they where made by PC/RC "EFI-801" they work on jump switchs to set the proformance of the motor from the exhaust temp taken from inside the pipe near the exhaust port.
they also had the ability to set how the startup was from rich to lean... all you had to do was set the LSN so there was fuel spitting out of the exhaust and wind the HSN all the way out so the regulator would do the rest.....
they dont make them for the small engines but you can still get them for the large scale engines....
if they still allowed them ever man and dog would drive a nitro car.
my time using one you can get old motor that have lost there edge to go hard again for a while.
while the dollar is good i should send mine back to get fixed.