I installed a Uni clamp on filter on my ATC, before I rebuilt it it had the stock airbox with a K&N and a drilled lid. My bike isn't running right, so I went and bought the next two sizes up for my main jet. I am storing my bike in a buddies shop and his dad says I should have gotten smaller jets, because clamp on filters reduce airflow. I have always been told by numerous resources that a clamp on increases airflow and told him that, and he says it also increases turbulence at the venturi of the carb and doesn't allow as much air in as a airbox set-up because the box to carb boot acts like a velocity stack and reduces turbulence, thus letting more air into the carb and in turn the engine. Now I'm all lost on this subject and want some clarification, which is why I'm asking you guys. Whos right, me or the old-timer?

 

A clamp on filter does let more air in as for more turbulence????

 

My guess is that you will now be lean and you need to jet up. Why not try the choke test? Just fire up and get up to full operating temp. Then turn on choke. If it runs better then you are right. If it runs worse the oldtimer is right.