Noisey exhaust

2 stroke of luck

New Member
Dec 29, 2008
Hobart Australia
I have a ZBOX 2 stroke 50 CC engine mounted to an old mountain bike.
The motor is still running in (done maybe 30 km).
I would like to make the whole engine more quiet, especially the exhaust, since I rely on hearing cars coming from behind as a safety issue.
I have read that you can put extender tubes on the exhaust to make them more quiet, but does this decrease power and increase back pressure ?
Any comments welcomed!


Master Bike Builder & Forum Sponsor
Dec 28, 2007
Duvall, WA PNW
No doubt the engines are noisy. The clutch gears are loud. Get a cover. Just combustion explosion noise....not much you can do except try fin inserts.

The main thing you can attack as you say is the exhaust!

The best combo for me is an expansion chamber, standard silencer and a muffler (see pic). It's marginally quieter than stock at WFO. It's way quieter at idle to 1/2 throttle. Plus more power than stock, easy..mbv.


Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
up north now
An extension will rapidly decrease power and rpm, and increase heat the longer you make it, and they don't seem to cut the noise much. I have tried one up to 18" long and it was not what I thought it would be. In fact, I am removing it.

You can glue a mouse pad on the right side cover and as pablo suggested insert some rubber pieces between the fins....both will net you a much quieter engine.

2 stroke of luck

New Member
Dec 29, 2008
Hobart Australia
I have added the "fin inserts" and glued a neoprene mouse pad to the clutch cover.
The noise is noticably quieter now.
The mouse pad looks good because it has a picture of a tasmanian devil on it.
I took the bike for its first real trip and it went really well except for the vibration through the handle bars, but I can put up with that.
I found setting the idle speed so that the engine cutout with no throttle was quite handy going down hill and coming to a stop.
I will start to mix it with the traffic soon, now I have the riding techniques better worked out.