Need help on how to lighten spinning mass on 305?

mobilyte · Post by **mobilyte** » Sat May 05, 2012 2:41 pm

i was under the impression that cb and cl cams have different profiles...

Hotshoe · Post by **Hotshoe** » Sat May 05, 2012 10:11 pm

I'd fit a valve spring kit and a set of CB750 carbs. CB750 had the same diameter slides but they are taller, so it's the same size carb at small throttle openings and a bigger carb when you open it wide open(they are oval bores).
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Teazer -
That's a new idea for me, using CB750 carbs on a 305.
I looked at some on Ebay and I see what you mean about the oval shaped venturi.
Is there a model year/K designation that works better on a 305?
I was thinking about replacing the stock carbs on a 337 kitted engine I'm building with Amals, do you think the CB750 carbs would work better?
Thanks, Chuck.

teazer · Post by **teazer** » Tue May 08, 2012 12:12 am

Many Keihin carbs from back in the day had oval bores, or more accurately figure 8 bores. One trick used to be to clean up that center bulge, but the difference is small.

I used CB759 carbs on a few CB77 350s. The motor could possibly use larger carbs, but I got a set of 4 quite cheaply and they were the same design (of the era), so it wasn't too hard to get them into the rules.

The first set I had were from a linkage set (K2-K7 I guess) and I had to modify the top caps to take a cable and the slides to take the cable. Not too much work. K0 cable operated carbs would be ever better. The right tops and slides.

If you can get either early of late at the right price, they are not too bad. On one motor I used a regular Mikuni carb mount on an adapter plate. On others I had inlet stubs machined and welded to the head and use straight radiator pipe. On another I had a stub adapter machined.

Now I'd just use a welded stub. Others use adapters and stock CB750 inlet rubbers.

We had to use those carbs to be legal in Australia or use CR Keihins (above my pay grade).

Hotshoe · Post by **Hotshoe** » Tue May 08, 2012 9:32 am

Thanks teazer.
Very interesting stuff, there's a pile of CB750 carbs in a salvage yard nearby that I never paid too much attention to, might have to go see if I can get a set of K0s for cheap.
If I decide to go that way, I'll PM you with some more questions about installation and jetting if you don't mind, don't want to hijack VOXA's post anymore.