Ericlb, it was my understanding that unleaded gas doesn't make engines drop valves - that it was more a mechanical problem of broken springs; over revving, floating and smacked valves on dome pistons, popped keepers, or a rare 'stuck' valve on an engine that doesn't see much use. Methyl ethyl lead slowed the explosion rate, making cheaper (low octane) fuel possible, and a slower, cooler burn. The faster combustion rate and resulting higher heat of unleaded 89 or less octane fuel tends to 'burn' the edges of exhaust valves and seats, causing compression loss and aggravating the problem as hot (just ignited, highly compressed) combustion gases start leaking through the pitted valves and seats, especially in higher compression engines. Is it possible that a very long term of such abuse could cause a catastrophic valve failure? I suppose, but such an engine would barely run, if at all.
RedDave, the governor is definitely loose in the joints, and that was already on the fix list. Are there specific wear parts in it that should be replaced? or is it best to use a 'shotgun' approach, and replace 'em all?
RFB, thanks for the tips.
I'm thinking that the flat top pistons might be better with unleaded fuel and OEM type valves, even with the 1/8 overbore, which I think I'll do. As was pointed out, it's done ok for at least 25 years with somewhat unleaded fuel (I've been using lead substitute in it, but no guarantees what went on before I got it). Also, might help to retard the timing just a hair from factory spec to compensate for the 'ping' of a faster burning fuel, and get more umph from the bang as well.
Also wondering if anyone has ever come up with a lower first gear set up? I'm sure I'm not the first or only one to think it would be handy to slow it down just a little bit.
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