Carb/idle quesion
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More Turbo
Joined: Mar 2022
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Carb/idle quesion
new problem unlocked.
Truck's been on a lift for several months while I'm knocking out body work on the bed/hood etc.
Recently pulled the truck off the lift and drove it to the end of the driveway to turn it around and back it into the garage. When put in reverse, engine stumbled and died. I thought it was possibly a low fuel issue and the truck fired right up again and would idle just fine until it was put in gear again.
If I reved the RPMs in park or neutral, then dropped it into gear, it would start moving and I was able to give it enough gas to keep moving.
I just hooked up my tach (was doing some rewiring) and I've adjusted the idle set screw on the carb to around 1200RPM in order to keep the engine from stalling when put into gear.
I don't recall this being an issue in the past.
Pertinent info
400ci, 650 CFM Holley carb, C6 transmission that was just rebuilt by a shop, engine warmed up with choke open.
I've read this might be a cracked vacuum line, failing torque converter (I hope not), or possibly something else.
Any suggestions?
Truck's been on a lift for several months while I'm knocking out body work on the bed/hood etc.
Recently pulled the truck off the lift and drove it to the end of the driveway to turn it around and back it into the garage. When put in reverse, engine stumbled and died. I thought it was possibly a low fuel issue and the truck fired right up again and would idle just fine until it was put in gear again.
If I reved the RPMs in park or neutral, then dropped it into gear, it would start moving and I was able to give it enough gas to keep moving.
I just hooked up my tach (was doing some rewiring) and I've adjusted the idle set screw on the carb to around 1200RPM in order to keep the engine from stalling when put into gear.
I don't recall this being an issue in the past.
Pertinent info
400ci, 650 CFM Holley carb, C6 transmission that was just rebuilt by a shop, engine warmed up with choke open.
I've read this might be a cracked vacuum line, failing torque converter (I hope not), or possibly something else.
Any suggestions?
Lead Driver
Joined: Jun 2006
Posts: 5,654
Likes: 979
From: Near Yosemite CA
More than likely, after sitting for months as you said, your carb has "gummed up" I've had good luck with Seafoam for issues like that, check all your vacuum caps, seems the newer rubber degrades much faster than the old ones. I would not blame it on torque converter, more than likely just bad/old gas and gummed up carb, depending on how much fuel is in the tank, I would add a heavy dose of Seafoam and let it run.
Lead Driver
Joined: Jul 2017
Posts: 9,597
Likes: 1,172
From: San Jose, CA
And while you’re idling, if you can adjust it back down to normal idle range below 1000, check for vacuum leaks with a spray of some kind.
Carb cleaner, brake cleaner, WD-40, or just water. Any change in idle and you found one leak.
Could be more than one.
Could be something with the transmission, but I would rule everything else out first.
Check your ignition timing. Bump it up a little bit maybe, and see if that helps.
Change from manifold to ported, or vice versa, depending upon which way you have it now.
Just to see if things change.
Also, see if it does it with the choke partially closed. Helps to rule out an overly lean mixture.
This could be caused by carburetor issues, or the aforementioned vacuum leaks.
Carb cleaner, brake cleaner, WD-40, or just water. Any change in idle and you found one leak.
Could be more than one.
Could be something with the transmission, but I would rule everything else out first.
Check your ignition timing. Bump it up a little bit maybe, and see if that helps.
Change from manifold to ported, or vice versa, depending upon which way you have it now.
Just to see if things change.
Also, see if it does it with the choke partially closed. Helps to rule out an overly lean mixture.
This could be caused by carburetor issues, or the aforementioned vacuum leaks.
Lead Driver
Joined: Jul 2017
Posts: 9,597
Likes: 1,172
From: San Jose, CA
A weak spark can cause it as well. You never know what gets hold on these things, but I would still just mess with the timing a bit.
You’re not still running a points distributor by any chance, are you?
You’re not still running a points distributor by any chance, are you?
Lead Driver
Joined: Jul 2017
Posts: 9,597
Likes: 1,172
From: San Jose, CA
Yes, and no.
Under most circumstances, ignition issues gets worse as the engine load increases. But there are things that are just bad enough to notice at idle because the engine is more sensitive to certain things that you won’t notice at higher RPM.
That’s why I wanted to mention it, but didn’t want to rule it out.
Under most circumstances, ignition issues gets worse as the engine load increases. But there are things that are just bad enough to notice at idle because the engine is more sensitive to certain things that you won’t notice at higher RPM.
That’s why I wanted to mention it, but didn’t want to rule it out.
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Tuned
Joined: Sep 2024
Posts: 271
Likes: 81
I'd echo vacuum. Vacuum line is cheap and getting those replaced with new line is a wise idea. I had a very similar problem and it was the vac lines off the intake leading to the trans. Looked fine, but once removed you could see cracks. New line solved this for me.
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