Why do you need a choke in a cold engine?
The choke provides a temporary super rich condition (approaching a ratio of 10:1 or so) which promotes easy starting of a cold engine. The richness is necessary because cold fuel in a cold engine does not vaporize as readily …so the effective richness of a given mixture is reduced.
What happens to choke spring tension as engine warms up?
As the engine warms up, the choke spring tension will be reduced; if the accelerator is moved slightly open, the fast-idle cam will drop a notch and move toward curb (warm) idle RPM. You do not want to aggressively throttle the engine to get the fast idle to drop.
What makes a car hard to start when cold?
Hard to start when cold …requires excessive choking. Lengthy warm-up required. Rough, erratic idle that drifts toward higher RPMs than expected based on the setting of the curb idle screw. Sometimes a lean condition will cause a “hanging” idle that is slow to settle down to set idle speed.
What causes a choke to stay on fast idle too long?
Stays on fast idle too long: The choke spring tension is too tight, the heat source is not being supplied or is blocked, or the fast-idle cam is gummed up, bent or has another problem that does not allow it to drop.
The choke provides a temporary super rich condition (approaching a ratio of 10:1 or so) which promotes easy starting of a cold engine. The richness is necessary because cold fuel in a cold engine does not vaporize as readily …so the effective richness of a given mixture is reduced.
As the engine warms up, the choke spring tension will be reduced; if the accelerator is moved slightly open, the fast-idle cam will drop a notch and move toward curb (warm) idle RPM. You do not want to aggressively throttle the engine to get the fast idle to drop.
Hard to start when cold …requires excessive choking. Lengthy warm-up required. Rough, erratic idle that drifts toward higher RPMs than expected based on the setting of the curb idle screw. Sometimes a lean condition will cause a “hanging” idle that is slow to settle down to set idle speed.
Stays on fast idle too long: The choke spring tension is too tight, the heat source is not being supplied or is blocked, or the fast-idle cam is gummed up, bent or has another problem that does not allow it to drop.