kiln Posted October 28, 2011 Posted October 28, 2011 I sure hope that everyone can voice their opinions about the topic at hand. My setup is as follows: Gearbox standard, front sprocket =15t and rear sprocket=47t. New carb with standard jetting and K&N air filter. Boyesens reeds. New OEM piston & rings. BR8EIX spark plug. Standard exhaust & tailpipe. The bike starts fine and rides with a lot of torque in lower gears. But when riding up to 5th gear, the revs pick up nicely and goes 8000+, yet when changing to 6th gear, the revs drop to 4500 with WOT and speed drops progressively as well. When in top gear going at WOT there seems to be a willingness to go faster but it feels like brakes is applied, going at 3/4 throttle a feeling of just cruising is at hand but there is no desire from the engine to go faster. Do I open the bottom end for a bearing replacement exercise or would you recommend that I change the front sprocket to 14t or the back to 49t? Any suggestions welcome and if possible I will try to test them in the coming weeks and keep the post updated.
kiln Posted November 6, 2011 Author Posted November 6, 2011 Oldgit can you, Neo or cynic Comment please.
Moderator Airhead Posted November 6, 2011 Moderator Posted November 6, 2011 remind us kiln... standard carb jetting and airbox? How did it start to do this, how long ago, anything changed at that point???
kiln Posted November 7, 2011 Author Posted November 7, 2011 Standard carb jetting, and standard airbox with k&n filter. It started this issue after installing standard yamaha piston and rings, checked and verifeid gudgeon pin sizes from skirt etc.
Moderator Airhead Posted November 7, 2011 Moderator Posted November 7, 2011 Standard carb jetting, and standard airbox with k&n filter. It started this issue after installing standard yamaha piston and rings, checked and verifeid gudgeon pin sizes from skirt etc. standard yamaha? I thought you had fitted wiseco with a different cutaway for the intake
kiln Posted November 7, 2011 Author Posted November 7, 2011 Yes, I had that wiseco piston in as a temp solution whilst waiting for the yam piston, a time investment worth waiting for. After much deliberation/testing, it is my belief that standard is best. Also running premix with mineral oil. Only the sprockets to fine tune.
Moderator Airhead Posted November 7, 2011 Moderator Posted November 7, 2011 Yes, I had that wiseco piston in as a temp solution whilst waiting for the yam piston, a time investment worth waiting for. After much deliberation/testing, it is my belief that standard is best. Also running premix with mineral oil. Only the sprockets to fine tune. Ahh I thought you had problems with the wiseco, so you fitted a yamaha piston and you still have problems with power output? why would gearing down solve the problem? surely the bike will just be slower
kiln Posted November 8, 2011 Author Posted November 8, 2011 I have a 13t in front and 47t in the back.The bike gets nice and quick to 6th gear but at 9000+ revs the engine wont last. so i will try 14t in front and see if any improvement is to be made.I had 16t in front which is why it dropped speed in 6th.
Moderator Airhead Posted November 8, 2011 Moderator Posted November 8, 2011 I have a 13t in front and 47t in the back.The bike gets nice and quick to 6th gear but at 9000+ revs the engine wont last. so i will try 14t in front and see if any improvement is to be made.I had 16t in front which is why it dropped speed in 6th. so theres nothing wrong then, but you are concerned about prolonged high revving of the old girl? If thats the case I would just fit whatever was the standard...I think that was 15T on my 175
Moderator Cynic Posted November 10, 2011 Moderator Posted November 10, 2011 Hmm, 16/49 is the stock ratio but 15/47 is close enough to stock if thats what your after. That 13t sprocket is effectively a 20%drop in gearing, no wonder she reved her spots off.
kiln Posted November 17, 2011 Author Posted November 17, 2011 I used a 14/47 setup and she purrs happily at 7500rpm in 6th gear, retaining all her spots....I seem to have found the bike's the G...sweet spot.
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