Polished Kirkham with V12 engine at London

[Gaz64]

Originally Posted by olddog

Pulling timing lowers Hp, and that's fine to lower the Hp some. If you go too far, in my opinion, that is a poor way to kill power. If you get to the point that you are lighting the fuel so late that a lot of un-burned fuel is going out the exhaust this will make the O2 sensor believe you are lean when you are not. The ECU may compensate and make you burn rich while thinking it is spot on. High over lap cams can do the same thing at idle.

Burning a bunch of fuel after the exhaust valve is open, is a waste of fuel, which might explain your poor fuel mileage. I'm not certain but it might heat the exhaust valve too.

It would be better to tune the engine to run right and just limit the throttle to not open all the way.

Yes, better to run it like a throttle stop class car than to make it pig rich and retarded timing. Get that first 15% correct, and even if you limit the throttle to 50%, it will still be so much nicer to drive.
Gary