The seller wrote:
The motor has the spacer under the Cly. So you can use a 79 YZ Top End..(Easy to find parts
which to me could either mean that it
has the F model barrel or that you
could fit it if you wanted. Now I've thought about it a bit more I realise that the '79 model barrel wouldn't fit without a fair bit of surgery so I think he's used the late rod, piston and skirt. The 214 to 311 rod and appropriate piston change isn't an issue, I've done it myself in the past. The issue now would be in using the F model sleeve and porting the original YZ barrel to suit which would in effect give you '79 model porting. If those porting specs can be achieved by conventionally porting the YZA barrel then I reckon he's legal but if there is a major re design needed to bring the YZA up to F specs I have a real problem with it. Not being familiar with the YZ250 F I'll leave that dilemma to my more learned Yamaha aficionados. I'm curious to know whether the F model porting specs are achievable in an A model barrel.
Id like to see that engine on a dyno compared with a un modifided one.i take it i has a different stroke ie haveing the spacer etc
As Johnny O said, changing the rod length has nothing to do with changing the stroke. The stroke is changed by altering the distance between the crank centre line and the crank pin centre line. It's a common misconception that changing the rod length changes the stroke.
Looking at the engine in the bike it's fairly clear that he's using the original YZA barrel so if the liner change is kosher, I reckon the bikes kosher*. The wording of his ad could be taken both ways.
*
I still have issues with the swingarm though.