Boomer880

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!!!

KenSny

Check throttle linkage. Dry pressing gas pedal (have someone else press pedal), see if is binding or hanging up somewhere.

HeadsU.P.

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?

Fredtoo

Is there a Fast Idle adjustment on the choke that is holing the throttle plates too far open?

Boomer880

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.

HeadsU.P.

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.

Boomer880

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?

HeadsU.P.

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.

derekderek

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.

Boomer880

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.

HeadsU.P.

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.

Boomer880

Let me give this a try!

derekderek

does the choke lock the secondary air valves? or can they open when choke is shut?

Tiger Joe

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.

HeadsU.P.

Boomer,
You never established nor did I ask: what carb is this?

HeadsU.P.

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!

derekderek

the 3 gaskets implies smiley face q-jet setup.

Fredtoo

Not as far open as you think for an engine that has no load on it.

Boomer880

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.

Tiger Joe

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!