Thanks for all your advice. I changed the rotor arm and checked the timing but it made no difference. Then I checked the fuel flow to the carbs. and found it was 6 gallons an hour. Looking through the SU reference book the pump should be pumping 25 - 30 gallons an hour. I checked the flow before the fuel filter and got 25 gallons an hour. So I replaced the fuel filter with a new one and .... success! It now goes up hills much better.