Sorry I haven't got the specs from the cam. It's the standard 1725 rootes engine from 1966.
Apparently between 8-10degrees is OK. Andy at Kent Cams said if it was up in the 18-20 range, it would need serious attention.
I don't understand what this means "What do the plugs say about their treatment?"
The plugs are fine, if that's what you mean, perhaps a little hot.
It's not the original engineer/tuner who's did the engine, who's going to look at it. It's the same guy who did the Rolling Road on Thursday. He said he would like to spend a bit more time on it. He's certainly well qualified. I think he was just shocked that after doing some work on it, it still ran badly.
My feelings are from everyone I've asked than the cam timing gear is slightly out, and that perhaps the camshaft has been ground too much.
Thanks for all your help, you've been a world of knowledge.
When I talk about your plugs, I am looking for "color".
Your cam specs of 280 degrees (which must be lash to lash) and 8mm lobe lift is no where near what a stock 1725 cam would have been, therefore we cant really talk about it being from a stock 1725 and have it mean anything.
We would like to know the lobe centers (which must be near the 109 degree stock centers), the cam advance (if it exists) and the cam lobe overlap.
You can measure this or get the manufacturer to tell you what it is.
Without knowing this, we have no idea what to expect regarding how this engine should run in the lower RPM regimes, where the peak power might be or how the engine ought to idle.
I am not sure if you dont understand about ignition timing or the folks that you are having things done to your engine but ignition timing is a function, not a point (like 10 degrees is a point).
Making an engine "work" involves getting the timing function so that its endpoint (point where advance has stopped) puts the engine power at the peak power point without detonation.
On the rootes 1725 with 9.2/1 CR, this occurs at 30 to 32 degrees at 3500+ RPM.
Your distributor was likley built for stromberg fed engines, set to 6 or so degrees BTDC at idle. It will have an advance setup internal to the dizzy that says 12 or 13, which correlates to 12 of 13 max cam degrees advance before the advance hits its stops.
12 degrees cam is 24 degrees crank (13 would be 26).
Therefore, a "stock" distributor marked with a "12" internally would want its max timing set to 31 or so degrees, and if the dizzy is functioning to spec, you would have an idle timing of 7 degrees BTDC.
The idle timing is not super important because your engine wont work well in the region between your idle point and max advance timing.
Your engine is not stock, the ignition timing does not work like a stock engine needs and wants. In fact most race engines of the era used a locked out distributor set to the max advance timing (read up on Ak Miller).
We dont just set the ignition to 6,8 or 10 degrees and hope it works out becuase we dont really know how a 50 year old distributor functions with all its wear and tear and shadetree mechanics that have pre-loved our equipment.
BTW a properly modified distributor for "webers" will often only have 15 or so crank degrees of advance, which means the advance internal stop must have some metal added to it and stiffer advance springs fitted. No one uses the vacuum advance on webers becuase there is not a signal suitable coming from the carbs. Idle timing of 16 or so degrees and max timing of 31 will often yield excellent results becuase the VE of your engine is low at lower RPMs and the engine needs more timing till the engine gets on the cam.
This is also why race engines often dont mind having a fixed ignition timing since they need a lot of extra timing till the engine gets on the cam, and once there, the engine usually is not allowed to drop below the point where the advance stops would normally have been.
