Topic: Choice of carburettor for 500 Racer

[DresdaHonda]

In a cb550 BE with cb500 cylinder and cb650 head, (mayby with a webcam)
What is a cheap choice of carburettor ? -cb750 cabs ? model and setup ?
and do I need the plate (betwen head and cabs) that`s push/pull ? -or is there a nicer way
What throttle with push/pull is used for racing?
Peter


 

[Bill/BentON Racing]

One way would be to use 69 CB750K carbs with 4-1 cable.You can pull slides and change needle position much quicker than linkage set up.No push/pull though.Big performance increase; 22mm's vs. 28mm's! Lots of other choices up to @ $2500.00.If you need a set of 69's let me know. Good Luck,Bill

[DresdaHonda]

I like to see this 4-1 cable, before I use 2 cable throttle spit to 4 cable and that went wrong
maybe because of a little difference in springs, in cabs ??
-Where to bye new springs ?
I have some CB750 cabs, but don't know what year they are from, I think it's keihins 29mm
-have to pick them up at my workshop and take a look.
What about jetting ? -any Suggestions

Peter

[DresdaHonda]

I'm not sure if they are for a 69 CB750K
Its 29mm Keihin

Peter

[Bill/BentON Racing]

They have screw on tops like '69's.Sure they aren't 28mm's? What is the carb model # on body? B750A I found on the mounting plate...nothing on carb bodies on the '69's I had. Do you have a plate or #'s on carbs? Bill

[DresdaHonda]

Yes, there have to be a plate behind, but used them without and used cabels.
-Mayby it´s 28mm, bore 1mm ??

Is mikunis better ?

Peter

 

[turboguzzi]

keihin CR29's - expensive
Mikuni VM28SS rare & expensive
cb750 28's - affordable
Mikuni VM26 (27 in reality) EX GS750, KZ750, etc. cheap and easy to find

I used the VM27's i bought at a swap meet for 50$ for two seasons and they werent bad at all, 61 rwHP with them. good value for money. moved now to CR29's, they might be worth just a few hp up high the rpm. they defientely look the biz, so if you have the money to burn....

TG

[Rick4004]

I am now boring carbs for the 550

 see services section http://forums.sohc4.net/index.php?topic=76084.0

Rick Denoon

[turboguzzi]

hei rick

love your cb400/vf500!

nice work,

considering the cheapness of VM26's (actually full round 27mm) and how they give you a straight shot with the 500 cylinder spacing, I think your boring is a really good idea for those who want to keep the stock aribox and looks, less so for all out racing like Dresda wants.

check it out

http://forums.sohc4.net/index.php?topic=19554.0

TG

[DresdaHonda]

Hello Racers

So I bought some vm26 mikuni´s cheap (from a old z1 or z900)

Do anyone have some idea about the jetting ?

Thanks
Dresda

 

[turboguzzi]

ended up with 135-140 jets on those carbs but you will definitely want to have a nice range in your toolbox to see what works best for your motor setup, say from 115 to 150 in steps of 5. BTW, dellorto 6mm jets work fine on these carbs, much cheaper.

Try to spend some time on the dyno, picked there 5hp "for free" just with jetting.

TG

[DresdaHonda]

Thanks TG

I'm gonna looking for some jets.

-What about the connection, I know it is needed to make some tubes to connect the vm mikunis to the head, but what about the "backplate" on the vm mikunis, it make the cable push/pull on the right place ?

Think I have seen some pictures here but not sure if it was vm or Cr mikunis.

I like to make some downdraft (around 10 deg.) Is the vm mikunis OK for that ?

Dresda

[turboguzzi]

leave that backplate in place, that's what holds the carbs together. You might have to modify the area where the push pull cables attach as they might hit the frame. after installing them you will see what i mean

you will indeed have to make custom manifolds to fit the VM's, dont think you'll find anything off the shelf. it can be simple ones, done on a lathe, but no downdraft.

to get any downdraft you will need to cut them at an angle. I did it, but it was quite tricky. I designed the cut angles on CAD but regretfully, lost those files.

Take into account that the VM spacing doesnt exactly match the ports, again, no easy solutions.

my VM's worked fine with 10 degs downdraft, so did the CR i used later

TG