Drilling the muffler+Air Cover Mods
- Thread starter AaronF
- Start date
The limits/sizes are set by how much noise you want to add, and your ability to read the spark plug and adjust your carb accordingly.
Then you may gain a 1/10 hp or so.
Then you may gain a 1/10 hp or so.
Some pipes don't get anything from drilling just the end cap! You must look inside the pipe to see how you can make it flow better. (& don't go crazy with drilling too many holes! You don't want it too loud!!!) 
Depending on your pipe, if you can take the end cap off you should be able to see about three or four swirled fines running along the shaft inside your pipe. Cut those suckers out and put the cap back on. Try it like that first. You can drill two 1/8" holes on the end cap and noise level will pretty much be the same- but the end result will give you some pep if not mph. I've done it to all my MBs {7} and I'm a firm believer. Although now I just roll with expansion {adjustible} chambers on my bikes {better performance} all around.
Mine came with a black cap muffler(the one that just the bottom cap comes off).
I took off the end cap and drilled the 2 smaller holes larger and also drilled another 3rd hole next to the 2 small ones, then i put cap back on. Works good but also a little more noise. For the aircleaner housing just a couple of extra holes will be fine(dont make them on the top of aircleaner or water might get in).
I took off the end cap and drilled the 2 smaller holes larger and also drilled another 3rd hole next to the 2 small ones, then i put cap back on. Works good but also a little more noise. For the aircleaner housing just a couple of extra holes will be fine(dont make them on the top of aircleaner or water might get in).
I drilled three small holes in the muffler cap and didn't notice any difference or noise.I also drilled four holes in the air cover with no difference made.Thanks Joe,I learned from the last time to check the plug lol! Should I drill a few more to see what 'performance' I can gain? The flute deal?? (I forgot the name of it) is welded on the inside of the muffler and I don't have a welder so that's a no go.Thanks for all of your replies.
There are some pipes that you must drill through the baffles to make it flow better. (just drilling the cap might not do anything)
My muffler has a bolt in the middle of the end cap, but even after I unscrewed it. It could not be removed. The maximum inside diameter of the tail pipe should be 16mm. This is according to the size of the exhaust port. Stock tailpipe only measures 8mm. So, I drilled a second hole 10mm, and inserted a male brass 3/4 in. coupling. But I rebore the coupling to have a 8mm inner diameter. I used some muffler glue to keep it in place. It now has a dual tail pipe. Torque has improved a lot, four stroking is minimized. However, you'll have to adjust the needle settings on your carb to run richer, because this mod causes your engine to run leaner. It now has an aggresive sound but not that really loud.
