An update on this:
I thought I was onto something with the ACR, but upon further investigation I found that adjusting the exhaust valve clearance doesn't actually seem to make any difference. I think I must've imagined an improvement the first time I did it.
After some
lengthy investigation and troubleshooting, I determined that it's actually a carburettor problem. If I block the idle jet with a small piece of wire carefully secured in place, the engine runs perfectly (not at idle though
) and both spark plugs come out clean. I think what must be happening is that the idle circuit is somehow dripping liquid fuel into the intake manifold while running, and that was making the mixture uneven between the two cylinders. Cutting it off means it runs leaner as a whole but I don't think it makes much difference to the mixture at full throttle.
It makes sense as I could always see a bit of liquid fuel sitting in the intake manifold after removing the carb. And it was using a LOT of fuel.
I still need to figure out why the idle circuit is causing this problem... but it's good I didn't spend money on a camshaft and open up the engine for no reason.
RLP
