Capable of 100mph...maybe
In the interests of stopping debris entering the carb intake I had fitted a belmouth with a fine metal gauze screen. This is needed as the carb is a 376 monobloc, as opposed to the correct 276 pre monobloc, which means the origional airfilter cannot be connected up as the rear of the 376 is tight upagainst the frame tube. Anyway, whilst I am aware that this is a sixty year old engine it felt stangled above three quarter throttle. Max speed was about 70 mph in top, more than enough as its starting to 'buzz / high pitched vibration' at those revs and 60-65 is a more comfortable cruising speed. But there was no way it would ever get to that advertised 100 mph. Surely a little bit of gauze screen could not make that much difference?.
Well in the interests of science I fitted a belmouth with no gauze. Went out for a spin and much better, so much better in fact that my GPS phone app recorded a top speed of 88 mph on a quite stretch of rural dual carriageway. The speedo needle still bounces about a bit over 70 mph so I was not quite sure how fast it was until later (honestly officer) and it was only held for a short time. However, I would not say that such speeds are 'comfortable', I was really aware of all the mechanical components doing their stuff. The riders of the fitfties must have had different expectations compared to those of us bought up on japanese 'sewing' machines.
Other updates:
As the miles increase the brakes are getting progressively better, clearly the shoes take some time to bed in.
The primary chain is still tightening up during every ride. I adjust it just right (1/2 inch free play), tighten the bottom pivot bolt and the clamping bolt really tight, adjust rear drive chain (3/4 inch) and twenty miles later primary is tight and rear chain has slackened off. Clearly the gearbox is being pulled backwards by the rear chain. I think I have found the reason. The gearbox bottom pivot bolt passes through a hole in the gearbox casing. If this hole is worn too large the primary chain adjuster, located at the top of the gearbox, rotates the bottom of the box slightly forwards as the chain is adjusted to the right tension. Even though the pivot and clamp bolts are fully tightened the forces produced by the rear drive chain are so great that they pull the bottom of the gearbox rearwards, taking up the play on the worn bottom pivot mount, and tightening the primary chain. Apparently this is a common problem (that I was not aware of). Solution is to remove the gearbox, drill the bottom mounting hole oversize and fit a bush to restore a tight fit for the pivot bolt. SO....this is the job for this week. I will post some pics of the work.
AND finally.....In an attempt to stop the carb getting hot I had installed a 'thick' O ring between carb and manifold, with the carb studs just nipped up enough to compress the O ring leaving about a 50 thou gap between carb and manifold. Well....it worked but I was concerned the seal was not reliable. I have reverted to the origional paper gasket seals but this time with a 'Tufnell' insulator spacer made from a piece of 3mm sheet mateial (you can buy them off the shelf but where's the fun in that)
