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Author Topic: Carb size on 836 (Revised)  (Read 3749 times)

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Offline solo 2

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Carb size on 836 (Revised)
« on: November 08, 2011, 05:46:31 pm »
I was wondering if mikuni VM33 carbs would work well with this set up, going to be a street bike.

JE 836 piston kit
Dynoman 315 cam
Ported head
lightened crank, Super rods

Would I lose too much bottom end with this size of carbs and are VMs good on these bikes. Thanks, hope this is in the right area.
« Last Edit: November 17, 2011, 04:24:05 am by solo 2 »
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Offline solo 2

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Re: Carb size on 836 (Revised)
« Reply #1 on: November 17, 2011, 04:41:35 am »
I'm building the engine above and I am interested in using non stock carbs of a larger size to get a little more performance out of it and have questions. I would like to keep as much low end grunt as possible but give it the air it needs up top, I realize its a balancing act and involves alot of tuning. I'm seriously looking at going with a larger set of CV carbs and have only seen 1 bike here with this set up (Goldie). Are 32mm a good size, would 34mm be too much. I think larger CVs may give the best drivability traits while giving it the air it needs, please feel free too chime in with your thoughts/recommendations.

If you take newer CVs off a bike with the same or close displacement and horsepower shouldn't they work or be closely tuned? A newer nighthawk 750 has about 75 horsepower with 34mm carbs. I realize it has 4 valve heads and there are many variables, but how close would they be.
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Offline turboguzzi

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Re: Carb size on 836 (Revised)
« Reply #2 on: November 17, 2011, 05:45:43 am »
you cant compare diameters of CV's to slide carbs,

according to john Robinson's book, a CV should be bigger by 20% than a slide carb to deliver the same flow (though he is not clear if its area or diameter)

I am running now CR29's on a 810 cc four (kawi 750 based, but two valve) that's got a full road race tune and they let the motor breath up to 11K pretty good,so  might go up to 31's next season only if money allows, but definitely not very high on my wish list

33VM's would work well on a full liter bike but way overkill on an 836 IMHO, specially if you want to keep it torquey/streetable.

TG
« Last Edit: November 17, 2011, 05:48:56 am by turboguzzi »
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Offline Sam Green Racing

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Re: Carb size on 836 (Revised)
« Reply #3 on: November 17, 2011, 06:41:55 am »
31mm is plenty big enough for normal carbs but 34mm is ok with CVs.

Sam. ;)
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Offline solo 2

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Re: Carb size on 836 (Revised)
« Reply #4 on: November 17, 2011, 05:08:32 pm »
Thanks for the replies, answered what I wanted to know. Has anyone tried or thought of using FZR600 carbs, they are 32mm flat slide CVs. Might work well.
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Offline Bill/BentON Racing

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Re: Carb size on 836 (Revised)
« Reply #5 on: November 19, 2011, 07:04:42 am »
Samauto has CV carbs,32mm,off a late model GS750 @ 88-89.Once dialed work pretty damn good.I think Calendar Girl wants something different for next year.......Frank got the Webers and Jim my 29's! Dumbazz me! ;) ;D Bill
But Mike Rieck has some RS34's and that 1000cc APE kit might have to come off the shelf....along with Mike's head.
Good Luck,keep us posted ,you'll like that 315 cam. 8)
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Offline jweeks

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Re: Carb size on 836 (Revised)
« Reply #6 on: November 19, 2011, 07:29:20 am »
Seca 32mm CV's or Canadian Nighthawk 750 34mm CV's are supposed to be bolt ons. You'll probably play with the main jets, but the results should be very smooth.

                                                               Jon Weeks
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Offline dragracer

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Re: Carb size on 836 (Revised)
« Reply #7 on: November 19, 2011, 08:07:14 am »
Quote from: JWEEKS on November 19, 2011, 07:29:20 am
Seca 32mm CV's or Canadian Nighthawk 750 34mm CV's are supposed to be bolt ons. You'll probably play with the main jets, but the results should be very smooth.

                                                               Jon Weeks

Jon, i know you post this before but what type/size carbs do  you have on your dragbike??
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Offline jweeks

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Re: Carb size on 836 (Revised)
« Reply #8 on: November 19, 2011, 09:16:15 am »
34mm Mikuni CV's. May go to some 36's when I stroke my 900F crank some more. It was discussed with Jay at APE last weekend.

                                                                      Jon Weeks
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Offline solo 2

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Re: Carb size on 836 (Revised)
« Reply #9 on: November 19, 2011, 04:37:53 pm »
I've got the old set of 34mm from my 81 Gs1100, has rs36s now, would have to re-space them though. What about the inlet sizes, what would one do about the intake rubbers, does someone make larger sizes or can you mod them.
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Offline Retro Rocket

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Re: Carb size on 836 (Revised)
« Reply #10 on: November 20, 2011, 12:42:56 am »
Quote from: solo 2 on November 19, 2011, 04:37:53 pm
I've got the old set of 34mm from my 81 Gs1100, has rs36s now, would have to re-space them though. What about the inlet sizes, what would one do about the intake rubbers, does someone make larger sizes or can you mod them.

You can buy inlet rubbers that fit the Suzuki carbs to the Honda 750, i have a set but they bare not for sale by themselves, they go with a set of CR31's that are racked to suit the GS1000, 1100 Suzuki and Z900, Z1000 Kawasaki's.
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Offline solo 2

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Re: Carb size on 836 (Revised)
« Reply #11 on: November 20, 2011, 05:18:42 am »
Quote from: Retro Rocket on November 20, 2011, 12:42:56 am
Quote from: solo 2 on November 19, 2011, 04:37:53 pm
I've got the old set of 34mm from my 81 Gs1100, has rs36s now, would have to re-space them though. What about the inlet sizes, what would one do about the intake rubbers, does someone make larger sizes or can you mod them.

You can buy inlet rubbers that fit the Suzuki carbs to the Honda 750, i have a set but they bare not for sale by themselves, they go with a set of CR31's that are racked to suit the GS1000, 1100 Suzuki and Z900, Z1000 Kawasaki's.

Where would I find a set of these rubbers. I've read that F2 boots are larger but have really not seen anything concrete on this subject, and I do alot of searching. I've seen boots that fit the VM29 but can't find the spigot size of those carbs anywhere. Obviously I'm missing something as others have done this mod, the spigots are 42mm OD on the 34mmCVs.
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Offline bwaller

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Re: Carb size on 836 (Revised)
« Reply #12 on: November 20, 2011, 07:23:57 am »
Th VM29 spigot OD is 34.2mm.
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Offline turboguzzi

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Re: Carb size on 836 (Revised)
« Reply #13 on: November 20, 2011, 10:09:53 am »
re-spacing any rack of OEM CV's or even OEM slide carbs is going to be a HUGE challenge

OEM's are not like CR's or other racing carbs racks where re-spacing-ability was built-in to begin with

you'll have a much easier time accepting the OEM spacing (assuming its in the ball park) and building one-off manifolds to fit between ports and carbs.

IMHO at least... 
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Offline solo 2

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Re: Carb size on 836 (Revised)
« Reply #14 on: November 20, 2011, 12:24:11 pm »
I'm a machinist so doing stuff like that is just another challenge to overcome, but I'm also incredibly lazy ;D so if there's an easier way of doing something, I'm in. I'd really like to find out how other people who have done this mod went about it, after alot of reading posts the actual how to is fairly vague or non existant.

I'm not afraid to try stuff even if it hasn't been done but it's always nice to have the best starting point that you can, and of course when I do it finally I'll document it fully in my build thread as I like to give back if I can without just repeating whats been done a million times before.
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Offline Retro Rocket

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Re: Carb size on 836 (Revised)
« Reply #15 on: November 20, 2011, 01:59:36 pm »
Try Mark at M3 racing for those inlet rubbers, If he hasn't got them he will know where you can,  he is also a member here, user name "kos".
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Offline solo 2

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Re: Carb size on 836 (Revised)
« Reply #16 on: November 21, 2011, 08:00:34 pm »
After a little more research I think that the 77-78 boots may do the trick as they are supposed to be 2-3mm larger on the carb side.

I'm still really curious to try a set of FZR600 carbs which are 32mm flat slide CVs, should provide great throttle response and good performance. They do however have the 15 degree float bowls on them which could make them alittle hard to set up. I know the GS1100 guys are big on using the 36mm flatslides from the GSXR750 and getting good results, kind of a cheap RS conversion.

Anybody got any thoughts on this set up, good or bad.
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Offline Retro Rocket

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Re: Carb size on 836 (Revised)
« Reply #17 on: November 21, 2011, 08:45:37 pm »
Terry in Australia {forum name} had a set of 34mm CV's off the Aussie model CBX750 Honda, around an 85 model, they had to be re racked, but they worked very well on his 836 and had a very light throttle...
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