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General Minitrail Talk
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S65 carb woes
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<blockquote data-quote="69ST" data-source="post: 189716" data-attributes="member: 5"><p>135psi might be a decent number. Compression gauges can be notoriously inaccurate with displacement this small. If this is an NOS head w/new valves (or NOS), I'd try lapping the valves, before cutting the seats. As long as you can reach uniformly solid metal with the contact band close to being centered (vertically along the valve face) and no more than 1.5mm wide (.8-1.25 would be better), you should be good-to-go. I leak-test using Brakleen, it'll find gaps too small for gasoline. IMO, valves are sealing properly when no Brakleen gets past the valves...using thumb pressure to hold the valve tight against the seat. It's a high standard...and...with new parts, sometimes valve sealing will improve with runtime.</p><p></p><p>As for the liquid fuel you found, are you 100% certain that wasn't a result of fuel slosh + spillage from removing the carb?</p><p></p><p>Don't be fooled by an engine that will fire a rich mixture when cold. You know how pig-rich the mixture gets with the choke closed? Well...it's just as rich when it's needed to cold-start. The explanation is basic...only gasoline vapor burns. When the engine & fuel are cold, only a small fraction of gasoline goes from liquid to vapor state. Once up-to-temp, far more of the fuel vaporizes and the mixture goes truly pig-rich. The same volume of liquid gasoline inhaled can "act" very different due to temperature variations.</p></blockquote><p></p>
[QUOTE="69ST, post: 189716, member: 5"] 135psi might be a decent number. Compression gauges can be notoriously inaccurate with displacement this small. If this is an NOS head w/new valves (or NOS), I'd try lapping the valves, before cutting the seats. As long as you can reach uniformly solid metal with the contact band close to being centered (vertically along the valve face) and no more than 1.5mm wide (.8-1.25 would be better), you should be good-to-go. I leak-test using Brakleen, it'll find gaps too small for gasoline. IMO, valves are sealing properly when no Brakleen gets past the valves...using thumb pressure to hold the valve tight against the seat. It's a high standard...and...with new parts, sometimes valve sealing will improve with runtime. As for the liquid fuel you found, are you 100% certain that wasn't a result of fuel slosh + spillage from removing the carb? Don't be fooled by an engine that will fire a rich mixture when cold. You know how pig-rich the mixture gets with the choke closed? Well...it's just as rich when it's needed to cold-start. The explanation is basic...only gasoline vapor burns. When the engine & fuel are cold, only a small fraction of gasoline goes from liquid to vapor state. Once up-to-temp, far more of the fuel vaporizes and the mixture goes truly pig-rich. The same volume of liquid gasoline inhaled can "act" very different due to temperature variations. [/QUOTE]
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