Ignition timing BTDC on Volvo B21A motor

[ademonrower]

Volvo 245 1979-1980 model with B21A (carburetor) engine. The specs in my workshop manual, and in the volvo official specs, say that this engine should be set to 12 degrees before TDC when idling warm at 850 rpm with vacuum hose disconnected and the vacuum port on the distributor plugged with a bung of some sort. So, after replacing the points with electronic hall-effect sender on the distributor, I re-set the timing with a strobe light excactly under the conditions mentioned above. I have pretty much exactly 12 degrees BTDC timing now, and (stupidly) I didn't check the timing before I replaced the points with electronic ignition. Anyway, that shouldn't really matter, because I just want to get the timing "right". Since doing the work, I am noticing somewhat increased gas consumption, and I wondered whether I can go a little higher than 12 deg. BTDC in the interests of increasing engine efficiency without causing engine damage. Any ideas? Thank you!