I stumbled on this forum while looking for tuning information on my IT400 Yamaha Drag Bike.
The engine is a bone stock IT400. I got the bike for $160 and it had less than 1000 km on it. It had been left oustide for years so the seat was rotten, the carb and petcock full of goo, and the plastic all faded. I fixed it up and it ran great as a trail bike ... gobs of low end torque. However, trail riding is not my thing and I always wanted to build a drag bike based on a two stroke dirt bike, because I had seen some at the strip over the years cracking off really good times.
So far I have only modified the engine by making my own expansion chamber from a snowmobile. It is not performing well as a drag bike. I am looking forward to lots of mods to up it's performance in the quarter mile.
It has only been to the track once. It kept starving out after the 1/8th mile. I had a tiny petcock and a tiny fuel filter. I have changed those since. I have been researching all kinds of two stroke tuning tips. I would like to find a top end from a 1976 YZ400 which had more high end. If I can't then I will likely get out the dremmel and started carving on the ports. I have a wad of jets to play with. Then there are reeds, squish shapes and tuning of the expansion chamber... and sprockets. I have 15/45 but I think I can get 18/40.
I'm looking forward to learning as I read through a zillion threads on this forum.
Peace & Grease, Dennis Smith
Prince George, British Columbia, Canada