Hitchcocks Forum

Has anybody out there found that the kickstart ratio is such that with the close ratio gearbox the kick start lever needs to be longer , my bike is a pig to start with the new ratio , the gear is smaller than standard , even bump starting needs far more speed with my extra tooth front sprocket , in trying to emulate a Gold star box ratios and I gave myself a new problem as I only weigh 9 stone and I've tuned the engine with 9:1 comp ratios , I might need a speedway bike starter !

My bike had the closer ratio gear set fitted when I bought it, and it has a 625 conversion with about 9:1 static compression ratio, so I just got used to it!......However, by one tooth larger front sprocket, do you mean the gearbox sprocket or engine (crankshaft) sprocket? A variation in gearbox sprocket will make no difference to the kickstart ratio, although it would affect bump-starting.

Forgot to mention, but using the decompressor makes starting easy enough. I just wish that it was a proper valve-lifter, rather than a problem-prone additional miniature poppet valve.....Has any engineer out there worked out how to modify the exhaust rocker cover to accept a valve-lifter assembly from anothe bike?....That would be a nice addition.

If you use the right method it souldn't be a problem. http://www.whfolk.co.uk/REOCHUMBER/Arti ... arting.htm

I must re-learn a method of kick starting , I'm kinda kicking myelf for welding up the de-compresser exit port and fitting a blanging plug , the head was ported and I cant see the weld but the de-compresser is a horrible design and a real valve lifter would be best but thats the Bullet for you . I can now see why the rear hub with detachable sprocket for quick rato changes would be right for me , with a now very tall 1st gear and 1 extra tooth on the final drive front sprocket spinting through Sydneys stop start traffic is harder on the engine ( more clutch slip )so a bigger rear spocket for city use and smaller for Australian inter-city long hauls . The high lift cams have made the engine come to life with the 535 piston , it will be intresting to see what my fuel consumption is now .

Hi Another Alan. If Phil has fitted the close ratio, then the 1st gear (also the kickstart gears) have changed from 2.78:1 to 2.5:1. The large combined "high gear kickstart pinion" is fitted on the Layshaft and since the gears are used in reverse when the kickstart is operated, you can see by reversing the shown ratios, the mainshaft/clutch/engine will be turned over at around 11% more slowly by the kickstart.

Les, I hadn't done the maths but 11% seems right. This should make it easier to kick as you have more advantage. It also means that one stroke of the K/S turns the engine 11% less so it's even more important to start the kick at the right position and follow through right to the bottom.

Hi Les, thanks for the clarification (and apologies to Phil for my error) regarding the effect of the closer ratio gears.....However, I still don't see how a larger gearbox sprocket affects the kickstart ratio, or has Phil fitted a larger engine sprocket?

I've just re-read the whole post, and it makes sense to me now....I promise to pay more attention in future!

Hi Pete and Allan. Yes, you deffinitely need a decompressor, on a high comp single especially. Pete is right and it will be 11% easier (lighter) to kickover, but it is speed that important as you are kicking down ATDC with no resistance anyway, and trying to store energy in the flywheels so they whip the piston up to compression. The Velo Venom is known for being difficult to start and has a similar low kickstart speed this is said to be a big factor for that.