truck idling really high

[1968CHEVYC10]

the 350 in my truck is idling anywhere from 1500 to 2500rpm, it would do this every once and awhile normally idling around 7-8 hundred rpm, but now It's always like this, I adjusted the idle mixture screws (it's a q-jet) but that made zero difference in the idle speed.

[haysonj]

Originally Posted by 1968CHEVYC10

the 350 in my truck is idling anywhere from 1500 to 2500rpm, it would do this every once and awhile normally idling around 7-8 hundred rpm, but now It's always like this, I adjusted the idle mixture screws (it's a q-jet) but that made zero difference in the idle speed.

Check to see if your secondaries are stuck open, this happens alot on these carbs if the butterfly rods get worn or bent

[hayhauler71]

check the throttle blades [rear] to see if they are stuck or if the choke is kicking on

[1968CHEVYC10]

I just checked the secondaries, both were shut. Should the bottom secondary plates open up when you open the throttle all the way? I couldn't get them to move even with the throttle all the way open and pushing on it with a screw driver. I wouldn't think that would be the high idle problem, but it might be why it always bogs down when I try to get into the secondaries. Anyway how would I check if the choke is kickin on?

[Stocker]

Originally Posted by 1968CHEVYC10

Should the bottom secondary plates open up when you open the throttle all the way?

No -- they are vacuum operated. They'll open as needed when you accelerate, but not if you're just revving it with no load on the engine.

Anyway how would I check if the choke is kickin on?

Take a look at your fast idle cam -- should be on the pass. side iirc; it's curved and has 'steps' on it. If your linkage is up on one of the 'steps', your idle will be fast. This doesn't necessarily mean the choke is on, just that the idle is fast.

[1968CHEVYC10]

Originally Posted by Stocker

Take a look at your fast idle cam -- should be on the pass. side iirc; it's curved and has 'steps' on it. If your linkage is up on one of the 'steps', your idle will be fast. This doesn't necessarily mean the choke is on, just that the idle is fast.

I couldn't really seem to find what you described. here's a pic.

[haysonj]

The bottom one is the one that may be stuck and it will be so slight that you may not be able to see it. The top opens under vacuum the bottom opens under full throttle. It will not open if the choke is partially on. You need to prop the top open with a wrench or something then hold the choke open. Now open the throttle all the way and see if the bottom butterflies open. After that release the throttle rapidly then start it and see if the idle has gone down. If it does your problem is in the secondaries.

[haysonj]

The shaft to the left and above the choke spring is the secondary shaft. You may be able to put a pair of pliers on it and manually close it. It wont take much so don't crank hard on it.

[1968CHEVYC10]

Originally Posted by haysonj

The bottom one is the one that may be stuck and it will be so slight that you may not be able to see it. The top opens under vacuum the bottom opens under full throttle. It will not open if the choke is partially on. You need to prop the top open with a wrench or something then hold the choke open. Now open the throttle all the way and see if the bottom butterflies open. After that release the throttle rapidly then start it and see if the idle has gone down. If it does your problem is in the secondaries.

Ok not 100% sure what I just did but it idles around 800rpm now, so I guess I fixed it. I moved the little lever that keeps the bottom secondaries from opening and then opened the throttle, did that a couple times and then started it. So does that mean there's still a problem somewhere?

[QKENUF4U]

sounds more like a really big vacumn leak to me...

[Mike J]

check for a vacuum leak