Both bikes ran a 70 jet (a little fat) and speed carb with the MZ and a CNS bored to 16mm for the Bertha,Both ran well with stock gear and these engines have the ports and transfers corrected,and ment to flow well in the bottom end for prolonged use.They both have 168 exhaust duration,130 transfer,120 intake,and 19 degrees of blow down duration, stock cranks,cases,piston,intake,heads,cdi basicly just a cleaned and corrected engine not meant to scream.Admitedly the MZ 65 pipe showed a big improvement over any other pipe currently available by breathing well and cleaning out quickly,It staged around 6 grand and has a narrow band maybe 2000 rpm then falls off but keeps reving if let build up to it another 1000,by that time the stock crank was shaking like mad and had to let off it got up into the high thirty's so not bad, with stock gear it pulls well accelerating up grades no problem.The Bertha didn't like being fat you can here it the bike with camera has the Bertha on it and though it sluged its way up the side of mountain it never cleaned out,never staged,had a slight improvement over stock in the bottom end but not that great of acceleration,we'll have to see what happens when jetted properly.The Bertha ran at 285f at the top of run and the MZ 65 was 20 degrees cooler,I'm going to try them both on a modded engine (fully done) in their stock form then I'm going to cut the header off the Bertha and enlarge the dia of the first bend(90 degree )and flange and try a smaller stinger.The MZ pipe will have it's header shortened so that it stages higher up in rpm just to see what can be had from it.I know that this pipe will suport 8hp at 9 grand after that I'm curious to see for myself in the real world what it will do!
Here are a few videos. The one with the stock kit muffler silencer (which is louder than the fiberglass packed silencer) is modified, inside drilled and a larger exit stinger on the end. Also that exhaust pipe is modified at the mounting part to the engine, slip on with springs and a little larger inlet.
To me they are a nice loud, not crazy loud. I never ran it without a silencer so don't know how loud that would be, but imagine it would be very loud.