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CB750 K1 Valve Timing Question

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cbxman:
Nigel,

http://forums.sohc4.net/index.php/topic,164119.0.html

This is a long thread.  Checkout reply #27, then go on to #55, then #60.

All very interesting, particularly the arguments over the what the airscrew does!

Also mods to Emulsifier.

Cheers,
Jerry

K2-K6:
I see what you mean on airscrew direction  ;D I'm with MRieck on this one, turning outward makes leaner mixture on these carb.

It's opposite on PD and many CV type as the screw sits between the venturi and the inlet valve in comparison to older type slide carb with screw next to air filter.

K2-K6:
Two tired #62 post is absolutely correct, and checked with exhaust gas analysis too  :)

Amazing they are all missing the Honda setup that brings combustion parity (at tickover)  to the engine via idle circuits and not through absolute setting of carb synchronisation.

Oddjob:
They both can't be correct though Nigel, either it's leaner going in or leaner coming out. My understanding was that going in makes it richer but that's directly contradicted by Marks statement and also by Hondas reps during that time if I've read right, as in #70.

K2-K6:

--- Quote from: Oddjob on May 24, 2022, 01:28:06 PM ---They both can't be correct though Nigel, either it's leaner going in or leaner coming out. My understanding was that going in makes it richer but that's directly contradicted by Marks statement and also by Hondas reps during that time if I've read right, as in #70.

--- End quote ---

Yes Ken, he's wrong as most of us understand it. There's contradiction in the explanation of how a jet flows by reducing below atmospheric in venturi that allows fuel to flow through the jet to the lower pressure area (correct) but that's ignored in explanation of this interaction.

If you had no air at all, then the idle jet would be full flow as soon as you started the engine, and giving no gradient of fuelling at all.
Bringing air into that stream (between float bowl and carb throat) allows air volume to mitigate that full fuel flow as the vacuum would rather suck air (less resistance) than fuel.
Passage more open  (screw out) just allows more air and less fuel. More closed and vacuum portion to fuel line increases and sucks more fuel in proportion to that restriction. 

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