Sudden change in performance

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#1 Unread post by **scan** » Wed Nov 21, 2007 10:11 am

About a week ago I was riding my bike and there was this pop. It wasn't loud, but I noticed the power seemed to drop a bit. After that it seemed like the muffler was a bit louder and also I can hear the decel popping much more than before. It is able to respond as usual when in the upper RPM range and doesn't seem louder there, but when it is in the lower end of the RPM range (around 3000 or so) it seems to pull less than before and also sounds much louder. For reference my redline is 11000.

Anyway, I thought maybe I blew a bit of packing out of my Yoshimura slip-on and wondered if that could effect the performance if I lost some of my back-pressure? I also am overdue for my valve check, carb balance, and plug change, but I never thought much about my muffler. Can I repack it, or do you just replace the whole slip-on?

slimcolo · #2 Unread post by **slimcolo** » Thu Nov 22, 2007 5:52 am

Sounds like back pressure. (for sure if you lost some packing) This can be adjusted out, on most bikes, if you have an adjustable main jet.(but pipes will stay loud) Could also be carb sync.

Not sure about Yosh pipes but there are several makers of Silencer Repacking material, or you can go with one of the cheaper old skool fixes. (fiberglass insulation or steel wool) but will have to repack every week or so.

My advise would be to do your tune up before you attempt further work. (tuning factors often mock much greater problems) Your problem is most likely back pressure but could be caused by tuning, (valve adjustment, carb,etc) Vacume leaks,sticking float(carb),loss of/flucuating fuel pressure, dirty filter(air or gas) Timing may have slipped but is very unlikely, especially with electronic ign.(I guess this is part of tuning)

#3 Unread post by **scan** » Fri Nov 23, 2007 11:08 am

Thanks for the thoughts. I was planning on getting the other stuff done anyway, and it is overdue. I have the same plugs in that came with the bike new. I have a spare set, but I never needed them. I change the plugs, get the carb sync'd and check the valves then worry about the can.

BuzZz · #4 Unread post by **BuzZz** » Sat Nov 24, 2007 6:43 pm

I'd check your exhaust can first. Packing can and does blow out, but sometimes it doesn't make it all the way out, creating a blockage. This will affect topend power more than lower end power and affect the exhaust tone.

I have also seen the perforated inner tube beak up and obstruct the exhaust flow, with the same results.

If your can is bolted together, it's easy to get apart to re-pack and inspect. If it is riveted together, you just have to drill out the rivets then re-rivet it back together.