Some warning signs were there...
Figured I'd raise the gearing slightly for more relaxed cruising and possibly another 5 miles per tank. Also, figured going up one tooth on the rear at the same time would also keep her peppy enough.
So checked on the site, but couldn't see anyone trying this sprocket arrangement on their 900.
Ordered sprockets from ebay - plenty selling a 43t rear, but couldn't see anyone doing a 17t front sprocket for the 900. Widened my search to the 850 and there were several to choose from, so I ordered one.
Stripped all the cover gubbins away from the front sprocket and whipped the 16t off. Placed the new sprocket into the chain run, but when I tried to put it into position there was a thick plastic guide which fouled the chain no matter what angle i attacked from. Took the guide off an introduced it to an angle grinder to shave a few mms off it.
Attempted to refit 17t sprocket but despite tapping with a rubber hammer it wouldn't go all the way on. Took it off and compared it to the existing 16t sprocket I'd taken off. Discovered that the dimensions of the inner holes varied - the ID of the 900 sprocket was about 2mm wider than the 850 version! This surprised me as where they can, Yamaha usually re-fit the same parts. Guess they wanted a stronger gearbox output shaft for the 900?
Anyway, not a complete waste - I flipped over the 16t sprocket (to use the unworn sides of the teeth) and fitted the 43t rear sprocket. Have now gone in the opposite direction, with slightly more acceleration than standard (but sadly speedo will be even more inaccurate). Considering whether to try another gearing arrangement - 39t rear sprocket with the standard 16t front, or leave as is.
So, there seems to be plenty of ways to increase acceleration, but far fewer 'cruising' options...
