I replaced fuel lines and got the high jet adjusted so it runs well w/out bogging. The low adjustment has no affect. Has never idled well from brand new. I can see that the throttle plate looks completely closed on idle. I know there is a Phillips head screw below the high and low mixture adjustments. I would think that the throttle plate should be cracked open a bit. If throttle plate is to be cracked open, how much? whats the procedure for it's adjustment.