Marlowe I am just starting work on a homie 25
And i am looking to go wild on it as its going in a hovercraft which is not following any other design than my own
I am looking to get an ignition for the engine if you can help me out with an ignition i will post results etc up here and maybe we can all learn something regarding the curves
i have a crude form of dyno in my test equipment that measure time between a certain rpm to a time between another rpm of which i can set the start and finish rpm, also i will be using egt measurement so you know its going to be right.

I will be using a tuned pipe on this engine so i am not sure how that will effect the people that don't use one.

the reason they retard the timing up top is because the hotter a pipe the faster the sonic wave travels
as the rpm comes up a engine need a faster return on the pulse to keep it scavenging effectively
With the retarded timing the exhaust heats up and makes for a quicker return on sonic wave helping the engine to rev on
However when it get to the point that the pipe will no longer return the wave back fast enough we shove some timing back into the engine to help pick up a wee bit more power
putting the timing back in is worth about 200rpm (1.5 mile an hour where i come from)
Retarding it top to heat the pipe up is worth massive gains and no body would consider not doing it.
Here is my hovercraft it has had some beatings in its life the poor thing.
I made the mistake of putting the rudders to far away from the propeller but hey it was a home designed model