Hi. Many thanks for the quick replies.
When trying to go forward it will rev up quite happily but either no movement or very slow. The engine doesn't stall and no misfires, load sounds normal. From no movement, if you go into P and then back to D it will sometimes go slowly but if you rev then it doesn't pick up speed. When in P it ticks over quite happily with no probs. The last time I tried to go forward there was a 'grating' sound for a few seconds. The garage that have had it have: put in new electric fuel pump (at rear), new points, condensor, coil, plugs, oil presure switch, changed oil, ballast resitor, fuel filter, contact set, carbs overhauled - needle/jet/ etc, flame trap, advance vacuum, air filters....balance carbs, set up engine timing... The oil pressure has dropped and this coincided with the loss of power, but there is oil pressure. The garage seems to try a 'new part' until it works and then its OK for a while - I got it through the MOT with no probs, put it in my garage and was away for a week, started it up today, drove down the drive from the garages (very narrow so no real speed) and when I got on the road it did'nt want to pick up speed, revs OK,. Pulled into the side, turned off engine, restated and put into D and nothing, turned off ahd a look under bonnet (not sure why as I knew the engine was still there), stated up fine, put into D and grating sound for a second and then slow forward. To get back I reversed into a drive and it seemed Ok, put into D and again didn't really want to move but it did move slowly but needed more revs than it should to keep it moving. Got home, and is now in garage. I'm happy to travel as far as need be to get it sorted.
Many thanks.