Topic: CR carbs v. stock carbs on a CB750...

[Terry in Australia]

Very true Frank, I guess getting the "full range of power" depends on how "Wicked" the cam profile is. My 836cc engine with 12.5:1 comp pistons, MJR stage 3 head and Megacycle 125/75 cam was a pig with 29mm CR's up to 7000 RPM, then it got very "wicked", very quickly.

Great for racing, but in the real world, the mild 836 in my gold K2 with 32mm CV carb conversion would kick it's arse up to racing speeds. My hot  836 is actually much better now with stock carbs. Cheers, Terry.

[Doctor_D]

I don't know what classifies as a pig for you folks clinging to the underside of the earth, but my 836, cr29, 11:1, 125-65, JMR stage 4 head is very tractable.  Had to go to 70mm velocity stacks, 230 main air jets and YY7 needles before the midrange woke up.  As we've currently got it set up, there are no problems whatsoever with lugging from 3k rpms all the way past redline.

On Twinline's rather conservative dyno, it was making 40 lb/ft of torque at 3k, 50 by 4k, nearly flat to the current peak of 51 at 6k, and hanging on at 50+ all the way through 9k rpms. I will admit to being pleasantly surprised at the low end torque given the completely open 4 into 4 cr-replica exhaust, but that speaks to the power-band broadening effect of looooong, tapered reverse-cone megaphones. Mike's superb head-work probably had much to do with it as well.



Next up I'll be giving a 125-75 cam a try.

[cbrfunk]

points taken. thanks David. sounds like it's all about the set up. will have to do some trial and error. anyone have experience using them on an F2 head?

chris

[Terry in Australia]

I don't know what classifies as a pig for you folks clinging to the underside of the earth, but my 836, cr29, 11:1, 125-65, JMR stage 4 head is very tractable.  Had to go to 70mm velocity stacks, 230 main air jets and YY7 needles before the midrange woke up.  As we've currently got it set up, there are no problems whatsoever with lugging from 3k rpms all the way past redline.

On Twinline's rather conservative dyno, it was making 40 lb/ft of torque at 3k, 50 by 4k, nearly flat to the current peak of 51 at 6k, and hanging on at 50+ all the way through 9k rpms. I will admit to being pleasantly surprised at the low end torque given the completely open 4 into 4 cr-replica exhaust, but that speaks to the power-band broadening effect of looooong, tapered reverse-cone megaphones. Mike's superb head-work probably had much to do with it as well.



Next up I'll be giving a 125-75 cam a try.

Yeah mate, your setup is similar to mine, except for the cam. A 125/65 is a much better "all round" grind than my 125/75. Mike recommended the 125/75 when he did my head, but in hindsight, I wish I'd gone for the milder grind. Gotta love that torque, my Triumph Rocket III puts out 147 foot pounds of torque at the back wheel, it's scary fun! 

[gnarlycharlie4u]

Is full range of power & wicked cam, even Allowed in the same sentence..

sure:

You'll probably never see a full range of power with a wicked cam. haha