[PeteKz]

Timing will make a big difference in fuel consumption and torque.

The more important timing measurement is not at idle, but at full mechanical advance. At full advance (without the vacuum connected) it should be around 28-30 degrees BTDC. If that causes your idle timing to be off, don't worry about it. Just get the full advance timing right. When you connect the vacuum, that should pull about another 10 degrees of advance. Thus, your total timing at part throttle and above 4000 RPM, should be about 38-40 degrees.

This may be higher than what the specs call for on your RoW car. Don't worry about that either. Adjust your timing 1-2 degrees more advanced, and then less advanced, to see where it runs best, without getting into pinging (detonation). If you have doubts, it's always safer to run a little less advance, than too much.

Exhaust popping: Does your car have the thermal reactors and air pump? If so, this could be the cause. You need both unburned fuel AND excess air to get popping or "afterfire". The thermal reactor system injects extra air to help ensure exhaust is fully burned, but if you have excess fuel, then you will get popping.

If your car does not have the thermal reactor, then you may have leaking exhaust gaskets.