Scooterotica

would love to understand the complex relationship between ignition timing, compression ratios, exhaust and port timings when aiming for high BHP, from what i understand seems to be a case of suck it and see

I did a road test once on 210, pm pipe, std carb and found as the ign timing was decreased from say 19 deg to 14 deg the whole power band seemed to widen by 4 or 5 mph, as I was more concerned about pinking at the time, I didnt really think too much about it. Interested now tho`

davidblythe wrote:would love to understand the complex relationship between ignition timing, compression ratios, exhaust and port timings when aiming for high BHP, from what i understand seems to be a case of suck it and see

I think there are so many variables you couldnt draw up a 'table' to show the relationship as every motor is so different.
Since teaming up with Charlie I've learnt loads on the values of egt gauges and proper dyno setup. I know he could explain the complexities of it all. But I dont think I would understand everything tbh.
Everything affects everything from weather to fuel to pipes to comps. Squish clearance, angle, velocity,bowl design, ports. Cooling weight-bike and rider...the list is endless.

Answering the original question

Two reasons for less advance these days . . firstly fuel, secondly if you use elctronic ignition there's less delay at high rpm. This means the timing is effectively more advanced at 6000 rpm than with points ignition. Martin at Chiselspeed gave me this info when I was asking him stupid questions about ignition timings a few years ago.

Special X wrote:... if you use elctronic ignition there's less delay at high rpm. This means the timing is effectively more advanced at 6000 rpm than with points ignition.

yeah, that's a good point, never thought of that.

My Mugello is set around 17º BTDC, after starting at 19, then retarding gradually til the pinking stopped.
of course it could be my carb settings causing the ½throttle pinking, need some more setting up rides really, but had got it pretty much there and just wanted to ride it, so played it safe with the timing.

I'm installing electronic ignition system (BGM stator & Indian flywheel) and little bit confused about "correct" timing advance for my set-up.

I have original SX 200 cylinder, late type cylinder, LTH reed valve and modified two-ring piston. The compression is raised little bit as there's 1 mm spacer at the bottom of the cylinder (without any gasket) and 1,5mm head gasket to compensate the long stroke crankshaft (60mm dl/GP type).

Should I use the advance for SX (23 degrees) with little less advance or should I aim for more dl/GP:ish figures (21 degrees or even less)?

Thanks!

just fitted an Agusto7000 to my monza225. used to pink underload(in 4th) when sitting in the upper rpm, when in the powerband.
on inspection was static previously at 20deg
now with Agusto static at 24deg, retarding to 18deg as revs rise.
not so many miles testing yet, except, smoother low down, less 4 stroking, and powerband seems more pronounced.
so far no pinking when flat in 4th

Whatever the motor needs to not pink.
What I believe will happen in the near future will be some type of fuel injection combined with a computerized ignition system that will anylize and deliver exactly what your engine needs at every rpm.
Think how boring that'll be.