Engine redlining at start
Thread Starter
Instructor
Joined: Nov 2018
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From: Chicago
Engine redlining at start
1968 with a 427/390 AT with a newly built Lars carb and using the three gaskets as recommended.
Last week, after having the car sit for a week, I cranked her over and she revved to 5000 RPM. I immediately shut it down, check the linkage, hoses et al. Found nothing and cranked it over and it started as normal. I assumed maybe the throttle had hit the bottom of the air cleaner and hung up. Drove the car throughout the day with several re-starts and had zero issues.
Today, went to start the car after it sat from Saturday, and it again revved to 5000 RPMs. Checked everything out (PVC has a good rattle to it) and tried again. This time she kept revving to 5000 RPM. Quickly shut it down. I checked the four mounting bolts on the Quadra Jet and gave them some added torque. Still, she revved at the start.
Choke is closed, throttle plates open some when it fired up.
Help please!!!
Last week, after having the car sit for a week, I cranked her over and she revved to 5000 RPM. I immediately shut it down, check the linkage, hoses et al. Found nothing and cranked it over and it started as normal. I assumed maybe the throttle had hit the bottom of the air cleaner and hung up. Drove the car throughout the day with several re-starts and had zero issues.
Today, went to start the car after it sat from Saturday, and it again revved to 5000 RPMs. Checked everything out (PVC has a good rattle to it) and tried again. This time she kept revving to 5000 RPM. Quickly shut it down. I checked the four mounting bolts on the Quadra Jet and gave them some added torque. Still, she revved at the start.
Choke is closed, throttle plates open some when it fired up.
Help please!!!
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
You definitely have some binding somewhere. Are you using a "drop-base" air cleaner? Where do the throttle return springs attach at?
What three gaskets? You lost me there.
I take it you are pumping the pedal a few times before starting? Where is the gas pedal BEFORE you turn the Ign key?
What three gaskets? You lost me there.
I take it you are pumping the pedal a few times before starting? Where is the gas pedal BEFORE you turn the Ign key?
Thread Starter
Instructor
Joined: Nov 2018
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From: Chicago
This happened even after I had the air cleaner off and check the throttle was closed. I have two springs on the throttle to make sure it closes.
The stock intake uses a three gasket set up, which Lars recommends.
The stock intake uses a three gasket set up, which Lars recommends.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
You can not achieve the RPMs you mentioned unless a throttle blade is open, a lot. Either primary or secondary is more than "cracked open", its almost full throttle.
I have seen the carb base gasket catch on one of the four throttle butterflies and hold it open. And that was a A-1 top notch gasket, but just a smidge too small for the carb throttle plates.
Nothing that an Exacto knife couldn't fix in about two minutes flat.
I have seen the carb base gasket catch on one of the four throttle butterflies and hold it open. And that was a A-1 top notch gasket, but just a smidge too small for the carb throttle plates.
Nothing that an Exacto knife couldn't fix in about two minutes flat.
Last edited by HeadsU.P.; Jul 8, 2019 at 07:20 PM.
Thread Starter
Instructor
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From: Chicago
Sounds like I need to pull the carb off and take a look to see what is happening at the gasket level???
So odd, as the car was running just fine. My other thought is that I did not torque the mounting bolts enough, and thus created a gasket failure and a massive vacuum leak. Thoughts on this?
So odd, as the car was running just fine. My other thought is that I did not torque the mounting bolts enough, and thus created a gasket failure and a massive vacuum leak. Thoughts on this?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
I think your first step is to disconnect the gas pedal cable. This will isolate that, as a potential problem. Then, disconnect the throttle return spring at either end.
Using a flashlight, peer down into the carb at full throttle. See if some gasket fiber is too close to a throttle plate. Let go of the throttle. It should SNAP right back even w/o the return springs.
And, maybe you torqued the carb mounting bolts too tight. Causing them to squish some place where they should not be squished.
Using a flashlight, peer down into the carb at full throttle. See if some gasket fiber is too close to a throttle plate. Let go of the throttle. It should SNAP right back even w/o the return springs.
And, maybe you torqued the carb mounting bolts too tight. Causing them to squish some place where they should not be squished.
Last edited by HeadsU.P.; Jul 8, 2019 at 08:44 PM.
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when cold press gas pedal once. then remove air filter and see where choke and throttle plates and secondary plates ended up. then have somebody start it while you are watching the carb. ready of course to shut it right off.
Last edited by derekderek; Jul 8, 2019 at 07:49 PM.
Thread Starter
Instructor
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From: Chicago
The choke snaps shut nicely when I pump it once when cold. I have checked this several times when I received it from Lars.
I looked down the primaries and secondaries and all were in their correct spot. Once I moved the throttle by hand, the primaries moved as I believe they should. I could not see any gasket 'interferance' inside the carb.
I looked down the primaries and secondaries and all were in their correct spot. Once I moved the throttle by hand, the primaries moved as I believe they should. I could not see any gasket 'interferance' inside the carb.
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
No, I mean do both throttle shafts SNAP shut without any return springs or gas pedal cable hooked up? This is not a choke issue. No choke or fast idle is going to give you 5,000 RPMs. You have a throttle binding issue somewhere. One of the throttle shafts is being held open, briefly.
You may work the throttle 20 times in a row and it works fine. Then that 21st time it sticks. I think that's what's going on here.
You may work the throttle 20 times in a row and it works fine. Then that 21st time it sticks. I think that's what's going on here.
Drifting
Joined: Nov 2016
Posts: 1,956
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From: Pittsburgh PA
I had this happen on my 327 once. I have no idea how but somehow my secondaries stuck open a bit. Everything on my car is correct- drop base air cleaner, 3 gaskets, etc.
was exactly like you described. I was driving car it was fine. Shut it off came out next morning and it revved to the moon.
was exactly like you described. I was driving car it was fine. Shut it off came out next morning and it revved to the moon.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
I had this happen on my 327 once. I have no idea how but somehow my secondaries stuck open a bit. Everything on my car is correct- drop base air cleaner, 3 gaskets, etc.
was exactly like you described. I was driving car it was fine. Shut it off came out next morning and it revved to the moon.
was exactly like you described. I was driving car it was fine. Shut it off came out next morning and it revved to the moon.
There is not a amusement park ride in the world that is as scary as a stuck throttle!
Pro
Joined: Jun 2014
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From: New Jersey
You can not achieve the RPMs you mentioned unless a throttle blade is open, a lot. Either primary or secondary is more than "cracked open", its almost full throttle.
I have seen the carb base gasket catch on one of the four throttle butterflies and hold it open. And that was a A-1 top notch gasket, but just a smidge too small for the carb throttle plates.
Nothing that an Exacto knife couldn't fix in about two minutes flat.
I have seen the carb base gasket catch on one of the four throttle butterflies and hold it open. And that was a A-1 top notch gasket, but just a smidge too small for the carb throttle plates.
Nothing that an Exacto knife couldn't fix in about two minutes flat.
Thread Starter
Instructor
Joined: Nov 2018
Posts: 193
Likes: 70
From: Chicago
The carb is a Quadrajet 7028210, which is or a 1968 Camaro or Chevelle. The original carb is a 702816, which is a one year one car carb, so this one made the cut. Yes, it is the original intake with the smiley face design, thus the three gaskets.
To answer the other above question, the secondaries are locked out as designed when cold.
To answer the other above question, the secondaries are locked out as designed when cold.
Last edited by Boomer880; Jul 8, 2019 at 09:36 PM.
Drifting
Joined: Nov 2016
Posts: 1,956
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From: Pittsburgh PA
I had this happen on a Holley D.P. I had removed the air cleaner for a short test run. Forgot about the air cleaner gasket. At full throttle the secondaries sucked the gasket in and stuck. Drove it back home, idling at 3 grand.
There is not a amusement park ride in the world that is as scary as a stuck throttle!
There is not a amusement park ride in the world that is as scary as a stuck throttle!
oh heck ya. like I said mine somehow stuck after I shut the car down ( I had been working on the vacuum system the night before) I decided to take the car to work, so there I am 6:15 in the morning half asleep, and the car immediately starts revving to the moon. talk about a wake up call!