Changing the length of the push rod changes WHEN the spark happens. Changing the points on the bell crank change HOW MUCH total timing curve there is.
For the creative you can set up the linkage so the bell crank ALMOST goes over center, then you can get the timing curve to come in faster at a lower RPM. OR is you really want to be creative use another servo slaved to the throttle to run the timing..... get any curve you want that way.
ORIGINAL: Rcpilet
I've never understood what was meant by "tuning" the mechanical advance system.
Sure--you can advance the timing in the middle of the RPM range by adjusting the rod length.
But, then you've screwed up the timing at all the other spots in the curve.[
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For example:
Your idleing at 6* BTDC and your at max advance--or 28*--at 5500RPM. Everything from 5500RPM and up to max RPM is at 28*. And thats fine. Maybe you don't need a bunch more advance from that point on.
But--lets say you want to increase or decrease the timing in the middle--around 3800RPM. Maybe the advance is currently set at 14* at 3800RPM and you want to set it up to 16* for better throttle transition. So, you lengthen or shorten the rod to gain some advance in the middle.
Haven't you just screwed up the idle and top end timing????