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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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 Posted: Tue Jun 17, 2014 7:40 pm Post subject: |
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| brian wrote: |
Here's a weird thing... 3 weeks ago before I pulled the carbs out, I removed the front plug as it wasn't firing. When I got the plug out the porcelain top of the plug was broken. I thought I must have broken it with the plug socket as it was a bit awkward to get at it with the fairing on. Yesterday when the bike wouldn't start after fitting the carbs, I removed the plug lead from the rear plug and the top of the plug came off in the plug cap. The porcelain part broken. I couldn't have broken this one as I hadn't even put a plug socket on it as yet. I've never seen a broken plug in my life, now both plugs in this thing were broken??? May have been a dud set of plugs.
I'm nearly ready to throw the towel in |
Well, a Bimota never was intended to be "wrench-friendly", some models (YB) even needed to lower the engine block just to replace the spark plugs. Ever worked on a Mantra, like taking the fuel tank off?
On the db4 the spark plug of the vertical cylinder is obscured by a nicely brushed aluminium frame beam. I made myself a fitting spark plug socket for that and forget the torque wrench there. Still some fiddling to replace the spark plug. The horizontal cylinder spark plug can be reached easily but only with the lower fairing taken off. Otherwise you're wrenching in an awkward position risking in damaging the spark plug. So just take the lower half off (you can leave both lower sides together and ease it away underneath the engine, protecting the paint work with a blanket spread out under the engine).
On my db4 there are now just 2 parts that form the complete fairing: the lower half (LH and RH glued together as one piece, works great) and the top half including screen panel, side panels and under headlamp panel. These all stay together and you can ease it off the bike towards the front slightly opening it up around the inner fork tubes. So it's 5 screws for the top part and 2 screws for the bottom part. Dzus fasteners connect the upper and lower parts. It saves a lot of work compared to fully dismantle the fairing.
Broken insulators mostly are caused by low end (low quality) spark plug sockets that don't support the spark plug well and can put force on the porcelain insulators. But maybe that erratic running is caused by these cracked spark plugs? Just put in new ones with good tools and try again.
Don't give up on the db4, it appreciates a caring owner and rewards it with superb behaviour. 
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Track riding on a Bimota: FUN! |
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Tue Jun 17, 2014 7:46 pm Post subject: |
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| 2bims wrote: |
Try not to despair Brian....if you wanted an easy life then all your Bikes would be Hondas..and then you'd have no cause to spend all those happy hours in the stable of bikes.......and we all know that time in your man cave is allowed....but riding time is limited.
I'm surprised that for the sake of 85GBP you havent just picked up a whole new set of Mikuni 38's from that nice man I use in Italy....its what I bought for the pup I restored........plugged the twin cable throttle in...linked up to hoses...and first crank of the bike when fully constructed and the darn thing scared the life out of me by firing up first time.never touched any of the internals or anything...Can dig out the link to his site and the carbs again if you like...........?? |
For 85 GBP I would without any doubt get a fresh set of Mikuni's. And beef them up with a Dynojet Stage 2 kit, that would do the trick. Tou also might look for a Dynojet kit for the Yamaha TDM850, maybe these are cheaper than the "Ducati" kits, even if the might have identical parts. Just compare the part descriptions.
My best advice would be getting a set of Mikuni TDMR40, direct swap, no need for an other twist grip or special fuel tank. And all your carb problems will be vanished....
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2bims
Joined: 03 Apr 2010
Posts: 7289
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| Posted: Tue Jun 17, 2014 8:13 pm Post subject: |
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Are the TDMR40's a single throttle cable then? unlike Keihin Fcr's? and they would fit under the standard Bimota fuel tank? Do you keep the standard airbox with these or K&N cone filters etc?
Would like to change my DB4...tis the only bike I have that is absolute standard on engine, pipe, carbs etc...so does feel a little flat in comparison and as such always gets left at the back of the garage....
I'd put Keihin FCR39's on...but dont really want to go the route of heating the tank to get it to form to accommodate the carbs/Twin pull throttle...... |
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Tue Jun 17, 2014 8:47 pm Post subject: |
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| 2bims wrote: |
Are the TDMR40's a single throttle cable then? unlike Keihin Fcr's? and they would fit under the standard Bimota fuel tank? Do you keep the standard airbox with these or K&N cone filters etc?
Would like to change my DB4...tis the only bike I have that is absolute standard on engine, pipe, carbs etc...so does feel a little flat in comparison and as such always gets left at the back of the garage....
I'd put Keihin FCR39's on...but dont really want to go the route of heating the tank to get it to form to accommodate the carbs/Twin pull throttle...... |
TMDR40 set (bank of 2) are double cables (open/close) just like the stock. You don't need to change the cables nor the fuel tank. You can run them with the stock air box or pod filters. Remember: these are flat side carbs as well. And you'll notice the same difference in throttle pickup as the FCR's.
FCR's bank of 2 are the same setup, one cable for pull and one for close. Double pull only goes for separate FCR's.
Heating up the fuel tank to make room for the FCR cable routing is a pain in the ###. I did it myself and it was just enough after I had ground down the FCR cable bracket. The plastic material of the fuel tank is not really " thermo-shapable", you risk making the material brittle when you overheat. Now I use the special tank for the FCR kit and sold the original one.
I've got the FCR 41 mm just because my engine is fairly heavily tuned and because I could get them for a good price. I even did cut a piece out of the monocoque just LH front side for the cables.
For road use I would've chosen the TDMR40 without any doubt.
Well, I'll make some pictures of my db4 tracky tomorrow.
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2bims
Joined: 03 Apr 2010
Posts: 7289
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| Posted: Tue Jun 17, 2014 9:12 pm Post subject: |
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Cheers Deebee4...so to be clear....no nned to modify tank or bodywork for TDM flatlslides?
I only want to go to 40's as the engine is still stock...and I dont want the expense of 944 kit stage 2 cams etc etc...already have the Db2 modded bike for that...and even though thats track focused I only use it on the road...just looking for a better tune for the Db4 and maybe I'll use it a little more......What throttle grip did you use then? as the standard DB4 set up for the throttle twist grip is encompassed within the switchgear body for the starter/kill switch?
Last edited by 2bims on Tue Jun 17, 2014 11:34 pm; edited 1 time in total |
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Tue Jun 17, 2014 10:21 pm Post subject: |
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| 2bims wrote: |
Cheers Deebee4...so to be clear....no nned to modify tank or bodywork for TDM flatlslides?
I only want to go to 40's as the engine is still stock...and I dont want the expense of 944 kit stage 2 cams etc etc...already have the Db2 modded bike for that...and even though thats tack focused I only use it on the road...just looking for a better tune for the Db4 and maybe I'll use it a little more......What throttle grip did you use then? as the standard DB4 set up for the throttle twist grip is encompassed within the switchgear body for the starter/kill switch? |
When you swap the stock Mikuni BDST38 for a bank of Mikuni TDMR40 (like here: http://www.mikuni-topham.de/englishsite/TDMR_English/TDMR40B14SS_English.html)
indeed no need for changing fuel tank, just keep the original twist grip/switch gear and throttle cables. It all works. No need for changing filters/airbox (but recommended anyway).
I never had this TDMR setup myself, but a German friend with a roadgoing db4 had and he was very pleased with the simplicity of the carb swap and the improvement.
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Wed Jun 18, 2014 10:06 pm Post subject: |
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Here's some pics
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2bims
Joined: 03 Apr 2010
Posts: 7289
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| Posted: Thu Jun 19, 2014 11:14 am Post subject: |
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That sure does look clean and tidy and track focused...I even like the colour scheme....brings it fresh into the 21st Century and looks up to date and not 14 years old......well done  |
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Thu Jun 19, 2014 7:54 pm Post subject: |
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| 2bims wrote: |
| That sure does look clean and tidy and track focused...I even like the colour scheme....brings it fresh into the 21st Century and looks up to date and not 14 years old......well done |
Thanks for this nice compliment
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brian
Joined: 22 Aug 2011
Posts: 3769
Location: Australia
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| Posted: Mon Jun 23, 2014 1:48 am Post subject: |
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| 2bims wrote: |
| I'm surprised that for the sake of 85GBP you havent just picked up a whole new set of Mikuni 38's from that nice man I use in Italy |
Yes mate i very nearly did, and probably should have. Problem is, i just can't see anything wrong with my carbs. Some of the o rings were a bid dodgy so i bought 2 x new seal kits for the best part of a hundred bucks but it's still no good. I'll pull them out again when i get time and have yet another look.
Then i'll either go with the new CV38's or a set of 40mm flatslides if i can find a set that doesn't break the bank.
My problem is, i can't see the sense in replacing something that i can't fault. 
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'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 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, '89 ZXR750, '91 Ducati 851 |
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Mon Jun 23, 2014 6:05 am Post subject: |
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| brian wrote: |
| 2bims wrote: |
| I'm surprised that for the sake of 85GBP you havent just picked up a whole new set of Mikuni 38's from that nice man I use in Italy |
Yes mate i very nearly did, and probably should have. Problem is, i just can't see anything wrong with my carbs. Some of the o rings were a bid dodgy so i bought 2 x new seal kits for the best part of a hundred bucks but it's still no good. I'll pull them out again when i get time and have yet another look.
Then i'll either go with the new CV38's or a set of 40mm flatslides if i can find a set that doesn't break the bank.
My problem is, i can't see the sense in replacing something that i can't fault. |
Could you describe what carb problems you encounter? Like "it doesn't pick up well, but when I put the choke on it does better (or worse)" Or: " erratic idle, when I very gradually open the throttle it suddenly gets better at 4.000 rpm".
Try to discover when and where on the rev counter scale it does what, when it gets erratic use the choke to see if it improves or gets worse. Does it get better when you open the throttle fast or when you open it very slowly. Write it down and try to find connections. Or share t with us.
You'll discover if it's really the carbs acting up or still an electric fault. Have you checked the ignition pickps' and coils resistance according to the manual? A faulty pickup (or one with a wrong air gap) will cause erratic running too. Also an stroboscope neon light checking the ignition with the markings on the flywheel will show up erratic ignition too. It did on my db4 when I was fault finding.
Anyway: replacing the 38mm BDST Mukini's (even if these are perfectly in order) by a bank of 40mm TDMR Mikuni's will definitely improve engine behaviour.
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brian
Joined: 22 Aug 2011
Posts: 3769
Location: Australia
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| Posted: Mon Jun 23, 2014 4:24 pm Post subject: |
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| deebee4 wrote: |
| brian wrote: |
| 2bims wrote: |
| I'm surprised that for the sake of 85GBP you havent just picked up a whole new set of Mikuni 38's from that nice man I use in Italy |
Yes mate i very nearly did, and probably should have. Problem is, i just can't see anything wrong with my carbs. Some of the o rings were a bid dodgy so i bought 2 x new seal kits for the best part of a hundred bucks but it's still no good. I'll pull them out again when i get time and have yet another look.
Then i'll either go with the new CV38's or a set of 40mm flatslides if i can find a set that doesn't break the bank.
My problem is, i can't see the sense in replacing something that i can't fault. |
Could you describe what carb problems you encounter? Like "it doesn't pick up well, but when I put the choke on it does better (or worse)" Or: " erratic idle, when I very gradually open the throttle it suddenly gets better at 4.000 rpm".
Try to discover when and where on the rev counter scale it does what, when it gets erratic use the choke to see if it improves or gets worse. Does it get better when you open the throttle fast or when you open it very slowly. Write it down and try to find connections. Or share t with us.
You'll discover if it's really the carbs acting up or still an electric fault. Have you checked the ignition pickps' and coils resistance according to the manual? A faulty pickup (or one with a wrong air gap) will cause erratic running too. Also an stroboscope neon light checking the ignition with the markings on the flywheel will show up erratic ignition too. It did on my db4 when I was fault finding.
Anyway: replacing the 38mm BDST Mukini's (even if these are perfectly in order) by a bank of 40mm TDMR Mikuni's will definitely improve engine behaviour. |
Since i've owned the bike it's run poorly but also run really well. I can't explain why it runs good sometimes and bad other times. When it decides to play nice and run good, it runs really good. No missing or backfiring and even idles fine. It will run nice like this while out on a ride, then the next time i ride it, it plays up.
This time it's possible that it's a different problem as since i've put the new seal kits in the carbs the front cylinder won't fire. There is definately spark, when i remove the plug and earth it it sparks fine. There's also fuel in the carb bowl. Brand new plugs and i've tried swapping them. The rear cylinder fires but front doesn't. The carbs are built the same and set up the same. Airbox on or off makes no difference.
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'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 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, '89 ZXR750, '91 Ducati 851 |
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deebee4
Joined: 08 Jan 2011
Posts: 266
Location: Netherlands
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| Posted: Mon Jun 23, 2014 6:37 pm Post subject: |
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| brian wrote: |
Since i've owned the bike it's run poorly but also run really well. I can't explain why it runs good sometimes and bad other times. When it decides to play nice and run good, it runs really good. No missing or backfiring and even idles fine. It will run nice like this while out on a ride, then the next time i ride it, it plays up.
This time it's possible that it's a different problem as since i've put the new seal kits in the carbs the front cylinder won't fire. There is definately spark, when i remove the plug and earth it it sparks fine. There's also fuel in the carb bowl. Brand new plugs and i've tried swapping them. The rear cylinder fires but front doesn't. The carbs are built the same and set up the same. Airbox on or off makes no difference. |
Well this really looks like an intermittent electrical problem. Good thing you know it's the front (horizontal) cylinder that's acting up now and then.
And when it's acting up it's hard to persuade it to run fine again.
How much we feel this must be Italian temperament this is just mechanics.
I suspect one ore more of these possible causes:
- faulty pick-up horizontal cylinder: use multimeter and measure resistance (Ohm) in the connector after taking off the kokusan ignition advance box.
- faulty kokusan ignition box. These can break down, a former track buddy with his 900SS had a faulty one. You wrote you swapped them when it still was running bad. Did you check if it was still the horizontal cylinder that was running badly or was it the vertical this time? You can check the kokusan boxes too with a multimeter.
- ignition coil: there might be a bad connection in the spark plug wire connector or one of both terminals are faulty. Take them off, clean and inspect, measure too with multimeter and if it looks OK refit/swap. Best thing is to just swap every component one thing at the time (coils, ignition boxes etc are the same on both cylinders) and ride it and wait/see/hope that the vertical cylinder starts to run bad. Only thing you can't swap are the pickups (leads and the pickups themselves in the lh crankcase around the flywheel).
- Spark plug connector & leads , did you ever change the originals? If no, replace them with a copper core silicone lead and a non resistor type silicone plug cap. After 15 years of age spark plug leads and caps are ready for replacement anyway.
In the end you'll find the faulty component and after replacement the bike will be far more enjoyable 
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brian
Joined: 22 Aug 2011
Posts: 3769
Location: Australia
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| Posted: Tue Jun 24, 2014 11:35 am Post subject: |
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| deebee4 wrote: |
I suspect one ore more of these possible causes:
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Not at the moment. The front cylinder will not fire although it has plenty of spark.
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'99 DB4 #104, '96 SB6 #1165, '94 DB2 J #652, '99 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, '89 ZXR750, '91 Ducati 851 |
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SpikeC
Joined: 20 Aug 2013
Posts: 450
Location: Portland, Oregon
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| Posted: Tue Jun 24, 2014 5:08 pm Post subject: |
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The usual advice is to look to where you last were. If the problem arose after working on the carbs, then..................
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Spike C.
Portland, Oregon, USA
2008 Bimota DB5R
1965 Triumph T100SC |
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