how do you go about tuning the spark table in megasquirt?

The same as manual tuning for fuel - click on tuning (at the top of the screen) , select spark table 1 , then use the left/right and up/down keys to select where you want to change - then it's `e` to increase and `r` to reduce .
Then burn to ECU , close that window , and if it works better then remember to save it .

Correctly tuning the spark map is much harder than tuning the fuel map.

You can tune WOT two ways:
* Advance until it pinks then back it off a couple of degrees.
* Do timed runs in high-ish gear through the revs, trying different advances. Choose the fastest acceleration at each point.

The first doesn't necessarily give you the best power, and the second is prone to error. Only dyno testing will allow you to properly tune this.

Tuning cruise is a bit easier. Lots of advance without the engine surging. On a motorway adjust the spark and fuel until you reach the lowest fuel consumption.

For idle, the more advance you have, the more you need to lower the throttle stop.

Creating a "hole" of lower advance at your idle point will stabilise the idle and allow the engine to rev up more easily.