I update my syncros to Carbon syncros from synchro tech and all gears are fine but 3rd gear keeps popping out for no reason I want to know what could be the problem it has new syncros.

 

It has been a while since I rebuilt a transmission but my ITR was popping out of 2nd gear and I replaced the applicable synchro hub assembly. That solved the problem.

 

Are you using a short shifter? Only other thing I can suggest is that the grabbing surface on the gear might be causing an issue.

 

There may be something wrong with your external shifter linkage.

 

everything is original just did the synchros I heard it could be the synchro spring.

 

Had the same problem once but with fifth gear and it turned out to be I had a fluid leak. Make sure there is sufficient amount of fluid in the trans. Only use Honda MTF. Sufficient amount of fluid creates enough pressure to keep the trans in gear.

 

The synchro springs keep pressure on the brass/carbon synchro ring. If The spring is flat it will not have enough pressure to keep it in gear. That would be my thought if they were not replaced when the carbon synchro's where installed.