I've got a 2002 YZ426F with a Keihin 5JG6 500 Carb on it, that has a flat spot on low RPM acceleration. It started on my last ride. I ordered a Factory R&D P-38 for it figuring it would cure what was happening. When I pulled the Carb it appeared that the Pump wasnt working at all. Yes, the bowl was full and all the passagways were clear EXCEPT when I tried to Push some B-12 chemtool through the port in the body to the spraybar it appears clogged. My question is... Does there need to be venturi/manifold vaccum in order for this to work? I was under the impression the the pump was like an automotive type the will squirt as long as the bowls are full but i'm not sure about this one. Is there some type of valving in the lower part of the main body that doesnt show up on the factory exploded view of the carb? I noticed that the Lower part of the main body is removable (4 screws) between the float bowl and main body that has factory sealed screws and dont want to split if if I dont need to. On an added note is B-12 chemtool too hardcore to use on this type of carb? Thanks in advance to any replies/info anyone has.