also after the Kulana expansion pipe mod, I had one of the short expansion pipes I had ordered from Dax when I bought my last GenIV lower, the port flange as normal had horrible matching to chamber and to engine port which is a huge power robber on these engines, I took my pneumatic die grinder and did some nice widening and smoothing of the flange so that it is as close to port matched as can be had with a rectangle engine port going out to a round port flange which is now rectangle as well and then has a nice bevel tapper into th chamber tube.
After getting this port matching done, I mounted it on my oldest and first Mountain bike build that has been running strong since 2009, got the old 66cc BGF Red Bat engine, this little engine is by far the quietest non rattling china girl I have heard, doesnt have all the clutch side rattle and clanky sound that all of the china girls I've owned or heard always seem to have, it has zero mods done to it with over 2000miles, it aint no speed demon but with the 32T rear on the 24" rear wheel it will cruise at 28-30mph all day and never miss a beat, it is so dang quiet with this pipe it blows my mind, I figured it would be loud and high pitched but it isn't at all, been raining all day yesterday here and all the dirt roads here are pretty muddy but hey.... that wont stop a country boy from going on a ride so after it was almost completely dark I headed out down the wet muddy road and did about a 2 1/2 mile ride..... little engine just ginning right along real nice, made it back to the house with mud on my front...... mud on my back........ but a smile on my face........!
Heres a pic of the old girl with her new hookerbill nose pipe....LOL!
Oh and Yeah I know I Know...... the chain is very loose, gotta get that tightened asap, but actually I have road several miles with this chain loose like this and because it is perfectly in align it has never tried to jump off...LOL
I dont recommend doing it though and I wont be riding this one again until the chain has been adjusted.