Took the boat out today for a test and the motor ran great. After checking just about everything and not finding out why it wouldn't run at anything but idle I finally found the problem. Someone had fitted a cable clip in the wrong place!! It was restricting the cable movement, and it was the cable attached to the moving plate on the ignition advance -so it wasn't advancing properly when the throttle was opened. Very simple fix, but took me a long time to spot it. Got there in the end though, just need to adjust the transom by a few inches now to lift the engine up as it's a long leg not a short one like the old engine.
Regards
Kevin
Regards
Kevin