Much fuel leaked under engine when ignition was left on for a short while. Traced fault to front carburettor float valve sticking in down position as the float arm had worn and was not contacting lower travel stop correctly, allowing the valve to fall lower than it should therefore snagging float arm in down position. Initial leak from float bowl overflow pipe, then from starting carburettor. Took a couple of goes to properly rectify problem (had to smooth wear from float arm and also re-shape float arm so it would engage on lower travel limit peg on float bowl upper assembly. Checked rear carburettor float action - fault not evident, lower travel stop works. Cleaned both float bowl inlet filters (front one contained a fair amount of crap). Took a couple of goes to get fuel supply banjo fitting washers to seal correctly. Had to smooth fibre washers flat on emery paper as they had worn and were hard. Need to replace washers soon.