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Grady Clay Grady Clay is offline
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Join Date: Dec 2003
Location: Arapahoe County, Colorado, USA
Posts: 9,032

Good question.

When cold and trying to start the MFI has two (or three for ’69) assists. While the pump only knows throttle position and RPM it is adjusted by barometric pressure via the aneroid and the cold running thermostat. While cranking, there is additional fuel added via the cold start system. For all there is a solenoid valve on top of the fuel filter console that sorta sprays raw fuel down the intake stacks. (’69 has an additional enrichment that forces the MFI pump full flow).

In practice the cold running thermostat has the major influence over the mixture while running cold. The cold start circuit(s) only function while cranking. They are temperature dependent and disable themselves with the thermo-time switches if you crank too long.

To answer your question exactly:
Yes, the MFI pump is starting and running in a very rich mode governed by the cold running thermostat. The throttle position probably doesn’t change the mixture other than normal (I have never measured that) but is very influenced toward rich by the thermostat. There is the additional cold start enrichment while cranking.

ANSWER PRICE LIST (as seen in someone's shop)
Answers - - - - - - - - - - - - - - - - $0.75
Answers (requiring thought) - - - - $1.25
Answers (correct) - - - - - - - - - - $12.50
Old 10-12-2005, 05:48 PM
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