Originally Posted by AaronF
What size of drill bit and how many holes would be acceptable drilling on the muffler end cap and carb air cover? I wanna gain what performance I can with these mods for free! Thanks.
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.