Pilot manifold modified to flow! by hoser..Here is a 39mm PWK mounted to a stock Pilot manifold, if you look close inside you can see the match to the carb is not all that great but about normal for a production part, it is about as bad when a stock carb is installed, right now the 39mm opening is reduced to about a 37mm opening, the lip that needs removed will reduce flow and create turbulence, removing it or matching the mating surfaces to the carb will increase flow and increase throttle response. Looking from the other end, the cross section of the stock Pilot manifold is actually too large when using even the 39mm carb I would like to find a rubber substance that will bond to the stock manifold and resist fuels and oils so I could reduce its size and increase the velocity from the air filter to the crankcase. If you lay the stuffer on the manifold like in the picture below you can see more problems with the matching of stock parts, flow corrections are made here also by marking the parts with a marker then using a dremel tool and a carbide bit at slow speeds the material is removed slowly until the parts match this will remove the turbulence problems associated with stock parts. The manifold offset is another draw back of the stock manifold but is needed so the carb will clear the belt guard mount on the transmission, if I were building a all out race engine I would cut off the mount on the transmission so a straight manifold could be installed then fabricate a new mount for the belt guard.