2008 2.9 Thought I had carb issuse but have swaped carbs of same brand and size, what is happening is it revs fine 1st thru 3rd but in 4th and 5th under a load the thing just falls on its face like its run out of fuel or has lost spark. I can pull clutch in and it will rev fine with no load. It does this from 1/4 to W/O
any idea what the problem is? 118 main 38 pilot