ot,but 2 stroke related...pw80 bike exhaust..

[paz]

i know its off topic,,but as far as two stroke goes,,i dont think there would be a better place to ask...
i have been fooling with my young blokes yammy pw80...before hand it was a complete dog,,blowing heaps of smoke,,very limited in rpms,,and just pretty much powerless....what i have done is remove the auto oiler set-up...now running 40-1 premix,,was pumping in way to much oil and no way of adjusting...i also pulled the complete pipe off it,,found it was pretty badly carboned up,,,once all that was gone i found a restrictor right near the port(gonnnne)......now with all this done it is a totally different bike,,,,heaps more mid range,,,even breaks traction(slightly) with my fat ass on it....but what i want to know is ......from the power pipe to the stinger/muffler there is a pipe of about 3/8" or a tiny bit bigger...now the exhaust port is of about 1"....would this be the same as a saw and i should use the 80% rule and open up the little pipe to say around 3/4"????i know its not a race bike or anything,,,but do think it has a little more potential....

 

[MacDaddy]

no dont open it that much maybe about 1/2 inside dia and see how it runs

 

[paz]

i guess it is easier to go bigger later if i want to....shall give it a go at 1/2 id pipe...

 

[TimberMcPherson]

be careful not to kill the bottom end, with a centrifical clutch it can hurt its ability to get up and move.

 

[MickJ]

Yea you could play with the pipe size, but before you did that i'd be making sure the airbox/filter has as little restriction as possible and then re-jet the carb to suit the changes, seeing as you removed the restrictor it should be flowing a bit more air so might be running lean, different jetting, needle, clip position could unleash more power still.
The restriction at the back of the expansion chamber is there to re-direct exhaust waves back toward the exhaust port, which should be closed when they hit it, then they'll go back away from the port which is just opening, creating a vacuum behind and drawing out spent gas and fuel/air into the cylinder.

So i guess you'd either get more power due to extra flow (you'd need to re-jet to suit)
Or you'd alter where the power was delivered - ive got no idea which way it would be altered
For what its worth my KTM 300 pipe between the chamber and silencer is roughly an inch diameter (at a guess) and it makes around 50hp at the wheel...

Let us know what happens i'd be interested to hear about it!

Mick

 

[paz]

well i ended up leaving the pipe as it was.....turned out in the carby was where all the problems were...i lowered the needle(leaned it i guess) two positions...made a huggge difference,,,now rev's out to what i think it could and the young bloke has a smile on his face a mile wide......thanks for your input guys.....
btw....i also own a road rego'd cr500......???? i love my 2 strokes.....