just put a bolt on k&n air filter, do I need to change jets? isn't running properly, nearly cuts out on idle.

 

There is a rubber hose that usually goes into the bottom of the air box which needs plugging with a screw when you install a bolt on k&n filter.

 

Check that the nuts/bolts fixing the carb to the manifold are tight.

I remember for some reason they used to come loose on them and cause that problem?

 

I'm sure with my old xr3 u got a different carb jet with it too in the kit? Also I think the breather pipe went into the bottom of the filter in a hole. After I fitted them I set it up on the gas analyzer at work for the fueling