I have always been blessed with a very logical mind and have accomplished everything from engineering - designing - fabricating and erecting a 400 foot tower for radio communications to totally building/constructing my own house and invented numerous items and fixtures. I decided to prima pipe my buddy 125. I noticed on several rides that @ 40 to 50 MPH the exhaust seemed to be creating a pinging sound in the muffler. This sounded like accessive back pressure. After I removed the stock pipe, I took inlet and outlet measurments of both pipes. The stock pipe had an inlet of .74" DIA. and and outlet of .65" Dia.. Figuring area square inches that is .43 Sq in inlet and .33 Sq in Outlet. As the exhaust is expanding it is further reduced by 24% more restriction, causing back pressure. Now the new prima pipe has a 1.10" inlet (220% increase over stock) and a 1.38" outlet (450% increase). This pipe has made a remarkable difference on my buddy and no more pinging in the exhaust @ 40 to 50 MPH. Acceleration at bottom end has increased but top end has only increased 3 - 4 MPH.
I also used nail polish to put a dot on the handlebar that I can easily see. Then I also put dots on the grip to line up with the other. These dots are at closed throttle, 25%, 50%, 75% and wide open. This gives me a visual as to the throttle position. In headwinds etc. I drive by my throttle and not by the speedometer. I have discovered that 25% gives me 40 MPH indicated and 50% gives me 55MPH indicated and still allows for 100 MPG. Being a pilot we were taught to fly 'on step' and I drive that way. To explain- It is more effecient and not hard to do. Just accelerate to 3 or 4 MPH faster than you want to ride, then slowly back of until you are going the speed you want and you will be riding on the efficient side of the fuel consumption curve.
