Pretty in Pink, dunno why
Join Date: Feb 2009
Location: Redondo Beach
Both, if I understand your question correctly.
If you start the bike without cracking the throttle, the carburetor is set up to allow a bit of air to pass the butterfly valve (which is what the throttle cables operate). That bit of air passes through the venturi and creates a low pressure over the needle jet and gas is drawn through the main jet in the proper ratio for good combustion at idle.
If you start the bike with the throttle cracked, then even more air is let through, drawing even more gas. The higher RPM creates more air velocity (the piston draws in more air on the intake stroke) and thus a more vacuum, which raises the slide. That allows more opening in the needle jet/mainjet, which draws more fuel to create the proper ratio once again.
However, you may be asking very specifically "What does cracking the throttle do?". Looked at that way, the throttle opens the butterfly valve, which allows more air in. The carburetor takes care of adding gas to the whole mess. Compare and contrast that to a pumper carb (like the CVK40 found on the older Vulcans). In that case, the throttle operates the butterfly valve to add air and also operates a pump to shoot a bit of fuel into the venturi, so that's a carb that truly does both.
Tom [email protected]
On the way downtown I stopped at a bar and had a couple of double Scotches. They didn't do me any good. All they did was make me think of Silver-Wig, and I never saw her again.
'How' are words so important they cannot be too often used.
Sting like a butterfly.
Noli Timere Messorem
Last edited by Tom Schmitz; 09-03-2014 at 07:41 PM.