[jejackson]

I am working on an 05 crf 450r for a friend. Installed a new balancer gear and shaft and new piston and cylinder. Now that the bike is re-assembled almost every time I try to kick it from the compression stroke down it kicks back. I am not new to 4 stroke starting procedure. I know that I should kick all the way through. It is so bad that I broke the kickstarter. The bike has yet to fire off. The leak down test was about 14% but since no noticeable air out of the exhaust or intake. I assume that since the rings have not seated yet in the new cylinder that it is just blow by. Timing is good. What is causing the kick back? Any ideas? I don't normally ask for help, but this has me stumped.

[Back2-2]

As long as you a certain that the decompression is set to spec. It sounds like you have checked everything else.
It's just a tight new 450cc of engine trying to be started by a kicker.
I rebuilt my 450 some time back and it is still very "tight". As they say "put some rear into it"

[JimDirt]

I find when the bike kicks back it is usually due to a rich or lean condition .... Try this , when kicking (make sure as you said you know) to give it a full hard kick , BUT , pull the Hot Start Lever in while kicking .... see if it fires up , if it does , I would suspect the fuels screw is out too far , it should be between 1-3/8 to 2-1/8 turns out , or the pilot jet too large for the elevation , (it should be #45) , or the float is set too high (it should be 8mm)

How I start a cold engine is , 6 full twists of the throttle , pull the choke , and slowly kind of gently , kick over the engine a few times till it gets on the stiffest of the compression strokes..... Then give it a like you mean it kick and it should fire right up...... for a warm engine , I get it on the highest compression you can feel as mentioned , then use the hotstart as mentioned , it should fire right up .... but a cold engine , I always find needs about 6 full twists of the throttle before it will just fire right up

Report back with findings ....