Not sure on the pics you’re referring to but if 2.5 is the number yall think is best.  I will jot this down when mine all comes together.  The 3.4 came from the Yami Service Bulletin 235.. 

Cheers Guys.. 

drive.google.com/file/d/1hnZYm7FNdqyyZ3b...SZ/view?usp=drivesdk

Thanks for all the input. If the ports look right when I compare my original and the second set up I bought I will use them as much better condition

Still odd no capacity marked on the barrel/jug

Thanks all

Ian

Not sure what they were smoking in that service bulletin @3.4, but I want some to try lol. 250's are 3.2 with shorter stroke.

Hmm. Thought I had sent this reply once. Seems not.

So removed head and barrel last night. Barrel well and truly stuck on studs. Lots of penetrating spray down the holes and lots of wiggling with gentle persuasion saw it come off.

Heads are exactly the same. Good

Barrel ports exactly the same. Also good.

Differences are my existing barrel has machining of the fins for a decompressor but has a blanking plug and not sure it is fully “finished” for fitting one?
My replacement does not have this machining and is solid fins. So the replacement would seem to be an earlier barrel. Also good for my 1970 bike.

The existing barrel has the CC cast in it and the earlier replacement barrel is blank All considered not sure what that means, if anything.

Existing piston crown is stamped 96?

New pictures attached to show these points.

Replacement parts will be put back on after a good clean of all faces and the rusty studs.

Thanks for all input on this. Appreciate your time.

Ian

New photos attached link. share.icloud.com/photos/050TGtjs2C5pswO0_W_aQtdwg