My son came around earlier this week and we took three of my bikes for a ride. That gave me some enthusiasm to attack the project again, so first job was off with the gearbox to cure some oil leaks. Despite all new gaskets and fibre washers during its rebuild, it leaked everywhere. It’s a plunger box bolted to the engine, but is easy to get out because my inner primary is not part of the crankcase. Why did BSA make it part of theirs?
So replaced fibre washers with copper and attacked the camplate spindle. Why it only has a sixteenth wide seat to seal to the case can only be explained by BSA, but is a very poor piece of engineering. Not even enough meat to countersink for an O ring, so I cut a new gasket and used lashings of Hylomar. The oil leak from the mainshaft will continue as they always do.
Refitted the box and then tore off the Mikunis. I really couldn’t face wasting any more time and money on them. Apparently Amal designed them but found whilst they were a good two stroke carb, they were a heap of trouble on four strokes and so sold the design to Japan. Wish I had known that before I bought them.
And so I started fitting the new Amals. I didn’t want to make a cutaway in the side of the petrol tank for the front carb as it would look bad and require a lot of refinishing, but happily I found I could get clearance by machining the carb body. That done, it was a case of modifying the mickey mouse threads Amal use to a more standard M6.
Overall, I am disappointed with the Amal finish. Mikunis appear to be cast from aluminium, are well engineered and have a chrome plated brass slide, whereas the Amals appear to be zinc and their throttle slides are so sloppy I reckon they will rattle at tickover. They really need sleeving – and they are new! But hopefully at least they will be easier to jet than the Miks, where changing one jet affects all the others, meaning every jet change puts you back to square one.
Tomorrow I intend sorting out the rear carb and redesigning the choke cables. And fixing the brake light on the A10 if time permits.