Honing 1974 Yamaha RD200

[Ocean1]

Does this sound reasonable?

No. Sounds like you're measuring the bore above the point the ring sweeps, it'll usually be completely unworn there.

A proper bore survey measures X and Y axis at the piston mid-skirt position BDC, Mid-stroke and TDC. No one of those should exceed the overall bore tolerance and no two should exceed the out-of-round or taper tolerances. Nore should the lip at the top be more than, say 0.05mm. You need either telescopic guages or an internal micrometer to measure it correctly.

If the bore survey does find it's oval by 0.1 then you need to bore it, and that means buying first oversize pistons, (if they're currently std). Do that first, give the lot to the shop with any factory tolerances or other data you have.

[Woodman]

You cannot measure bore wear even close to accurate with verniers.
A 2 stroke will have most of its wear in the middle of the bore where the ports are, making them reasonably difficult to measure accurately to see which oversize it will clean up at. The reason a 2 stroke bore is awkward to measure is that quite often it is hard to get a ball gauge or similar at a 180 degree axis because of the ports.