Thursday, 17 September 2009

Fine Tuning

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 !


Peter Ashley said...

Blimey. But what a great still life. But where's the Park Drive packet, and one left burning on the spanners?

Toby Savage said...

This sounds serious. One would imagine that if you shoveled loads of highly flamable petrol into an engine it could not fail to go!

Affer said...

Diplo, stuck as I am with an Elefant with EXACTLY the same symptoms, I have huge sympathy for you. And I can't even suggest a source of good cigs either!!