Choke/idle question
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Senior User
Joined: May 2010
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From: Richmond, VA
Choke/idle question
I have what may be a stupid question to someone more familliar with carbed vehicles, but i feel compelled to ask it anyway 
Now that it's good and cold outside, there are times I would like to start the truck and let it warm up. I get in, mash the gas to set the choke, and it starts up fine. With the choke engaged, it idles around 1200RPM. As the engine warms, and the choke opens, the RMS rise. Is there a point where the RPMs will/should drop back down to normal by itself? If I tap the gas, it drops down to 800-900 and idles just like it always does, but if i don't tap the gas, they just keep climbing. So far, I have seen them go up to 2500RPM. I didn't have the nerve to see how high they would go without intervention, so I hit the gas. Is this normal? I'd love to be able to allow it to warm unattended, but not if the engine is going to rev itself to death.
Now that it's good and cold outside, there are times I would like to start the truck and let it warm up. I get in, mash the gas to set the choke, and it starts up fine. With the choke engaged, it idles around 1200RPM. As the engine warms, and the choke opens, the RMS rise. Is there a point where the RPMs will/should drop back down to normal by itself? If I tap the gas, it drops down to 800-900 and idles just like it always does, but if i don't tap the gas, they just keep climbing. So far, I have seen them go up to 2500RPM. I didn't have the nerve to see how high they would go without intervention, so I hit the gas. Is this normal? I'd love to be able to allow it to warm unattended, but not if the engine is going to rev itself to death.
Laughing Gas
Joined: Feb 2010
Posts: 781
Likes: 8
From: Sanford, NC
The idle will normally rise when the fast idle of the choke is engaged as the engine warms
up it runs more efficiently. The idle won't go up anymore after it reaches a certain point.
I think 2500 rpms would be about the limit depending on how your fast idle adjustment
is set.
up it runs more efficiently. The idle won't go up anymore after it reaches a certain point.
I think 2500 rpms would be about the limit depending on how your fast idle adjustment
is set.
Thread Starter
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Senior User
Joined: May 2010
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From: Richmond, VA
Would adjusting the fast idle screw affect anything besides this behavior? I'd really prefer it stick around 2k, but I don't know what else the fast idle adjustment does, if anything.
Yes, it's an electric choke. It's adjusted so that it's just closed when it's cold out. I don't think how early or late it opens has any effect on how high the idle goes, just how quickly the revs rise.
Yes, it's an electric choke. It's adjusted so that it's just closed when it's cold out. I don't think how early or late it opens has any effect on how high the idle goes, just how quickly the revs rise.
Laughing Gas
Joined: Feb 2010
Posts: 781
Likes: 8
From: Sanford, NC
You can back off the screw that hits the fast idle cam and it will slow down the idle
speed and it won't have any effect on how fast the choke opens. When the choke
plate starts to open it takes the spring pressure off of the cam so when you hit the
throttle it releases the fast idle cam and the engine idles normally if it is warmed up
enough. The fast idle cam usually has at least two steps in it. This means you can
blip the throttle after it has started but before it is completely warmed up and the
the fast idle screw will engage the second step on the cam which will let it idle at a
lower speed which will let the engine warm up at a more moderate idle speed.
speed and it won't have any effect on how fast the choke opens. When the choke
plate starts to open it takes the spring pressure off of the cam so when you hit the
throttle it releases the fast idle cam and the engine idles normally if it is warmed up
enough. The fast idle cam usually has at least two steps in it. This means you can
blip the throttle after it has started but before it is completely warmed up and the
the fast idle screw will engage the second step on the cam which will let it idle at a
lower speed which will let the engine warm up at a more moderate idle speed.
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