340 six pack idles too fast after reinstallation

My divorced choke wasn't working correctly so I had to take it off to adjust it. Unfortunately one of the bolts broke off so I ended up having to remove the carbs to get to that bolt to fix it. Got everything back together. I didn't mess with any adjustments on the carbs because it ran fine before just hard to start due to lack of choke.First crank up and it idles way too high like 3000 RPMs. What did I mess up and how do I fix?

Now that your choke is working, you need to set the "high idle" speed on the fast idle cam. Service manual says:
- Engine off.
- Transmission in Park or Neutral.
- Open throttle slightly.
- Close choke plate until fast idle cam tang can be positioned on the second highest step of the cam.
- Start engine and determine the stabilized speed.
- Bend the fast idle tag with a screwdriver placed in the tag slot to set to the specified speed (M/T 2600 RPM, A/T 2800 according to 71 Ply SM).
- Caution: Bend tag perpendicular to the contact surface of the cam. Bend only when the tang is clear of the cam.
- Stopping the engine between adjustments is not necessary. However, reposition the fast idle tang on the can after each speed adjustment.

The service manual has a good pic of them making the adjustment. If you don't have one, recommend you get a copy of the factory service manual for your car.

Mine is A/T. Guess I’m just not used to the idle being so high but I guess ~3000 rpms is normal??

As soon as you hit gas it will come off full fast idle and will drop to a more normal idle unless you got the choke closed too much.

Did you connect the PCV hose. Vacuum leak can do this.

Personally I would lower it some. 2800 RPM is just what it says in the 71 SM.

A lot depends on how you drive it. I would lower the RPM and just warm the car up more before driving it. There are several settings for the choke system to get it to operate properly. Choke, choke pull-off, choke unloader settings, etc...

I always warm my vehicles up before driving them now, but back in the day, people would just hop in the car and drive it...I have my fast idle set about 1800 RPM on my cars.

Can't get the curb idle below 1500 RPMs. Any ideas or suggestions?

Start back with the mechanical basics during installation, confirm the end carbs are completely closing independent of the linkage, confirm the linkage is installed properly and operates freely, and travel is adjusted properly, are you using an idle solenoid?

You need to see what is keeping the throttle open or causing the high idle.

Check the throttle cable adjustment/transmission kickdown linkage. Is the cable adjusted long enough/linkage not binding and allowing the throttle to close fully? Disconnect them and see if the idle drops. Since you had the carb(s) off, something may not have gone back together properly.

Check to see if the fast idle cam/lever are touching at idle. They should not be touching when engine is warm and choke is fully open (choke plate should be vertical). Next would be the idle solenoid. Disconnect it and see if the idle drops. If the RPM drops, adjust the solenoid. If not, check the base idle screw and see if you can lower the RPM. Check for vacuum leaks.

If none of these things work, check to see if you have manifold vacuum to the vacuum advance at idle (disconnect the hose). If the RPM drops, check the hose connections. You should not have manifold vacuum to the advance unit at idle. If the hoses are connected properly and you still have vacuum to the advance at idle, the throttles are opened too far.

Did you just remove the center carb or all of them?

Take the carb(s) back off and look for anything hanging up the throttle plates (i.e.; throttle plates rubbing on the throttle plate bores in the base, base gaskets hanging into the bores, bent/binding linkage, etc.). If the throttles are open too far, you'll be into the transfer ports in the carbs, not just the idle circuits.

If it idled well before, go back over each thing you touched one at a time...and look carefully for any problems.

Checked the cable and kickdown. No issues there. Fast idle cam/lever not touching at idle warm. Choke fully open. Solenoid works but I have it adjusted to where it never touches. I'll check the other stuff. Ended up having to remove all carbs because certain sections of the fuel lines would not come apart. I will say other than the high idle issue, runs great.

You disassembled everything up top. Regardless how it ran before it just makes sense to me that you would have to readjust the linkage when it was reassembled. Did you try to start/run the car without the linkage connected? That might tell you whether it's simply the linkage adjustment or something else like a vacuum leak.

OK, one or more of your carburetors isn't closing all the way FOR SURE. Never, ever, ever start up a six pack car without the outboard linkage(s) connected or you can blow the motor (front/back carbs can go wide open with no way to close them). Here's what I would do:
1. Turn the center carb idle screw all the way out (lowest possible idle). I assume you've already done this.
2. See if you can force (gently) the center carb closed any further by hand. If yes, then your return spring may be weak and/or hanging up somehow.
3. Inspect carbs for anything that may have moved & now interferes with any of the carburetors returning to fully closed (vacuum hoses, plug wires, etc.)
4. WITH ENGINE OFF, disconnect the outboard linkage & see if that lets the center carb close even further. If yes, then re-adjust linkage, re-connect & THEN start engine to test.

5. While the linkage is disconnected (see 4), manually move each carburetor by hand gently to see if any one of them is hanging up. It is very common to have a carb/intake gasket hang up the throttle blades on six packs. (fyi-always best to move carbs open/closed while tightening them down to prevent this....nudging carbs/gaskets so each carb moves freely before fully tightening bolts)


If none of that works.... report back & we'll think of other possibilities

Readjusted linkage, no difference. It was instinct to disconnect the linkage at idle to see if that was the issue for high idle.

1. done
2. can't
3. will double check
4. did/done
5. never thought of that will have to check

my gut feeling is that issue probably lies with base gaskets. vacuum hoses all hooked up correctly as far as i can tell. got new Holley gaskets for all carbs. unfortunately had to remove all carbs eventhough i tried everything i could to not have to do so. this is the only thing that's really changed as far as materials go. everything was torqued to spec (200 in/lbs) but still just not sure everything is right there. really don't want to have to remove everything again.........

As for base gaskets,only one's I ever use is the O.E.M. tan composition cardboard .The thin black is fine if both manifold surface and carb base are "perfectly" flat but most are not and they will leak.If you have doubts about the carb base,use a strait edge,you may be surprised.

The ones I took off were the black ones. Ones I replaced with were the same style Holley ones with what looked like a metal insert. Never seen the tan ones where do you get those? I thought originals were the thin black ones from Holley with rear stamped on them.

The tan are available from Mopar Performance,that is what you would have had factory installed.

Not trying to start an argument or anything just trying to understand what’s right. Was looking at most recent Roger Gibson catalog and it has:

“NEW! Authentic Holley 340-6 and 440-6 carb base gaskets. Authentic dark color with “REAR” stamped into gasket as originals”

Is this wrong info?? Never seen the tan ones before this is why I ask. They’ve always been dark. The service manual also shows them dark.

I just removed my rear and center carb. The gaskets were tan. I got new one's that are Felpro 60124. They are sort of tan in color. There not as tan as the one's I took off, but I know my gaskets were not oem.

Every time i see a six pak post i go get the

It's not that complicated.

Please post clear - close pictures of the linkage side and the fuel side.

There are many scenarios that will cause your problem and it is probably something simple. Stop wrenching and let's look.

I still have original gaskets in original Chrysler packaging from 1972,packaged in sets of thee including air horn gaskets,never opened,same as picture I posted.

As Dilbert and I previously stated, there are many things that can cause this. Need to go back over everything from square one and check everything carefully. Odds are something is binding or not hooked up properly and since we aren't there, we can't see the issue.

Turn the carbs over and look to see if the throttle blades are closed fully. If not, back out base idle screw to see if throttle plates close. Look for signs of the throttle blades rubbing in the throttle body. Push the throttle shafts side-to-side and feel for play and any binding while opening/closing the throttles.

If the throttle blades are not fully closed, you need to see what is binding (linkage, throttle plates, fast idle cam, etc.) and causing the throttle to hang open.

Then move on to check the carbs as they get installed...

Do the base gaskets show signs of rubbing anywhere? How about on the edges of the throttle bores in the intake?
It doesn't take much...

Then I would reinstall the carbs loosely and open the throttle bores to make sure they move smoothly and are centered in the bores. Tighten the mounting bolts a little at a time to specification and recheck the throttle for any binding. Repeat on the next carb. Reconnect/adjust the carb-to-carb linkage. Is the throttle return spring weak, not returning the throttle to closed position?

Reattach the throttle cable and kickdown linkage, making sure they don't hold the throttle open. Reconnect all the fuel and vacuum lines.

Check the PVC and power brake booster hoses. Maybe one got damaged during carb removal/installation. Also check to PCV valve to see if it is stuck open. Shake it, does it rattle. You're basically looking for anything that would cause a large vacuum leak. Once running, disconnect the brake booster and plug the line to see if the booster is bad.

Did you move/bump the distributor when removing/installing the carbs?

Do you still have points or has the car been updated to electronic ignition? If still points, check the dwell to ensure it has not changed. Reset as necessary. Check the mechanical advance in the distributor. Pop the cap and check to see if the mechanical advance return properly by rotating the distributor rotor and release it. The rotor should "snap back" into it's original position. Repair as needed.

Start the car.

Once warmed up:
Check the base ignition timing. Is there any vacuum going to the vacuum advance while at idle. If there is, the throttle is open too far or the hoses are connected improperly.

Turn car off.

Good luck. Keep us posted...

Yeah, dilbert is right. It's just a vacuum secondary Holley with two sets of secondaries. They do seem overwhelming to many people, but they're actually pretty simple.

Here are some pics of the setup.

Just an observation:
1- Should your choke rod be straight up instead of an angle?
2- Is your Solonoid screw all the way out and normal idle screw all the way out?
3- Normal idle screw should just be touching and then back it out 1 full turn.

Why is the gasket between the body and the base of the middle carb sticking out?

Why is the vacuum line from the T going to the choke pull off? That vacuum line is suppose to go to the center carb. I think you have them on wrong. Or is it the picture that is hiding it?

1 it is when choke is closed
2 Solenoid is not charged when it is, it rises. Screw is out so they never make contact
3 Ironically and accidentally yes it is

I see what you see. Authentic Holley gaskets installed based on how they were made and how the bolt holes lined up.

It's not. If you look closely the vacuum line from the vac advance is ribbed. The other lines are smooth. The line going to the pull off is from the underside of the center carb. The line from the T is going to the inner port on the carb same as the ports on the outer carbs. The outer port on center carb goes to the vac advance. It's just as obscured in the factory service manual. Very hard to tell which line goes where.

At this point is there a way for me to tell whether the carb base gaskets are the reason for the issue without removing them?

Did a little more research. I think the tan ones may have been for the 440 version while the darker thinner version was for the 340s.

Is there a way for me to tell whether the carb base gaskets are the reason for the issue without removing the carbs?

Had a little time this morning. Car seems to run great just can’t get idle down below 1500 or so. Pulled vac hose to advance at idle. No change. Maybe if I retard the initial timing??

From a post above,have you done this with linkage disconnected ?

1. Turn the center carb idle screw all the way out (lowest possible idle). I assume you've already done this.

Yes

That is some good technical support from the collective
I put the popcorn away for the moment.
Nice pics!
SuperPerformance base gaskets are the best
What happened:
The car ran normal before the center and rear carb came off.
Carbs get reinstalled and the idle is high.
Vacuum leaks usually mean poor idle

Start here
Be sure the distributor is not loose-see if it turns - if that's it stop and fix.
Warm up the engine to operating temp
Shut it off
Be sure the idle mixture screws are at least 1 turn out ccw
Disconnect the throttle cable
Remove the rods from the both outboard carbs - relax nothing is going to happen.
Be sure you leave ithe outboards in the closed position
Be sure to secure the rod from interfering with anything.
Be sure to actuate the outboard carb to be sure the throttle blades come to rest
Lock out the choke.
Turn idle adj screw CCW till it has no contact with the throttle blades

Check the float levels -Trickle out the ctr, just below on the outboards

Try starting the car by just turning the key [ btw a properly tuned car would start right up] If it does not run -it should not run - set the idle screw 1 turn in CW. It should start and run. Work backwards to putting everything in it's place.
No go over to the lift off hood playground where a decent version of the six pak tuning guide is and set the carbs up properly.

If it runs away like before: wiggle each outboard throttle blade while it's running.

Report back

Checked for vacuum leaks all around, carb base etc., nothing. Revisited this, readjusted, and curb idle went down to where it was before. Much better.