ES2 carburettor

Did the rebuild include new valve guides?,  they can be too close fitting and hold the ex valve off its seat . Usually ok till  pulling uphill.

I tried a 389 on a stock ES2 many years ago and fiddled with jetting. Was not an improvement at all.  I'm at 12' above sea level.

I'm sure we have been here before, Richard.

My advice would be as it was before.

I run my ES2 with a 928 concentric. The only difference with this carb is that the main jet should be smaller, on here it is a 240. Goes perfectly well at that in the Vale of York, so about sea level.

You may have been confused with my Poor man's Manx, same engine but 930 carb and hence 230 main jet. Again, it goes very well. Both ES2 engines 1960 and 1959.

Picture 1960 ES2 on North Yorkshire Moors @ 1,325 ft elevation. (Yes I know)

... a 376 1.1/16" monobloc on my 1952 ES2 with similar settings to yours. Initially it had a number 4 cutaway but a 3.5 improved pickup no end. I'm very happy with its performance.

I have a Monobloc carb set up to the 1961 workshop spec on my 1961 ES2. It runs great, starts on first kick and has been the easiest part of bringing this ES2 back to life. I'm about 1200 ft above sea level in Northern Wisconsin, U.S.A.