15-05-2021, 02:43 AM
Started up the old lass (1936 tourer) so as to check a possible gearbox problem. Usually starts on the first or second swing of the crank handle but then I had to use the starter and the engine backfired and would not accelerate smoothly and lacked power so straight back into the garage. A bit strange since it was only a day or two earlier I did a 14 mile run with no problems. Took the plugs out and found some hard deposits which were interfering with the spark gap and cleaned them and checked the gaps. When taking the plugs out Nos 1 and 4 were hot to the touch but Nos 2 and 3 were only warm. I have been running the engine in since the last overhaul (260 miles ago) and I thought that perhaps the carbon deposits were extensive and causing pre-ignition so removed the head and the manifold. The deposits were not particularly bad and were fairly soft but I cleaned them off. Valve seatings looked good and clean. Checked valve clearance and found that several valves had slightly more than the proper clearance by a few thou. Everything looked good so reassembled the head etc. Started the engine and, as before, it did not start easily and backfired through the carby again. Did not sound quite right and did not rev nicely when the accelerator was pressed. Shut it down after a few minutes and again noticed that that plugs 1 and 4 were hot but 2 and 3 only warm. Having taken the plugs out and laid them aside, the chances of the same plug going back into the same hole is pretty remote so I think the plugs are ok. Ignition timing checks out, points gap is ok. Wot, i ask, could be wrong.