I picked up a 1972 CT2 175 barn find a month ago. It had spark so I had hope. I pulled the carb (314-E1) and gave it a good cleaning. When I put the carb back together I noticed that the slide was very tight and would not move up and down freely inside the carb body. I took it apart again and carefully inspected both the slide and the carb for any damage or deformities and found none.

The slide (Mikuni 2.0) looks brand new (like it has never seen the light of day). I was told that this bike sat in the sun (in Mexico) for 20 plus years. Could it be that someone already tried to fix this carb by installling a brand new slide, only to find that it still sticks in the carb? I don't know the history of this bike so I don't know if someone purchased an NOS replacement slide or a new Mikuni VM slide (or if they even replaced it at all). Would the O.D. of an NOS slide and a new slide be different?

try to loosen the screwed on top cap, it should only be hand tight or it binds sometimes.

I believe that’s a flange-mount carburetor. If the nuts, or bolts, holding the flange to the cylinder are over-tightened it could warp the body. I’ve had this happen with old flange-mount Amal carburetors. Loosen both nuts, or bolts, and see if it helps.

Being that it's a reed valve bike - both ends of the carburetor are round, so it fits into a boot up front "ruling out over tightening the bolts on a early CT1 where the slide binds."

I spray a little bit of WD-40 inside the slide area and on the slide to make sure that it moves properly. There shouldn't be any bind. As far as the top cap goes sometimes they are tight and you need to wrap a rag around the top cap and gently use some channel locks to remove the after you spray those threads with WD-40 as well.

Some trivia.... Mikuni is a copy of the Amal.

Yamaha used bolt flange carbs on many reed valve models... through at least 1975 on some Enduro models...

Most didn't get spigot mounts until 1974...

And yes, overtightening the flange can warp the carb and cause the slide to stick. Usually the flange is no longer flat if that happens.

Is it an original Mikuni slide? Their logo is a small square in the corner of a larger square and I would expect to see it stamped alongside the "size" (eg 2.0, 2.5).

Just throwing this out there because it worked .
I had a bolt on carb that the slide would only move with considerable force. Almost had to pry it out of there. The barrel on end of cable at twist grip was even pulled off so someone had tried hard to move it.
Sanding inside of carb where slide was pinched cured it. Fine sandpaper wet with WD40 and crept up on it. Magic marker on slide will show where it’s dragging

When the carb is off the bike, top off and it still sticks.

This is a flange mount, reed valve bike. Unfortunately, applying WD40 does not help.

The flange appears to be flat when a straight edge is placed on it.