Dirt bike kickstart question

Question

I ahve recently bought a kawasaki kx450 and i want to be able to really look after it (its my first new bike) so im trying to improve my mechanical knowledge!

With a kickstart, when you move it down it suddenly goes from loose and easy to push to really hard, initially i always thought this was the ratchet system of the kickstart starting to move the piston up/down. But i was informed that its actually starts moving as soon as you move the kickstart down and that its actually the gas and air mixture compressing in the cylinder right? So once it starts compressing and gets hard then generally you move the kick lever back to the top so you can get a full kick on it. so why is it that once the cylinder is compressing the air and gas and you move the kick lever to the top its not hard to push down straight away? Even tho where it gets hard to push is slightly higher its still not at the top. Why is that?

Solar Mike · Answer

The initial part of the movement is to engage the mechanism, once it gets harder to move then you are starting to move the piston.

oryades · Answer

Virtually all dirt bikes have some sort of decompressors on camshaft, and most of them have auto-decompressor, which acts below certain RPM. So when you kick slowly, it will keep valves open, so that it's easy to "prime" it. When you do hard kick, then you are exceeding minimum RPM, and auto-decompressor stays close and you can start the engine.

I don't know how it is on KX450, but on Honda dirt bikes you can kick forever without resistance if you don't kick hard.

Dirt bike kickstart question

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