vee twin thing . I have K&N cone filter's on my 39's , would say they are a reasonable size , probably 100mm tapering to about 50 , and about 150mm long ( from memory ) . I'm assuming if you have the 39mm flatsides you have the modified tank ?
Obviously one thing I do have is the open can. When I have put the standard can on for an MOT it ran like a pig !!!! Have the carbs been set up correctly ? Have you got a different can ?
As 2Bims says I have Dymags on my DB4 so I got a different size sprocket supplied with the wheels ( its not Bimota bolt pattern ) , I'm also pretty sure I got 2Bims the same size sprocket when I got his wheels for him.
I don't really find the gearing requires excessive gear changing TBH , can't really remember why I changed the ratio , but guess must have found it over geared or i would have got the standard size when I bought the wheels.
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