Set the needle at peak with the nose
pointed up. The prop will unload a
bit when it gets moving so it needs to
be a little rich.

You could try a 6x3 prop. It will unload
a little less than a 5x4, though you won't
have the top speed GLH implies.

If you aren't using a muffler, you can take out
the shims. They probably aren't causing the
problem, but they will decrease the power
when used without a muffler. Running
without them will give back some of the
power you lose by running a bit richer.

Finally, you can block the crankcase pressure.
I always found pressure to be finicky.
Running stock is the most reliable, though
not the most powerful. For competition, go
for all the mods on multiple engines to find
one that is great. For fun, stick to reliable
stock setup.

Jenny