Vintage Dirt Bike Q & A

Hi guys,

I am after the exhaust port timing for the 1974 CR250M so that I can design an exhaust for my MT/CR hybrid.
I know this information is in the back of the (gen.) Honda Shop manuals but unfortunately I do not have one and we do not have one on this fantastic site yet.

I know that the port opens somewhere around 88deg BBDC and closes somewhere around 88deg ABDC but was hoping someone could look up the actual figure for me.

Many thanks in advance,

Grae.

Hi Guys, surely someone out there has got a Shop Manual for a '74 CR250M?
The exhaust timing values are listed in the Specification section of the manual.
I am trying to work out the tuned length for my MT/CR hybrid so I can make a single or perhaps twin stage expansion chamber for it.

I didn't really want to purchase a DTI to measure when the exhaust port opens and closes so I was hoping that someone would be able to help me out and look in their Shop Manual. Please?

Thanks in advance,

Grae.