I have the same carb that had the same problem.I tried most of the things mentioned so far.Also tried 50 cc pumps.If anything it got worse.I took the mettering blocks off,driled the pre set emulsion bleed holes(8 holes each block)to .033 then put idle feed restricker jets in all the holes. .031-.031-.028-.028 top to bottom.60 ft time went from 1.5s to 1.3s.You should see the rubber on my garage floor,when I was done I could pick the wheels up before sliding out the door.Might be something to think about if the other things mentioned don't fix it.Bill.