Hi,
looked but can not find the stock front fork tube protrusion above the top triple triple clamp and the min and max dimensions... 78 yz250E..
thx, Joe

I'm not 100% sure on the YZ, but on many models of that era with forks that extended through the clamps, Yamaha scribed a line on the fork tubes that lines up with the top of the triple clamp.  

I can't recall ever seeing a "min/max" but there might be one?  I'll look and see if I have a Yamaha Competition Tuning Manual for a 78.  

Pretty sure they do have a scribed line to set flush with the top. But it's a bit of personal preference really. But don't go so far through that the wheel might hook the guard on full compression. Good model you have there, that & the 400 in 1978. I got the 400 new one "79, a one year long stroke motor & was my favorite looking back.

Thanks will check for machined rings like a lot of forks have...