DOHC Carb Info Needed

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DOHC Carb Info Needed

shinyribs
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I'm doing a little tuning on my '80 and I'm having trouble figuring out what carbs I actually have.

The stock carbs are supposed to be either a VB42A or VB42C.

Mine are VB43D. PO called them "Euro carbs"

I don't know if I can follow and of Dynojet's tuning recommendations since my carbs are not what they're supposed to. And when I google VB43D Kiehin's i come up with nuffin'.

Anybody have a clue on this? Thanks.
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Re: DOHC Carb Info Needed

motogrady


What are you looking for?
You think there may be a bit more bottom end, top end kinda flat maybe?

As far as the euro thing, got me.
Some of the guys over at dohc.com are pretty good.
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Re: DOHC Carb Info Needed

TOOLS1
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In reply to this post by shinyribs
I think "Euro" means-no accelerator pump. My best suggestion for you would be Mikuni flat slides, or Yamaha Seca carbs.
TOOLS
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Re: DOHC Carb Info Needed

shinyribs
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These do have accelerator pumps. No press in jets though, all threaded. And adjustable needles, too.

The bike wont rev past 7k and it charged / charging well.

Pulling the choke doesn't affect it, so I'm assuming its not lean.

Plugs don't look overly rich, but it had 145 primaries. ! Just swapped those for 120's and gave them a bath. I'll do a test ride soon I hope.
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Re: DOHC Carb Info Needed

motogrady


Wow, 7 grand, that thing should just be coming to life.

Backyard mechanic would go 2 sizes up on the main jets,
see what happens.  Even with the choke thing doing nothing.

Gonna be interesting to see what happens by going smaller.

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Re: DOHC Carb Info Needed

shinyribs
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Well, the FSM calls for 102 stock. 145's are nearly 50% larger which seems excessive to me. The bike gets horrible fuel mileage (IMO) and it's definitely not showing signs of being lean. I think it may be over-jetted.

For stock carbs, Dynojet's Stage 3 kits calls for 126's. I'm not sure if that relates to my funky carbs or not.

I went into the factory tool pouch on this bike to get the plug wrench out (cuz it's awesome) and found a small package. I looked inside and found this set of 125's. Interesting. I figured they were free so why not give 'em a try.
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Re: DOHC Carb Info Needed

Beekeeper
I think I read that the VB43 B were for the CB900 C.    Primary jet 105
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Re: DOHC Carb Info Needed

shinyribs
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That's a start! Thanks for that info buddy!
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Re: DOHC Carb Info Needed

Johnnylevi
yup. Ive got 105's in my 750 and it friggin rips to 11k. I had 115's and it would loose power at around 7k.
1981 SS with Kerker 4-1 exhaust and extremely attractive rider.
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Re: DOHC Carb Info Needed

LukeM
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Had to share this:

These go to 11.

Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.
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Re: DOHC Carb Info Needed

shinyribs
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^^^


The 125's helped out a lot. But it's a touch too lean now. It zips right up to about 9 k then starts to break up. I'm gonna try raising the needles some and go from there. At least I dont have to pull the carbs to do that!

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Re: DOHC Carb Info Needed

shinyribs
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Well, that didn't work. Shoulda listened to Johnny! Raising the needle hurt it. Tank back off again...
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Re: DOHC Carb Info Needed

Beekeeper
You live in the banana belt or what?  There are 5 inches of snow outside, and the high of the day so far is 21 degrees.  Expected to stay like this until some time next week.  I refuse to get out of sight of the fire for the forseeable future.
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Re: DOHC Carb Info Needed

shinyribs
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Over the weekend the temps were anywhere between 20*-55* F. Monday it was raining ice. Today it was 65*F with perfect humidity and no wind.

Mountains are weird.  
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Re: DOHC Carb Info Needed

seestheday
In reply to this post by shinyribs
VB43 are CB900 carbs.

VB42 are CB750
VB55 = CB1000C
VB56 = CB1100F
VB62 = CBX (the inline 6 one)

I don't know about the "D".  Maybe something to do with Euro regulations?
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Re: DOHC Carb Info Needed

shinyribs
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Awesome. Thank you!