Does the distributor have centrifugal advance and is it working? The centrifugal advance mechanism is what increases the advance as the rpms increase.
A carburetted engine with no ECU ideally needs a distributor with both centrifugal & vacuum advance, you can get by without the vacuum advance, as I mentioned earlier, it's a fuel economy feature, not having it will just burn a bit more fuel, but the centrifugal advance is a MUST.