Posting this up for a mate in the US who has just done a partial restore on a 907. He's having gearbox issues and I was wondering if anybody might have a clue as to what the likely issue is If it's shifted into third or higher it will not shift back down into first, unless the bike is shut down and then run up and down by hand. If that's done then it will shift back into first. I realize its not much to go on and I'll try to get more info. Even if somebody posts and gets me to ask specific questions that may narrow the problem its appreciated John
It sounds like a selector drum/fork issue? I would pull the l/h case off and check the shifter mech first.
I tried to find an actual Paso exploded view but they are all similar. If spring item 10 becomes broken the gearchange operation will be 99% unaffected surprisingly but if the 'hook' on the pawl item 14 becomes worn or bent due to someone being heavy handed coming down the gears (fairly common for the downchange hook) and especially if combined with the above broken spring, then coming down the box through the gears becomes temperamental at first and eventually almost impossible whereas changing up the box operation will continue as usual. It's also quite common for spring item 17 to fracture which can give similar symptoms but with an added symptom that gearchange lever will become 'floppy' not returning to the 'middle' position on up and/or down change operation.
