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Old 04-12-2013, 06:37 AM   #14341
bluesman
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Ladder106,
Thank you.

What makes me think different about Dakar bikes - here is it...my take - I could be wrong.
All of DR Zetas build by same team, but not same years - they all run those CVT carbs. Initially looking at front forks from DR350 on Zeta I thought "OK, there was no carbs or forks choice" - but no. I was wrong. It was all there.
Then I found reason for forks (weight - Zeta was stripped to bare mininmum) but they kept on using same carbs. And the kept boring them out and getting more BHP.
This leads me to conclusion, that 60-65 bhp achievable with stock carbs and about same with pumpers at no harm to motor.
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Old 04-12-2013, 07:28 AM   #14342
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Blue , that's a funny point , too sensitive no no not at all it depends on how much you screw the throttle , like any bike, I ride my yellow bike on some fairly rough steep terrain and do not have any trouble at all to being to sensitive .
Now here is the reason, quite simple really use the stock hand throttle and single cable set up , also just move the return spring to the soft position there are 3 to choose from.
some other things to do like I did was to aim the pump squirt jet at the needle to dissipate the fuel instead of one great dump of fuel.
The other thing I did but this was on the motard was to adjust the pump squirt timing, only takes a couple of minutes to do one small screw on the nylon bit at the top of the pump rod I set it so it worked a bit later for the roundabouts and not so sensitive , I did this when I had the quick action Domino throttle.
I never really liked that domino set up and went back to the standard single cable on the motard.
OK on the orange bike, I ended up using the Domino that I took of the motard, but used a different DIA twisty part some may call it the twist grip, the bit that turns and the cables go into, it was smaller than the Domino DIA but larger than the DIA of the standard Suzuki one, it was some after market job for a dr 400, it fitted straight in I also set the spring return tension to the lightest setting or the middle one carn,t remember now a few years back, this was and is a happy medium set up.
Now with pumpers you don,t need a air box at all ,its only there for keeping dirt and water of the filter, this was a big improvement over the airbox , I could feel it through my arms there is no flat spot or hessition any where and very happy with the out come I also went larger on the mains than what they arrived with.
So there are many variables to try that some not meening you at all have not yet tried and winge about, maybe your mate then .
Allso every body has there own personel prefrences and what I have done may not suit them or a just to silly to try something different or may not have the knowledge to start with.
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Old 04-12-2013, 07:38 AM   #14343
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Now Dakar bikes and so called upgrades to SR/ 43,s don,t get me started very sensitive to this one watch out ..
I did wright a full page on this about 2.5 hours ago and bugger me must have hit the wrong button or something or was it when the mouse decided to drop on floor and lost the lot of it to the universe or where ever it goes.
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Old 04-12-2013, 07:39 AM   #14344
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OK, too sensitive to trottle idea out of window then. Back to square one.
E.g. Zeta used CVT carbs with 60-65 bhp and modified airbox with no issues.
Reason for using CVT carbs - unknown, but perhaps - they can do the job just fine?

Rob, I completely trust you feeling of your bike, but I do have my doubts about no airbox. I did not have bad experience with DR and pumpers and no airbox, but had it with other bikes with similar setup. I leave it as open question to anyone and first of all Derek (if he don't mind), who is definitely resident guru in this stuff - I am not arguing it. But to me idea that it does not need airbox because of pumpers does not really click - no more than my personal thinking, not arguing.

I also remember someone in tread trying open filters with pumpers and getting surging at high speeds because of turbulence.
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Old 04-12-2013, 09:06 AM   #14345
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I may have to lay out the brass for those carbs once I get the SR41 engine rebuild.....just 'cause they are so darned PRETTY !
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Old 04-12-2013, 09:54 AM   #14346
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Quote:
Originally Posted by bluesman View Post
Reason for using CVT carbs - unknown, but perhaps - they can do the job just fine?
With an slide carb you are stuck, for a given throttle position, with whatever shape of fuel delivery curve you have, i.e. if you have some lean areas at some rpm and some rich areas at some other rpm, that cannot reasonably be fixed. In most cases all that can be done is to move the entire curve up and down, i.e. add or subtract fuel for the entire throttle position. If you add fuel, you will fix the lean areas, while making the richer areas worse. If you subtract fuel, you will fix the rich areas while making the lean areas worse. In some cases you can cant the entire curve (i.e. tilt one end up or down). This would be via a dam at the needle jet outlet (a la Keihin CR) or via air correction on carbs equipped with emulsion tubes (a la some Mikuni VMs and some TMs).

With a CV, since the slide height, and therefore the needle height, are velocity, and therefore rpm dependent, you can, within limits, address separate rich and lean areas for a given throttle position via needle shape.
Quote:
Rob, I completely trust you feeling of your bike, but I do have my doubts about no airbox. I did not have bad experience with DR and pumpers and no airbox, but had it with other bikes with similar setup. I leave it as open question to anyone and first of all Derek (if he don't mind), who is definitely resident guru in this stuff - I am not arguing it. But to me idea that it does not need airbox because of pumpers does not really click - no more than my personal thinking, not arguing.
I agree that a pumper carb does not negate the need for an airbox. However, there can be gains from modifying or removing an airbox. Often airboxes would need much more capacitance to help power (which there is often not real estate available for). When you can't increase capacitance, then the only alternative is to reduce resistance. That is why removing the snorkel, otherwise opening the airbox or removing it can help. However it brings with it the risk of making a mess of a formerly flat CO trace.
Quote:
I also remember someone in tread trying open filters with pumpers and getting surging at high speeds because of turbulence.
It's best if the carbs can draw from air that is as isolated as possible from the effects of air blowing over the bike at various angles.

Regards,

Derek
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Old 04-12-2013, 09:54 AM   #14347
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Originally Posted by Ladder106 View Post
I may have to lay out the brass for those carbs once I get the SR41 engine rebuild.....just 'cause they are so darned PRETTY!
Keep in mind the heavy throttle pull.

Regards,

Derek
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Old 04-12-2013, 03:56 PM   #14348
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I read some where probably on here that the or one of the Dakar bikes used a 110mm piston, at a guess maybe around 50 extra cc or so, this would make up a lot of the extra HP one would presume,
thoughts .
Ray you may have hit the nail on the head when you said economy for Dakar bikes, pumpers in the off road race mode of things do use shed loads , how ever on road I meen flat open boring roads I get better economy 20.5kpl .
you can get down to 11kpl on track trail riding if you give it to it all the time eg 606 worn half way down in 253 klm,s .
This meens if play you pay.
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Old 04-13-2013, 03:22 AM   #14349
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Quote:
Originally Posted by MrPopples View Post
Guys ... I need help, I can't keep my mind off the Mikuni flatside kit ! ( http://www.dr-big-shop.de/BIG_MotorTuning_140.html )
I keep thinking about it ... I KNOW it's too expensive, 600 euros is twice the price I could get if selling the bike today ... but damm, I want it so bad ...
HERE are a couple of pic,s I did with my orange bike, I did cut the triangular piece out of the standard air filter and tossed the snorkel, some have done ONLY this and have trouble with the standard carbs with side winds etc, I am using the TM 36 carbs, the ones you Want .
I allso did this which also may stop that side wind effect as I don,t suffer from it at all and have done many trips on this bike, about 12k so far after the modification , the bike goes good and happy that I changed the carbs .
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Old 04-13-2013, 03:24 AM   #14350
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Old 04-13-2013, 03:25 AM   #14351
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Old 04-13-2013, 03:28 AM   #14352
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this should have bee first
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Old 04-13-2013, 03:32 AM   #14353
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And one for Ray, he likes looking at em,
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Old 04-13-2013, 07:27 AM   #14354
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Bike Porn......nice
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Old 04-13-2013, 10:03 AM   #14355
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Originally Posted by robmoto View Post
I read some where probably on here that the or one of the Dakar bikes used a 110mm piston, at a guess maybe around 50 extra cc or so, this would make up a lot of the extra HP one would presume,
thoughts .
Absolutely. But it also means that carbs coped just fine with considerably increased flow of ...well...everything. Those bikes had massive airboxes and took quite some fuel. They had cc increase - yet those carbs still managed to cope. I mean - I can't argue with Derek on CVT vs. pumpers operation because not only trusting his summary - in any case this is exactly same with what I know and learned (from my both bikes experience and my education etc.). E.g. if we pull all together it seems carbs are not limiting factor in BHP figures on DR, but more of factor on trottle reaction - at price of fuel.
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