CB engine rebuilt, new cam chain, valve timing set, clearances at 2 thou, ignition timing spot on. Fuel on, tad of choke, ignition on, kick - fires first swing, marvelous. After initial warm up run of five minutes we cut the ignition and went over the engine looking for leaks and loose bits. Satisfied all's well I took the bike for a blast up the road - at 1/2 throttle it all went horribly wrong - EXACTLY the same misfire as before !?&@?!!$£?@%!. Back to the carbs then. These are 18mm round slide Kehins. Basically at tick over you've got a pilot jet and mixture control to adjust, from tick over to 1/4 throttle the mixture is determined by the shape/size of the cut-away at the bottom of the slide, from 1/4 up to 3/4 throttle the tapered jet needle and the needle jet it slides in control the mixture, from 3/4 to full throttle you're running on the main jet. All these stages are adjustable, plus float height adjustment is critical. Add to this you've more than one of these instruments to synch and you have a rough idea of what's required - PATIENCE. Lets forget about atmospheric humidity, temperature, altitude, pressure etc. The carb parts on the bench are: throttle stop screw, pilot mixture screw, float valve seat, float valve needle, pilot jet, assorted main jets #88,85 & 83, jet needle, needle jet, emulsion tube/jet holder. The mini pocket microscope (50 X mag) is handy for reading jet numbers and identifying wear. Unfortunately ALL of the above parts are subject to wear and, in the science of fuel/air mixing, this wear is ruinous. Off to stock up Yorkshire Gold supplies and try and find some decent Turkish cigarettes. MORE VARIABLES !
News of Chris Carr's record busting last week (367.382mph) caused me to wonder just how far this art can be refined. One of the biggest restricting factors in the battle for two wheeled LSR domination is the very tight space the power unit has to fit in - 28x18 inches by the rules. Power is what's needed, if you reckon on power requirements climbing at the cube of the speed increase sought you won't be far off. So for a 10% increase in speed we need a 33% (1.1 cubed = 1.33) increase in power - this rather crude formula assumes "all other things remaining equal", well of course they don't, developing more power will no doubt require a heavier motor, stronger frame etc etc and a few too many pancakes for breakfast could ruin things. In '56 a streamliner 650 managed a staggering 214mph with an estimated 80bhp on tap (another dirt track rider). Chris's speed last week is near as damn it 71.53% faster than Johnny Allen's 214.17mph - so: 1.7153 cubed X 80 bhp = 403.75 bhp. BUB racing have managed to get 500 horsepower out of this tiny compartment. It is considered desirable to run a "big bang" motor and take advantage of the power pulses, I guess traction is a massive issue given the single tyre footprint and the loose surface. I couldn't resist the photos (robbed from BUB Racing's website). 3000cc, turbocharged, four cam, 16 valve, methanol-gulping V4 producing 500bhp @ 8500rpm - AND - 400ft/lb of torque ! 
Some how the tidy shot of the component parts makes the engineering look very clinical and lifeless in contrast to the shot of the beast assembled and plumbed in - imagine the racket. MORE SALT !
