First of I want to say this is an awesome site! Been on it all morning.Here's the problem and I'll warn you this will be long. I was given 2 machines. One is a Yamaha excitor II(black & purple) and the other is a red machine that just says excitor. They are both 570's and I'm guessing early 90's.I put the engine from the Excitor II into the Red Excitor. I can getit to run for about 10 seconds before it starts popping out the left carb and dies. IT smells like exhast smoke after it pops. I have rebuilt the carbs,still does it. I have rebuilt the fuel pump,lines and filter,still pops.I have switched carbs from the other motor,still pops out the left carb. I have switched carbs from left to right,still pops.I have pulled the motor,pulled the flywheel,cleaned the magneto and still pops. I got desprite and pulled both cylinders of last night and they lok beautiful along with the carbs and pistons. I did notice alot of fluid in the bottem of the crank case. Oh yeah,I have also switched the coils with no change. Did a compression check and I have 125#'s even accross. What do you think of maybe the little cdi box being bad??It's about the only thing I havn't fooled with.PLEASE HELP!!