If it's popping through the exhaust, wouldn't that mean a hydrocarbon backfire? The bike may be too lean, now that it's running less restricted, and needs more fuel. This would be a Main jet, and pilot screw adjustment. You have to do a Spark Plug reading and see how they look to determine if the bikeis too lean or too fat on it's mixture. I don't see the pilot jets affecting this much really, except at idle. Maybe someone else can chime in.?