Fast idle is slow to come on

[K10-Kansas]

Hi all! When I start my truck it idles at 600 for about 30 seconds and then the idle climes to 1300 over a duration of about 10 seconds. Then I tap the gas and put it in gear and go.

I'm pretty sure that a few years ago, I'd start it in the morning and it would go into fast idle immediately, and then after 30 seconds, I'd tap the gas, put it in drive and go.

The way that it is acting now, fast idle is pointless because the truck is warmed up by the time fast idle kicks on.

I have a 2nd Gen, 5.7 V8, Blueprint crate engine with 3,000 miles with a Holley 600 CFM 4 barrel with electric choke, and vacuum secondaries - 4160. Blueprint said this is similar to a stock 1986-87 GM setup.

I've looked at the fast idle cam, screws, etc and everything looks good. The idle speed is not the issue, just that it doesn't go into fast idle until 30 seconds after start. That's not normal right?

[geezer#99]

Your choke is set too rich.
Adjust it leaner.

[K10-Kansas]

Originally Posted by geezer#99

Your choke is set too rich.
Adjust it leaner.

It definitely had been in the past. I had the idle mixture screws out 1.75 turns because that was where the engine created the most vacuum, but I was having backfiring through the carb once mor twice daily, increased soot in the exhaust pipe and a very fast start up first thing in the morning. So I bought at air/fuel gauge and installed it. It was showing 10 at idle so I adjusted it to 14. So supposedly that is good now. To keep the air/fuel gauge at 14 I could only adjust the screws 0.75 out total.

Now that that is supposedly good, I ordered new spark plugs and plan to clean the card and so a sea foam treatment in the gas tank next week.

[geezer#99]

Not being a smart a—-s, but do you know how to adjust your choke?

[K10-Kansas]

Originally Posted by geezer#99

Not being a smart a—-s, but do you know how to adjust your choke?

I have watched several videos on how to, but I have never done it before. Is it possible that a choke adjustment would allow the fast idle to kick in at start up instead of what it's doing now, engaging 30 seconds after start up?

[geezer#99]

Your fast idle is already set. Your choke blade being excessively closed won’t let the idle come up. As the choke coil warms up it forces the choke blade open. Motor runs leaner and the idle naturally increases.
A simple test for you.
Start it up stone cold. Pop aircleaner lid off. Fire it up and quickly open the choke blade enough to get the rpm to increase. Use a long screwdriver to push on the blade. Might only need to open it a 1/4 inch.
Easier to do this with two people maybe.

[K10-Kansas]

Originally Posted by geezer#99

Your fast idle is already set. Your choke blade being excessively closed won’t let the idle come up. As the choke coil warms up it forces the choke blade open. Motor runs leaner and the idle naturally increases.
A simple test for you.
Start it up stone cold. Pop aircleaner lid off. Fire it up and quickly open the choke blade enough to get the rpm to increase. Use a long screwdriver to push on the blade. Might only need to open it a 1/4 inch.
Easier to do this with two people maybe.

Okay thanks. I'll try that later today.

So it's possible that adjusting my choke so that it doesn't close as far as it is on start up, would allow the fast idle cam to engage right at start up?

[geezer#99]

The fast idle cam is engaged as soon as you tap the throttle.

[theastronaut]

Originally Posted by geezer#99

The fast idle cam is engaged as soon as you tap the throttle.

This. When cold, you press the pedal to the floor once before starting to trip the linkage to engage the cold start/fast idle throttle stop and close the choke flaps. Then you start it.


If the choke flap gap and fast idle speed are set correctly it should idle just a little faster than normal, and the flap being closed just the right amount will add the extra vacuum in the carb throat to enrich the mixture. Too far closed and it'll die from being overly rich.

Depending on what carb it is, some fully close the choke flap initially (engine off) then a vacuum dashpot pulls the flap open slightly once it's running (using manifold vacuum) so that it gets a lot of instant/initial vacuum/enrichment while cranking over to start faster, then the gap opens up as soon as it starts to keep it from running too rich at higher engine speed than cranking. Then the choke element warms up to slowly lean out the mixture as it warms up.

The idle mixture screws should be set once its fully warmed up with the choke fully opened. Then, you let it cool off and adjust the choke tension/opening gap to suit how much richer it wants to be at cold start- this will take some trial and error as it has to be fully cold with a fully cold choke element whenever you're doing the adjustment.

[K10-Kansas]

Originally Posted by geezer#99

Your choke is set too rich.
Adjust it leaner.

When I first read this, I was mistaking thinking about the fuel/ air mixture screws. Sorry, I see you were talking about the choke being too closed at startup. Thanks! I adjusted it a bit and started it and the RPMs were sounding better on start up. I'll give it a proper try in the morning. Thanks a ton! That was an easy fix.

[K10-Kansas]

Originally Posted by theastronaut

This. When cold, you press the pedal to the floor once before starting to trip the linkage to engage the cold start/fast idle throttle stop and close the choke flaps. Then you start it.


If the choke flap gap and fast idle speed are set correctly it should idle just a little faster than normal, and the flap being closed just the right amount will add the extra vacuum in the carb throat to enrich the mixture. Too far closed and it'll die from being overly rich.

Depending on what carb it is, some fully close the choke flap initially (engine off) then a vacuum dashpot pulls the flap open slightly once it's running (using manifold vacuum) so that it gets a lot of instant/initial vacuum/enrichment while cranking over to start faster, then the gap opens up as soon as it starts to keep it from running too rich at higher engine speed than cranking. Then the choke element warms up to slowly lean out the mixture as it warms up.

The idle mixture screws should be set once its fully warmed up with the choke fully opened. Then, you let it cool off and adjust the choke tension/opening gap to suit how much richer it wants to be at cold start- this will take some trial and error as it has to be fully cold with a fully cold choke element whenever you're doing the adjustment.

Thanks. I appreciate the info.

[geezer#99]

Originally Posted by K10-Kansas

When I first read this, I was mistaking thinking about the fuel/ air mixture. Sorry, I see you were talking about the choke being too closed at startup. Thanks! I adjusted it a bit and started it and the RPMs were sounding better on start up. I'll give it a proper try in the morning. Thanks a ton! That was an easy fix.

For adjustment of the choke, which way did you rotate the choke coil cap?

[K10-Kansas]

Originally Posted by geezer#99

For adjustment of the choke, which way did you rotate the choke coil cap?

Man, I had so much trouble turning that thing, I don't remember if it ended up being clockwise or counterclockwise. I realized after a minute that I needed to back the choke housing screws pretty far out to allow it to turn more easily. I started the truck this morning and it jumped straight to fast idle. Seems perfect now. Thanks!

[scottofksu]

Originally Posted by geezer#99

For adjustment of the choke, which way did you rotate the choke coil cap?

This is true for many carbs but probably not all:
More Choke? = Counterclockwise Turn/Left
Less Choke? = Clockwise Turn/Right

[K10-Kansas]

After tweaking the electric choke a bit it worked better but then the next day it went back to not working well so I put on a manual choke and adjusted the fast idle cam out of the way. I've been running it like this for several days and it's great! I pull the choke based on the temp and how long the truck has been sitting and let it warm up, put it in gear, pop the choke mostly in, and then after a minute pop it all the way in. Perfect!

[AussieinNC]

In the pic of the finished choke cable on the carb, it looks like the cable inner end is hitting that rubber vacuum tube coming off the intermediate block on the carb.

Maybe a little twist upwards on the end will let it clear the rubber tube.

IMHO, cable chokes are the easiest way to install a theft deterrent...just pull it out after shut down and most burglars would never know why the truck just wont accelerate. hahahaha

[K10-Kansas]

Originally Posted by AussieinNC

In the pic of the finished choke cable on the carb, it looks like the cable inner end is hitting that rubber vacuum tube coming off the intermediate block on the carb.

Maybe a little twist upwards on the end will let it clear the rubber tube.

IMHO, cable chokes are the easiest way to install a theft deterrent...just pull it out after shut down and most burglars would never know why the truck just wont accelerate. hahahaha

I ended up trimming an inch off thanks.