My ES2 came with a monobloc - should be a 276 type. To get up and running I propose to keep the later unit after giving it a good clean and sa set of gaskets.
However I'm slightly puzzled by what the main jet should be. The original would be a 170, but later ES2s with the monobloc specify a 240 - 270 depending on what I read. I'm thinking that 250 or so is a wiser option.
Any views?
Haycroft's "Book of the N…
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Thanks George. As the main…
Thanks George.
As the main jet really only comes into operation at wide open throttle, which I'm unlikely to use much, it's better to err on the large side rather than the small.
As you say, it's unlikely that such a small increase in compression ratio would make that much difference in maximum power. Would the 55 model have had an alloy head, and perhaps bigger valves? It's still specified with the same 1 1/16" carb size.
I suspect the earlier smaller main jet was in the interests of economy rather than power.
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My '55 ES2 has a light al…
My '55 ES2 has a light alloy head. I believe that was the norm for that year. I can't help with the valve sizes. Strangely Amal recommend checking the main jet size first (before the other checks). They state "Test the engine for full throttle. If, at full throttle, the power seems better with the throttle less than wide open or with the air valve closed slightly, the main jet is too small. If the engine runs heavily the main jet is too larger." There you have it!
George
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Haycroft's "Book of the Norton" (essentially a service and maintenance manual) gives the 1955/56 ES2 Monobloc as having a 270 main jet. It gives the main jet for a '52 ES2 (276AU) as 160. Note also that the '52 had a compression ratio of 6.6 whereas in '55 it went up to 6.8 although I can't see that making much difference to the jet size. The power output also increased from 21bhp to 25bhp - hence, presumably, the larger jet.
George