I have the very same problem with my fuji 50ei. I had to get a new spacer & gaskets as the old spacer was cracked from the carb mounting bolts being too long. I too, put spacers under the heads rather than cutting the bolts down. Since the engine wasn't accelerating past about 3000 I did all this plus rebuild the carb (the diaphram seamed a bit dry). I've got it going to about 4000 or so but no further. Past that point & it stops cold as if it ran out of fuel or had the switch flipped. I didn't do any honing & this engine was in a nose in crash. Yea, I checked the runout on the crank & it's OK. If I open both needles up a lot it will go to full throtle but with little rpm & no power. I'm stumped! Can anyone help?--------joe