Hey, My son has an 84 lt50. It doesn't want to idle down with the choke on or off. I have the air screw set at 2-1/2. It has a K&N and the stock pre-mix system. I have checked the plug and it is good. It almost always starts on the fist pull too. Any info would be a great help!!
You may want to check with Hetrickracing.com on Suzuki hop-ups. One thing to remember though is that when going to an aftermarket pipe, you lose bottom-end for a ton of top-end. This will require tranny mods (variator, weights, springs,etc.) Rich Hetrick should be able to help you with these.