1984 CR250 tuning info

The header is the 1st cone ?
Automatics have longer pipe than manuals !

The "CR" porting in the cylinder would require a larger tapered shorter pipe transfer. Over the smoother longer tapered pipe. This would soften up the hit between the two. The diameter of the pipe helps the exhaust leave sooner which sucks the new gas from the transfer ports into the cylinder. At the same time the new gas in the crankcase in under pressure when the piston moves down. It super charges the transfer ports. Well in a way kind of.

I'm going to jump out on a Limb here and say that there is a difference between a 83 CR and a 84 WR AC Cylinder besides the part Number. I'm going to say that the 84 WR uses the 83 WR Exhaust Port. Mine is measuring about 44-45 MM width or the same or less than the above Service bulletin for porting modifications. So if You start out with a 84 AC Cylinder, there is no need to change the Liner to a 83 WR make the above Modifications. However I do not have an 83 CR Cylinder - Liner to measure the Width of the Exhaust Port, I am assuming it is wider than the 46 mm in the Bulletin , hence the reason for replacing the Liner. If anybody has an 83 CR handy they could measure, please chime in.