Ever since I was little we have always had a 150cc gy6 yerf dog go kart, and it was always the baddest one around no matter who came to race it. When I was little I helped my dad build that engine and after we got it we put some kind of mean atv carb on it, a connecting rod, and a cdi. There is more done to it but I can't remember, after we done everything to it that thing will crank 14k without a problem and makes about 13 hp and the clutches are tuned for racing. After 7 years of the reign of the big red, I came across a Yellow Jacket go kart with a 6.5 hp tecumseh with a bad carb. I rebuilt the comet 30 series and got a brand new 212cc predator and put it on my little go kart. At first my dad laughed so we took the karts out and drag raced them on about 100yds of field.... I got annihilated, badly, and he made fun of the stock, lean jetting and my kart adopted the name and is now called the "lean machine". I went inside after the race and started searching about my engine, needless to say I found an abundance of help, so I started the build with just the basic things like a new plug, racing air filter, .035" main jet, gx-140 e-tube, and an rlv header, however my dad had researched about my engine too and realized a problem might soon arise so he completely tuned up the big red and debaffled the exhaust, and re jetted the carb to make it meaner. The next race was a little better for me I didn't get destroyed as bad. I came inside after losing again and done some more research, this time I was dead set on becoming number 1, I ordered a billet rod and flywheel, a .040" main jet, removed the governor, a bored honda carb, a black mamba jr cam, 26lb valve springs, chromoly pushrods, a fuel pump, and some stainless valves, then I ported the head and checked gasket alignments on everything. After putting in some go fast parts into the lean machine I got the engine ready for round 3. We lined up the go karts out side and go ready to race, when the go flag was waved we both smashed it and both of the karts pulled the front tires about a foot off the ground, after my wheels touched the ground my kart ROCKETED and the big red was cranking hard and wasn't trailing by much, but it didn't have the guts to pass the lean machine and lost by about a car link. I finally claimed the number one spot and have destroyed any minibike or go kart that challenges me. I know alot of people who didn't believe that I beat the big red, they thought that 13hp and 14,000 rpms with the power to get it there, was a combo that was untouchable by an engine that was made to go on a log splitter. With hard work and dedication you can do anything with one of these little engines, they are tough too mine has lasted about a year of extreme abuse but as long as it has oil it runs.:thumbsup: