I had an O.S. .90 4-Stroke ( inverted ) that started acting
up like that. Stick with those plugs, nothing works better.
I set the idle screw, and it would sit there and idle great,
all darn day....but try to give throttle....that sucker would
die right out, and was drivin' me nuts. Tried different
plugs, fuel, ect....nothing helped.
Here's what I found....the screws on the carb, and intake
manifold had begun to loosen ( new motor ), and it had
developed a small air leak. I had opened (and richened)
the low-end screw to compensate, and had great idle.
But it was TOO RICH to transition up off idle, and the
engine would die.
The 4-strokes are fussier about needle settings. The
2-stroke will usually run sloppy rich, no matter what.
When the motor kept "bogging out" and dieing out
coming off idle...I figured it was too lean....( like a
2-stroke ) and kept richening it up. It made it worse.
So the bottom line was....If it idles ok, but wont take
throttle...you might have to lean out the idle screw.
Hope this helps. If you have a long distance from the
pits to the flight-line...most guys use an on-board
glow system to avoid the dreaded "flame-out".
