ENGINE LACKS ‘OOMPH’ AT FULL POWER

1 Basic checks

If pressing the throttle brings a booming noise but little progress, check the ignition timing. Then check the float level’s not too low. Ensure the main air and fuel jets and emulsion tubes are clear.

2 Enrichment valve linkage

If the carb has a full-load enrichment system (often flatteringly called an ‘economiser’) check the valve, if fitted, opens at the correct time. It’ll be linked to the throttle, perhaps with a threaded bar.

3 Enrichment nozzle

Some economisers rely on engine vacuum alone to draw fuel through a nozzle high up in the carburettor throat. The drilling is tiny, so check carefully and make sure it’s not loose or blocked.