[Ultimate Converter Concepts]

Could be a few different things including carb(very importanty) or a sprag problem or stator selection thing. If the converter is too tight it will pull the engine below it's peak torque and it will labor untill it gets back to peak and then take off, it will also be noticeable on the gear change, pulling the motor down below peak tq. Is this a "glide or a three speed set up? How high do you turn the engine? Do you have any dyno number's on the engine? Looking for peak tq. and how much.