accel pump question

What advantages would i have if i adjusted the accel pump screw without doing the BK mod,what happens if i turn it in or turn it out, im new to he game and im just trying to figure it out.............42pj-165mj-needle stock pos.-fs2 trns out...........

If you are talking about the adjusting screw right next to the slide pulley that comes with the Yamaha-only Flat CR, turning it changes when the pump begins to deliver fuel relative to the slide position. In, or clockwise, increases the delay and out decreases it.

So I guess you could call it the pump timing screw.

If you turn it in a half turn from stock you should notice a little lean/dead spot when you first crack the throttle. If you turned it as much as a quarter turn out from stock the fuel stream would probably hit the slide momentarily, resulting in a few drops of un-atomized fuel added to the mix.

The reason this screw gets mentioned in conjunction with the BK mod is that it usually works better with an eighth or quarter turn of additional delay on the timing screw.

If you start foolin' with it and forget where it was, there should be a dab of green paint on the screw head and spring that need to line up. Barring that, with the carb off, or with the sub frame and air box off but carb still installed, adjust the screw so that the stream from the pump jet just clears the slide as it goes up.

Hope this helps.


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