Why does my dirtbike kick back nearly every single time I try to kick start it?

Question

I have a 1990 RM250 and almost every time I try to kick start it, it has severe kick back. It does not kick back when I give it a slow kick, but every time I slam it, it slams me back.

It does this when I am holding the throttle and when I am not holding the throttle. Choke on and off, it does not matter.

Also, it started in 1 kick the first time, then became impossible to kick start later. The spark plug was wet with fuel.

Answer 1

Sounds like CDI box is going bad/gone bad.



Inside the box there are semiconductors which control the ignition advance



At low speeds,,timing shifts to very late.

Makes for easy starting and "no Kickback"



Then as engine rpms increase,,timing begins to shift towards increasingly advanced.

Eventually it reaches the proper full Advance point for running full throttle.



As the Engine Revs BEYOND that point,,,,,the electronics begin to reverse the Timing advance,,,and goes Back to very late timing.

That action forms an Electronic "Rev Limiter"



That part of the CDI box is a sorta "subsection" added onto the main circuit.

It's connected internally to the power input from the flywheel.



Honestly,,on your particular CDI Box,,,,I do not know this for a fact.

I dont know how the circuit is built Specifically.



But Generically,,,CDI's can fail several ways in their electronic advance.

*Fail in Full Retard mode

*Fail in Full Advance mode

*Fail in an Open Circuit mode,,,where the Advance Circuit takes itself completely Out of the total circuit----acts like it has NONE

*Or,,they can fail Short,,,Dead Short or Faintly,,,Hi Resistance short



---because its connected to Mag's Power wire,,,it can bleed power or Block it from the Box.

Spark goes very weak,,,or sometimes altogether Dead



I cannot say for 100% certain your CDI is headed south,,,but it sure sounds like a good possibility

Answer 2

Before you give it a full kick just lightly move the kick start lever (you might feel it better using your hand, but eventually you can do it with a foot) until you feel piston is at the top of the cylinder, then take it a gnat’s past that point, let the kick start return to vertical and give it a good solid kick. If you have got it right it will start up (if you have got it wrong it will catapult you off the bike).



Some bikes do get difficult to start once they are warm, I have never found a reliable way of starting them apart from patience followed by blind rage, swearing and tears.

Answer 3

Possible pre-ignition.

Remove the cylinder head and inspect for excessive carbon build up on top of the piston and the combustion chamber of the head.