[Zman]

I agree with you assuming the bikes has correct compression for the fuel. Typical GG bikes have lower compression and as noted above most of them need to have the head milled to adjust squish and volume. I have added as much as 5mm of timing (measured at the base plate adjustment screws) for stock GG 250 and 300 bikes with uncut heads. While it does give a nice bump in low end performance it did not make a huge difference in high rpm. I suppose that could be because the GG port timing already is focused on low rpm operation or the older stock CDI units limited high rpm operation.

I fully agree you have to be aware of the detonation and retard the timing or increase octane rating to compensate. Also when you are on the edge of detonation jetting is very important. A richer air fuel mixture will run cooler.

I started another thread a week ago regarding the CDIs and my findings are similar to what you are saying and showing in your graph. The CDI curves make a bike difference in the overall power band. I also found when I used the 125 CDI on my 300 it made a huge difference, but I believe the low rpm timing of the 125 CDI plus my 3mm advanced initial timing was too much and it made the bike prone to stalling at low low rpm lugging up technical hills.

With the stock 2000 brick style CDI on my big bore xc300 (now 327) the bike had a very mellow power band and it would not rev as high as other 300s. With the 125 CDI it came on the pipe right off idle, had a big hit in the middle rpm and revved at least 1000 rpm higher than prior. Off idle I did detect a slight hint of detonation so I switched to a newer 300 CDI that had seemed to be a great compromise between the 125CDI and the original brick 2000 XC300 CDI. I later found I needed to put the initial timing back closer to stock with the newer 300 CDI to regain my very low rpm luggability.