I find the Tanak PF-4000 ear shattering loud !
I was shocked after finishing my kit built today. Threes no way I can use this motor. I have a tandem bike and my wife sits nearer to the motor. She'd have to wear ear plugs absolutely. I don't think I'll use this engine again. I'll have to see if I can switch. I'm not going down that road where I would try to string a big modified exhaust on the bike. I like the compactness of those standard box type mufflers.
The prior kit engine I had on the bike was a smaller engine so I guess it figures less sound but Wow I can't believe anyone would use a kit with a stock engine like mine in any populated area.