No oil in Midvalve

I have a 03 YZ250 and changed the fork seals and when filling with oil I'm suppose to pump the rod up and down 10 times to pull oil into the midvalve chamber until the action is smooth. One fork works the other feels like it will not pull oil into the inner chamber. There is no hydraulic action only the feel of the spring. The base valve nut was loose, so I put lock tight on it and tightened it. This changed nothing. Is there an O ring or seal in the midvalve that is allowing air vs. oil to be pulled in?

put your hand over the top of the open fork leg and compress it hard , it forces the oil in

I'm not sure how compressing fork leg will push oil in. It gets pulled in when the fork leg is compressed with not spring and you pull the shaft up and down in a pumping action pulling oil in and displacing air

Has your suspension been revalved? I had a similar issue (fork leg had very little resistance when cycling) when I did my revalve. Somehow I assembled with the piston not locked together properly. I had to go back into the midvalve and fix it. If your base valve nut was loose it's possible that the mid-valve nut is loose too?

I'm not sure how compressing fork leg will push oil in. It gets pulled in when the fork leg is compressed with not spring and you pull the shaft up and down in a pumping action pulling oil in and displacing air
I's a bleeding procedure. I remember the valve in the bladder forks would make fits like this and the pressure trick would save alot of time. It goes much faster if you put your hand on top of the fork tube and compress, the variation in pressure helps ,you will hear the bubbles. Or, you can wait overnight and pray for the oil to find its way... It's a trick to make the same work faster.

make sure the base valve check plate is working properly.

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