The ignition timing dictates where in the piston-travel that the petrol mix is ignited in the cylinder, measured in degrees of rotation of the crankshaft away from the top of the piston-travel (zero being 'Top Dead Centre', TDC). Ignition timing set too early and the engine can 'pink' (pre-ignition, timing too advanced); too late and performance is reduced (timing retarded - and sometimes 'backfiring' or 'popping' begins as the resultant unburnt petrol burns in the exhaust pipe). For a R4, some degrees before TDC are normal - mine is said to be 6 degrees, set at the factory.
Richnd, a strobe-light timing light with adjustable timing may solve your issue. The light timing-adjustment moves the light's flash-point - setting the strobe-light adjusting dial to 6 degrees and pointing it at the flywheel should show alignment between the TDC (zero degrees) mark (the gearbox/bell-housing mark nearest the middle of the engine on the 1108cc) and the single flywheel mark, if the engine timing is currently set at 6 degrees before top dead centre (BTDC).
Using this method means that the other (confusing) timing marks can be ignored, and just use the strobe-light adjustment dial to read the current timing advance. Timing marks on the bellhousing for the 1108cc engine seem to be in one degree steps - zero to eight degrees, though they are tricky to see - especially with fading eyesight resolution (hence my use of the adjustable timing strobe!).
Currently mine is running well at 11 degrees BTDC (which would be off the scale if I used the bellhousing markings) - far more than the 6 degrees 1984 'book' value.
More ignition advance gives the petrol more time to burn fully before being shoved out into the exhaust, but too much advance reduces efficiency as the early petrol burn works more to slow the piston's rise rather than to power it's fall. There will be a sweet spot!