Wow I read a lot of mixed up and wrong information here,so first let me say I travel mostly between 500 -1130 ft elevation's and jetting is not really effected until 1500 ft and above, under that is the same as sea level! Now the op's 21mm carb with close to stock port's and a 95 jet is awful lean in the top and will fall off hard after pipe peak,carb tuning is done from the pilot jet up not just the main!This means that if the pilot then needle were set properly the main will be larger to suit the higher flow at higher rpm and still perform properly from idle up to wot.If changing the main jet is effecting the idle or mid range then it's not tuned properly because it shouldn't have any effect on the bottom at all! The whole point to these engines is that they are cheap as dirt compared to most and it's not hard to get major improvements from them without having to spend alot or even any money if you know what to do,yes speed's will vary from user to user depending on ability but knowledge is key to get the most from your engine so read everything you can ask question's of those whom know and make informed decision's before altering anything!The lowest exhaust duration I've ever seen in these engines and mind you that was 10 years ago was 154 degrees not 130 something the current cylinder's are closer to 160,and stock port timing is capable of making decent power by just adding width,2mm on each side is alot! Raising exhaust port height by 4mm is ridiculous since each mm added is over 4 degrees so 16 degrees added to the average 160 is now 176 and that requires alot more work done to the engine than just raising the port to work properly!Last setup is key to making good usable power through out the range I know I use this video a lot as reference to what can be done with these and that's because there still isn't many people able to get 50+ from a stock setup,so here's the proof it can be done!
