Isn't the PES designed to use with squared off lumps?? If that is the case then perhaps the high floor on the manifold and the tapered lump don't like each other at low r.p.m......just a thought .....if a/f was checked at a single point that could mask cyl to cyl distribution problems that are sometimes prevalent in a high rise....just food for thought guys; wish I could have been there.......fats

fats