05 March 2011

hacking the muffler


My stock muffler had a rattle at certain RPMs, and it was annoying. Also, going for a higher flow should make it run a little better. Looking online, I found performance mufflers for as little as $150, and up to $300.The single most expensive upgrade item! I could get a stock muffler for $60, but just to get rid of rattle? I found some other people who had modified their stock muffler to make it much more flow-through, but they had a different stock muffler than me.
 Today I had an opportunity to spend a few hours in the garage tinkering, so I unbolted my muffler and whipped out my hacksaw to see what I could see. After carefully cutting all the way around, I was surprised to find more junk inside than I expected.
 This is the loose part that made it rattle I think. It's a little passage tube that just fell. There was a lot of crud inside the end here. Well, I want to open it up to get more flow, so time to rip out that end baffle!
 Getting it out was fun, it was welded in two spots. A quick cut with my dremmel and some smashing and vice-grip work gets it out. There is a wire mesh holding a fibrous mat against the shell. It's not very thick, so maybe it's sound deader or thermal insulation? I dont know, but I ripped it out! The mesh was breaking down in a few spots, so it could have contributed to the rattle.
 The pile of some of the junk I pulled out. Most of the wire mesh went straight to the garbage can. It would be my luck that the fibers are asbestos and now I'm going to die from it. In the end I got it all out.
 To get the mesh and fibers out I needed to smash up the final baffle. It's all good though, it gives more open flow! It appears that the exhaust comes from the header into this tuned (?) pipe that has a U in the end. I thought about cutting it open with my dremmel, but decided not to. I'm not interested in a loud sounding muffler, just better flowing.
 I used my 24V DC home made arc welder to weld the little tube that previously was inside to the cap as a new tip. I then re-attached the end cap to the muffler. It's not a very pretty job, but it works. I'm not terribly good at welding, and the metal is rather cheap. I blew through several times but managed to fill all but one of the larger holes. Not a bit deal since I want more air flow anyway right?

Finally I took a little video to capture the new sound. To me it sounds like the 250cc motorcycles we used when taking the Idaho STAR course. A bit louder than before, and I can feel much more air coming out the tip. I took it for a short ride and believe I get smoother acceleration with slightly more pull. I really need to re-jet the carb to get more fuel, then lighter weights in the variator for more power. Next month!

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