HEI's either work or they don't- - - -it's very unusual for one to hit a certain RPM and crap out. An original HEI will start to spark scatter and miss at 5500-6000, but not below- - - -not sure about a rice-burner clone. Find the restriction in the fuel system- - - -filter, sock strainer in the tank, weak fuel pump, etc.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!