I have a full Yoshi system as well. If your head pipe is purdle you are too lean. Needs to be golden brown. The pipe improves your power band giving you greater touque mostly low down and mid range. Your high end improvment is minimal, so dont expect it to be much faster top end. Every raptor I have ridden with another pipe backfires slightly when you let off the gas after heavy acceleration so dont worry about that.

 

Larger jets will not cause you to get poor gas milage. Incorrect jetting will. Just a thought!