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Looking at buying a 70cc big bore kit for my 2009 Yamaha yw50. I am on an extreme budget & cannot afford both a BBK & a performance exhaust. Is there any modifications I can do to the stock exhaust to make it perform better & help me get more power out of a BBK?
 

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Hello Moore_77363,

I had installed a Malossi cast iron big bore kit on my old 2003 Zuma/BWS and kept the exhaust stock. I knew it wasn’t a super fast racing BBK but I got more torque and and a few MPH faster. At least pegged at the maximum on my speedometer. I guess that you could start out with a BBK and maybe later invest in a pipe. Best of luck. 🛵💨
 

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If this isn't already OBE, you can try polishing and enlarging the stock pipe where it meets up with the engine. I used a dremel grinding stone marble, white and about 3/8 diameter to reach in as far as possible, just over an inch and made that as smooth as possible as I'd noticed carbon buildup when I removed the pipe, then working towards the flange I enlarged the opening only about 1mm. This is for a horizontal Minarelli engine. I also installed a new kevlar belt and added a 1 1/4 inch high rpm (32,000) mini cooling fan to the air intake box on the back, thinking it'd add boost. I cored a hole in the airbox back and covered that with window screen and mounted the fan such that its housing blocked off the original rubber air intake. Well with the fan running it acted like a kill switch at all RPMs, but with it powered off that bike was quick. I am getting 0-30 in about 8 seconds and 0-40 in about 13 seconds and 40+ at 20 seconds. Oddly enough when doing cleanup I removed that fan thinking it unnecessary but the bike had terrible flat spots in the performance so put the fan back in. I have no idea why it works so well but am sure the fan impeller spins while the engine runs at higher RPMs. The fan I used is about an inch tall and designed for cooling 1U rack units.
 

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Nothing to see, really. Exterior looks stock and since I ride daily can't show the inside of the pipe but it'd look almost stock as well. You also might want to look at youtube videos on porting and polishing heads. If you're careful and patient, smoothing the exhaust port and enlarging the intake can do wonders. Also, depending on the year of your zuma check for a throttle restrictor on the carb or throttle body. And if fuel injected but running slow, consider ultrasonically cleaning the injector in gumout type solvent.
 
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