Can someone explain Cold advance?

[jlwoods99]

I pulled the cap off of a IP I have sitting here to see how the fuel shutoff was and saw the cold advance solenoid. I couldn't see that the cold advance solenoid did anything. With no power on it I couldn't get air to go through the fuel overflow back to the filter. When I applied power it seemed to open a valve to the fuel line. Doesn't make sense to me. Hoping someone can explain whats supposed to happen.

jim

 

[Ugly Moosling]

There's a ball and spring in the return fitting that screws in the top cover of the pump. This acts as a pressure regulating valve and keeps case pressure at around 8-10 psi. When the cold start solenoid is energized it pushes the ball off of its seat allowing the case pressure to drop to 0-1 psi. This pressure change allows the timing to advance a few degrees to help warm up a cold engine.

 

[jlwoods99]

Okay that makes sense,

thanks!
jim