Author Topic: How much power is too much for K0 carbs  (Read 1601 times)

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Offline gschuld

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How much power is too much for K0 carbs
« on: February 09, 2013, 06:54:48 AM »
So for a visual example, and who doesn't like dragbike pictures, Action Fours famous "2x4" twin engine dragbike (the color photo is on the magazine cover 1972) ran clearly K0 carbs.  Most photos I have seen show the early Honda dragbikes running RC inspired Weber setups.  Based on sheer numbers, the Weber carbs very likely had the most speed potential.  But it appears that the K0s on the Action Fours bike were keeping up with a pretty respectable amount of power to be as competitive as it was early on.

RC Engineering in the earliest days, ran with retuned factory carbs until he went down the weber path(and Hillborn injection).  Reportedly, some of the earliest Cobra engines used retuned factory carbs as it was the only option available. 

So the question is...  At what point does the K0-early 70s type carbs become the major restriction in a significantly hot-rodded 750 motor.

As a practical example(mine ;)) a 1000cc RC Engineering built 69 Diecast motor. RC ported heads, RC HD Springs, RC aluminum retainers, lightened and polished rockers, 1mm oversize intake valves, lash caps, and  likely a change to either an RC #295 or #315 cam.

Is it fair to say that if the Action Fours dedicated (and successful) dragbike ran well on K0 carbs, my undoubtedly lower power output motor should run well on them as well?   Not to delute the apple to apple comparison, but it is certainly possible that the K0 carbs on the Action Fours bike could have been custom bored to a larger throat, a popular racer trick back then.

George

Offline 754

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Re: How much power is too much for K0 carbs
« Reply #1 on: February 09, 2013, 08:23:19 AM »
 They ran KO carbs out of necessity..

 The only reason I can see to run the 295, is maybe touring.
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Offline Don R

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Re: How much power is too much for K0 carbs
« Reply #2 on: February 10, 2013, 12:36:04 AM »
Looks like they were connected by the primary chain. wow.
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Offline Retro Rocket

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Re: How much power is too much for K0 carbs
« Reply #3 on: February 10, 2013, 01:10:04 AM »
Didn't they bore the stock carbs out..?
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Offline cbr954

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Re: How much power is too much for K0 carbs
« Reply #4 on: February 10, 2013, 06:50:04 AM »
Action Fours engines most of the time were not larger than 836 either, they didn't like the really big stuff.  I have that magazine somewhere but now when I want to look through it I cant find it!
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Offline gschuld

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Re: How much power is too much for K0 carbs
« Reply #5 on: February 10, 2013, 11:17:12 AM »
Action Fours engines most of the time were not larger than 836 either, they didn't like the really big stuff.  I have that magazine somewhere but now when I want to look through it I cant find it!

Funny you should mention that.  My "Motorcycle Drag Racing: A History" book by John S. Stein just arrived in the mail this morning.  According to the book, The Action Fours "2x4" twin   "featured engines bored to 785cc, 12.5:1 pistons, and Kenny Harmon "F" grind cams along with stock carburetors, clutch, and transmission."

Don R      ...one for you    "Rather than coupling the engines with a chain between the ends of the crankshaft as everyone else had done, or using a rubber belt as others would soon do, the machine ran a chain from the crank centerline of the front engine to the rear."

"At the Hot Bike Magazine/NHRA Nationals in 1972, rider Hahn made a 9.57 second run at 148.53 mph ----four-tenths and eight mph faster than the existing record." 

Unfortunately, no mention at whether the K0 carbs on the Actions Fours bike were bored or not.

George