just installed a 80cc big bore kit and want more speed

[Dodgeme]

Originally Posted by blueboy5000

Having installed literally dozens of bbks on 139, 1p40, 157 and 152 engines, as well as being extensively familiar with all makes of scooters since I built my first Lambretta in 1988, I will now state that achievement of any flat land speed of over 5Omph on a 73cc 139, is pretty good, and about all it will do.

Mods help the 139 gain acceleration, but really don't do anything to the top end. A 73cc engine is approximately 4cid, or 1/3 the displacement of the cheapest lawnmower available at Wal-mart.

To assert the modified 139 is capable of speeds in excess of 55 mph on flat ground, is untrue, and unrealistic.

unfortunately I have to disagree because mine did 50mph clocked by gps, chase cars, and a police radar gun going up a 4% grade and that was only at a 47mm bore with only a 1500 rpm gearbox side cvt spring upgrade, but without improving the cylinder heads flow characteristics, without improving the lean factory a/f ratio (stock carb), without regearing, without a full synthetic motor oil, and without retuning the engine side of the cvt. Now if you had ever tried increasing the engines pumping efficiency you would find that indeed you are wrong and that you really need to learn how to correctly optimize an engine. I trained in college and yes I have a degree in auto, diesel, and industrial applications including high performance and how to maximize any engines overall performance and longevity.