11/18/2017 7:11 PM
Edited Date/Time: 11/18/2017 7:12 PM
Thanks for the replies everyone. You'll probably flame away, but this is what I ended up doing.
I found out that 5/32 is nearly identical to 4mm. And I happened to have a harbor freight drill bit in that size that I simply could not believe how well it fit into the guide. I could also feel the snag in the guide that I installed, but the drill bit passed through the other two intake guides. So a friend held the head, and I chucked the bit into my hand drill and gave it a spin. After checking with the gauge, the snag remained, so I hit it again, and again, and again with some oil. After a few passes, I was able to remove that snag about 80% and the intake valve is now much happier in that guide.
However, I still had a problem from before and after my awesome harbor freight drill bit clearancing, and that was the intake valve wasn't hitting the seat square. You could clearly see where it was hitting 1/4 of the seat first. So I grabbed an old intake valve and lapped it into the seat. I know this is something you usually do to match a valve to a seat, but I was trying to match the direction of the valve to the seat. After several passes with a hand drill hooked up to it, I was able to refinish the offending part of the seat and now my "good" valve sits nice and square in there. I installed the spring and shined a light in the intake port and it looks to be sealing as good, if not better than the other valves.
I know none of this is the right way to do this, but I'm trying to do this restoration (http://www.vitalmx.com/forums/Bike-Builds,46/2002-YZ250F-Restoration,1316154) on a budget and I don't need it to be perfect, I just need it to be good.
P.S. The Yamaha manual does say to ream, and it offers a Yamaha part number for said ream. But the manual also says to lap the valves into the seats, so I'm taking their instructions with a grain of salt.