Topic: Seeking Carb recomendations, '76 CB750f, 836, CX1 cam, 4-1 yoshi repro pipe

[rangerdave1]

I am seeking recommendations on which carbs to use for a '76 CB750. I have a 836 flat piston kit, CX-1 cam, and a reproduction Yoshimura 4 in to 1 pipe.

I would like to get what potential power is available with my setup but don't want take out a second mortgage to do so... I have a couple other bikes which are much faster so I can sacrifice some power for the right price providing it will be a reliable setup. 

I would like to get a set of Keihin CR carbs like I have on my GS1000 however since I live in Canada, the exchange rate makes it very expensive. At around $1200 US, it brings the price to about $1700 with shipping.


What have others been using on a similar build???

Are there stock carbs which can be adapted for my setup? Should I just use the stock carbs and re-jet them?

Any advise is appreciated.

[gschuld]

http://forums.sohc4.net/index.php/topic,158461.0.html

You should check out what Matt has been able to do with stock round top carbs on his sportsman class road race bike.  I’m thinking you might be quite impressed with what round top are capable of.

CR carbs, smoothbores, RS series carbs, etc are all high quality carbs, but up to a respectable amount of RWHP( up to around 80 or so), factory round tops have shown to be up to the task.

George

[PeWe]

Head is not ported?
If not, stock carbs are definitely OK. OK anyway.

I used my CB750 K6 stock carbs with 836, ported head, 34mm inlet valves, Action Fours SS-1 cam (0.360 lift, 21/53, 54/22 @ 0 lash 0.04" lift)
Lightened alternator rotor helped to rev a little bit quicker.

Stock carbs were OK. Pods, stock pilots, needles 1 step richer. Mains were +140. Rather open 4-1.
It did not run slower than with Mikuni Smoothbore 29mm that had crappy cracking boots.

[rangerdave1]

The engine is not built yet so I'll likely port/polish the head and see about doing the valves. Not looking to go crazy with this engine, just wake it up a bit.


I'll look at doing something with my stock for now but I was hoping there was a common OEM carb swap for older CB750s...

Do the stock carbs accept pods or velocity stacks well?

[slikwilli420]

Mine runs aces on velocity stacks and sock filters.

[calj737]

Mine runs aces on velocity stacks and sock filters on the track.

[slikwilli420]

Mine runs aces on velocity stacks and sock filters on the track.

Runs fairly strong down low, and I would attribute any lugging more to cam than carburation. My carbs are totally stock and the velocity stack I use approximates the stock ones in the air box. The filter is just there to keep crap out of the engine during any off-track excursions.