Idle intermittently high

[K10-Kansas]

Edit: Here's my engine https://www.summitracing.com/parts/m...xoCKRsQAvD_BwE

Hi. I bought a 1971 C10 GMC and had a 350 crate engine put in. When you first start it it idles at a high rpm and if you try to put the truck in reverse or drive while it's doing this, it dies. Letting it sit and idle at a high rpm for 1 or 2 minutes sometimes let's it move to a normal rpm and sometimes not and it will just continue to idle high. Tapping the gas also sometimes moves it to a normal ramp but sometimes not.The out of state mechanic says that this is normal and is trying to get out of doing warranty work. Honestly I give up on him anyway and don't want to drive a state away for fixes. I'd rather fix it myself. What could be possibly causing this high idle?

[geezer#99]

First thing, welcome to the forum!
Now let the fun begin!

Pics of your motor always help.
What 350? From where? Who was the builder?
What carb?
What intake?

There’ll be lots of questions.
Did I mention pics?

[A1971Blazer]

without any specific information...
make sure the throttle spring has enough tension to keep it closed....
check the choke and high idle setting and also make sure there is no binding of the choke linkage....
it should idle high for a few minutes at cold start then back off as the engine comes up to temperature.....
again.....more info is necessary for internet troubleshooting....maybe even a short video while it's doing it...

[K10-Kansas]

Originally Posted by geezer#99

First thing, welcome to the forum!
Now let the fun begin!

Pics of your motor always help.
What 350? From where? Who was the builder?
What carb?
What intake?

There’ll be lots of questions.
Did I mention pics?

Thanks, happy to be here. Sounds good, I'll update the post when I get home from work today.

[Accelo]

If the carburetor is used the issue could be worn butterfly bores.
I would also recommend disconnecting the carburetor linkage and confirming the linkage moves smoothly. Lubricate any pivot points.

[dmjlambert]

You probably have a fast idle spring and lever setup on your carburetor that is tied in with the choke. On my Quadrajet for example, the lever has several steps with varying amount of faster idle. When I press the gas pedal before start and if it is cold outside, the lever moves to the maximum position. Then I start the engine. As the engine warms up, if I press the gas pedal, when I release the gas pedal it may move to a lower step and idle a little slower. If I don't touch the gas pedal it will stay on high idle forever. When fully warmed up, the last step on the lever is used when releasing the gas pedal, which is normal idle. Getting to full warm up depends on the weather. It may take more than a very brief and light tap of the gas pedal to make it go down one or several steps. I am able to drive my truck, and I believe it is normal to be able to drive, when it is fast idling and when still warming up.

[K10-Kansas]

Originally Posted by Accelo

If the carburetor is used the issue could be worn butterfly bores.
I would also recommend disconnecting the carburetor linkage and confirming the linkage moves smoothly. Lubricate any pivot points.

The engine and carburetor are brand new. They don't have more than a mile on them. I haven't been able to drive it yet due to low voltage issues. I'm putting in a wiring harness at the moment.

[K10-Kansas]

Originally Posted by dmjlambert

You probably have a fast idle spring and lever setup on your carburetor that is tied in with the choke. On my Quadrajet for example, the lever has several steps with varying amount of faster idle. When I press the gas pedal before start and if it is cold outside, the lever moves to the maximum position. Then I start the engine. As the engine warms up, if I press the gas pedal, when I release the gas pedal it may move to a lower step and idle a little slower. If I don't touch the gas pedal it will stay on high idle forever. When fully warmed up, the last step on the lever is used when releasing the gas pedal, which is normal idle. Getting to full warm up depends on the weather. It may take more than a very brief and light tap of the gas pedal to make it go down one or several steps. I am able to drive my truck, and I believe it is normal to be able to drive, when it is fast idling and when still warming up.

Oh, hmmm.... The mechanic did mention that if I pres the gas before starting it would have a different idling behavior as opposed to not touching the gas pedal before starting. I wonder if my truck is actually behaving as intended then.

[Tom70C20]

Does it have an electric choke? If so, check to make sure the wire is connected and has power. The electric choke can be adjusted by loosening the screws and turning the mechanism to increase or decrease how "quickly" it opens.

[Tom70C20]

Originally Posted by K10-Kansas

Oh, hmmm.... The mechanic did mention that if I pres the gas before starting it would have a different idling behavior as opposed to not touching the gas pedal before starting. I wonder if my truck is actually behaving as intended then.

Yeah, sounds like it may be normal. Step on the gas before starting to set the automatic choke. It will idle higher longer when it's cold out. Tap the gas as it warms until the idle gets down to normal and then drive away.

Man I feel old right now....

[geezer#99]

New motor!
Was it broke in correctly?
Do you know the break in procedure?
2000 rpm for 20 minutes scenario!

[K10-Kansas]

Originally Posted by Tom70C20

Yeah, sounds like it may be normal. Step on the gas before starting to set the automatic choke. It will idle higher longer when it's cold out. Tap the gas as it warms until the idle gets down to normal and then drive away.

Man I feel old right now....

I think the part that seems so odd is 1) just how high it is idling and 2) how even though it can be running for several minutes, if I shut it off and then need to restart it a few minutes later, it revs high again and 3) then tapping on the gas sometimes doesn't get it to idle normal and 4) it dies if I put it in drive or reverse while it's idling high.

It has been 30 years since I've driven an older vehicle but I don't remember my 72 nova acting this way back in 92. Thanks for your help on this. I wish I could test it more but right now am putting in a complete wiring harness.

[K10-Kansas]

Originally Posted by geezer#99

New motor!
Was it broke in correctly?
Do you know the break in procedure?
2000 rpm for 20 minutes scenario!

I'm sure the mechanic didn't do much other than the bare minimum. So far, the only break in I've done was drive it onto a trailer, then off the trailer, then into my garage, and back out once to turn it around to back into the garage. The mechanic put in the engine and I'm putting in a wiring harness. So I should run it for 20 in in the driveway in park with the engine at 2000 RPMs? Thanks for your help on this.

[geezer#99]

Nah! You’re good!
The engine specs where confusing.
I had to read a little better to see it’s a roller cam motor. They don’t need the critical break in procedure.
Thought you were gonna post some pics of your motor. Prying eyes can see things your mechanic fudged on.

[K10-Kansas]

Originally Posted by geezer#99

Nah! You’re good!
The engine specs where confusing.
I had to read a little better to see it’s a roller cam motor. They don’t need the critical break in procedure.
Thought you were gonna post some pics of your motor. Prying eyes can see things your mechanic fudged on.

Thanks. I tried but can't figure out how to post pictures.

[geezer#99]

Try this.


https://67-72chevytrucks.com/vboard/...d.php?t=712252

[72SB]

OP

You have a BPE motor, excellent motor. There would have been a full packet of info for the motor stapled to the crate it came in.

Contact BPE tech dept, give them the ID # of the motor you have (its on DS of block). If the "mechanic" didn't give you the packet BPE has a file on it and can send duplicate. they dynoed the motor, its already broken in

I believe they use 600 cfm holly carb. Sounds like you just need some minimal adjustments. If it is an electric choke you need IGN power to it

If you have the skills, a vacuum gauge, timing light and a tach (some timing lights have them) will get you dialed in

Sounds like the chole is either not working or carb does not have one.

Just contact BPE tech and they will give solid advice. That motor has a warranty

[K10-Kansas]

Originally Posted by 72SB

OP

You have a BPE motor, excellent motor. There would have been a full packet of info for the motor stapled to the crate it came in.

Contact BPE tech dept, give them the ID # of the motor you have (its on DS of block). If the "mechanic" didn't give you the packet BPE has a file on it and can send duplicate. they dynoed the motor, its already broken in

I believe they use 600 cfm holly carb. Sounds like you just need some minimal adjustments. If it is an electric choke you need IGN power to it

If you have the skills, a vacuum gauge, timing light and a tach (some timing lights have them) will get you dialed in

Sounds like the chole is either not working or carb does not have one.

Just contact BPE tech and they will give solid advice. That motor has a warranty

Oh, yeah, I found it in the cab today. Yup, it's an electric choke. I'll go look up some videos on the choke.

[K10-Kansas]

Here are some pics of the engine.

[72SB]

yes you have a EL choke and I see it is wired....You would have yo meter the wire to see if its is getting 12vdc

However your wiring does look sketchy in general but if you get 12v to it, than it will work

On a cold engine you should just hit gas once to close the choke then start with abour 1/2 pedal

I would get some plug wire management, so you don't burn one on the headers

[K10-Kansas]

Originally Posted by 72SB

yes you have a EL choke and I see it is wired....You would have yo meter the wire to see if its is getting 12vdc

However your wiring does look sketchy in general but if you get 12v to it, than it will work

On a cold engine you should just hit gas once to close the choke then start with abour 1/2 pedal

I would get some plug wire management, so you don't burn one on the headers

Great, thanks for the tip. I'll go through the truck and make sure everything is setting in a safe spot. Thanks for catching that wire being too close to the header. I'll have to wait on the 12V test. I have started pulling all of the wiring and got a complete wiring harness from American AutoWire.

[72SB]

AAW makes a nice kit. While you are on wiring mode, consider a headlight relay harness. Not only will your headlights be brighter, all your lights will be. I got mine from LMC

Takes the full 12vdc load off the light switch

[K10-Kansas]

Originally Posted by 72SB

AAW makes a nice kit. While you are on wiring mode, consider a headlight relay harness. Not only will your headlights be brighter, all your lights will be. I got mine from LMC

Takes the full 12vdc load off the light switch

Great idea. I see they are only 24 bucks.

[Steeveedee]

Originally Posted by 72SB

yes you have a EL choke and I see it is wired....You would have yo meter the wire to see if its is getting 12vdc

However your wiring does look sketchy in general but if you get 12v to it, than it will work

On a cold engine you should just hit gas once to close the choke then start with abour 1/2 pedal

I would get some plug wire management, so you don't burn one on the headers

First thing I noticed was those plug wires needing some attention.

OP- I'm not seeing a distribution block/proportioning valve assembly next to the master cylinder. Was it like that when you got it? Or am I just blind?

[geezer#99]

Originally Posted by Steeveedee

First thing I noticed was those plug wires needing some attention.

OP- I'm not seeing a distribution block/proportioning valve assembly next to the master cylinder. Was it like that when you got it? Or am I just blind?

Definitely blind!
It’s on the frame crossmember down by the rad.