Very high idle - 440 six barrel

[Righty Tighty]

Hey all, I brought home a 74 Barracuda a couple weeks ago, and she's fitting right in. I'm doing my best to give her a thorough inspection before *officially* getting out on the road, and naturally there have been some bumps along the way.

I got it to start after flushing the gas tank, new lines, new plugs, oil, fuel filter and sending unit sock. As the choke opens, the idle steadily increases until what sounds like about 2500 rpm. I haven't connected the tach to find out exactly what the rpm is. I gave a quick check for vacuum leaks, and then checked the initial timing. Over 25 degrees initial (vacuum advance disconnected and plugged). I bumped the timing down to about 10 advanced so that it was drivable enough to flush and bleed the brake system, but even at 10 it sounds a bit high, like maybe 1500 rpm.

The curb idle screw is about as far out as it will go, idle mixture screws are 2 turns out each. I haven't inspected how much of the transfer slots are exposed, but I can see that the outboard throttle plates don't appear to be sticking open. I haven't looked at the distributor yet. I disconnected the brake booster vacuum line and plugged it, no difference.

Here's what I know about the setup that might be relevant:
440 six bbl, 727, headers, power brakes. PCV port is capped, vacuum advance runs to ported vacuum, from what I can tell the fast idle cam isn't hanging up.

What else can I check for?

 

[Chryco Psycho]

Fast Idle cam is my first thought , there is a small tab under the cam that is bent to allow it to drop completely below the idle screw .
Next would be linkage adjustment so disconnect the links to the outboard carbs & make sure they are fully closing & adjust the rods so they sit confortably in the tabs on the throttle shafts without pulling the carb open or holding the center carb open .

 

[Daves69]

It doesn't have a solenoid that is energized by chance..................

 

[Righty Tighty]

Forgive my ignorance, but I thought the idle cam was the blue plastic piece here. There's no metal tab on that piece to bend, plus there seems to be a broken bit that I've circled in the second picture.

This is how the solenoid sits as is. I'm not sure how it's supposed to be.

 

[Chryco Psycho]

Thats funny , I can see the metal tab in your picture but that does not seem to be the problem as the cam is dropped below where it would hold the idle up .
look at your picture there is a tab to the left of the blue cam you bend that to change how much the cam is lifted with the choke closed .
SO try the linkage , in the second pictures showing the idle solinoid you can see the clip on the linkage to the fron carb , disconnect both of those & see if the idle comes down if so adjust the length of the rods so they sit loose in the end carbs

 

[Righty Tighty]

What is the metal tab you're talking about? I thought the fast idle cam was the blue plastic piece in my picture. There is no metal tab on the blue plastic piece.

 

[Daves69]

The part that's broke off of the fast idle cam is the choke unloader pin. The unloader tab opens the choke at full throttle.
link.........
Chicago Carburetor

Obviously your solenoid is not energized causing the high idle. Settings for these are in the FSM.

You can find FSM here. A '71 manual will surely have the six pack info in it. Not sure about '72-'74.
..........
Service Manuals – MyMopar

What is the metal tab you're talking about?

 

[Righty Tighty]

Thank you SO much!

Believe me, I always try to do my homework and figure things out before asking questions, but sometimes I just run into dead ends.

 

[Chryco Psycho]

You could easily drill the plastic & add a steel pin for the unloader function .
There is an arm under the bottom of the cam , as you close the choke that arm lifts the fast idle cam up , you can bend the arm so the cam comes up higher or less high with the choke fully closed , I can see it in your picture ! The fast idle cam is not the problem though as it is dropping down fully & not affecting the idle speed .

 

[Ron Kirkpatrick]

I just have one in my shop doing same thing. With it. Some gm guy did carbs. Wrong base gasket in front carb. Was holding it slightly open. so I did all 3 carbs. Good as new

 

[Righty Tighty]

You could easily drill the plastic & add a steel pin for the unloader function .
There is an arm under the bottom of the cam , as you close the choke that arm lifts the fast idle cam up , you can bend the arm so the cam comes up higher or less high with the choke fully closed , I can see it in your picture ! The fast idle cam is not the problem though as it is dropping down fully & not affecting the idle speed .

Thanks! I found a new replacement part though, I think I'm just going to go that route.

I just have one in my shop doing same thing. With it. Some gm guy did carbs. Wrong base gasket in front carb. Was holding it slightly open. so I did all 3 carbs. Good as new

I'll be getting after it today to see if I can make any progress. Hopefully I can figure it out without removing the carbs, but if that's what it takes...

 

[Ron Kirkpatrick]

Thanks! I found a new replacement part though, I think I'm just going to go that route.


I'll be getting after it today to see if I can make any progress. Hopefully I can figure it out without removing the carbs, but if that's what it takes...

They are very simple to do.

 

[704406]

If you look closely at the Daves69 picture of the distance between the idle solenoid and the idle screw and then your pictures there is quite a large difference in the distance between the two, they are both not powered in either picture. That tells me something is different between the two setup's
Chryco Psycho is correct in saying disconnect the outboard carbs throttle linkage and see if the centre carb throttle closes more. It might only be one carb's throttle linkage that's not adjusted correctly.
I'd do that before I started pulling the carbs off.

 

[dadeo1852]

Looking closely at Dave's pic versus yours for the throttle blade position on that center carb, you can easily see that your throttle blade is open quite a bit more than Dave's so something is hanging yours up. Like was said, disconnect front and rear carb linkage first to see if this allows throttle plate to close (easiest fix). Something is not allowing it to close. I once had a throttle plate not centered in the bore which wouldn't let it close until I loosened the 2 throttle blade screws and it shifted/centered itself which cured my problem.
Andy

 

[Old Mopar]

there is no simple answer to your situation, As seen posted many times now - smarter folks always tell us the carbs need to be set up properly - there is a lot of detail in that - so instead of chasing your tale like you are now you need to understand the basic of setting up the fuel system. I am not interested to detail to you how to do this but i know there is published information out there to assist you. Beware of what people suggest before you do the fundamental set up.

 

[fastmark]

Old mopar is correct. I’ve been working on six since I bought my first one in 76. One of the reasons I got the car is he could not make the six pack work. They are not hard to fix or adjust but there are a lot of places to fix and adjust. I’ve decided to start a restoration service for six packs and one of the things I plan to do is have a test mule motor to set them up before they ship. There are just some things that are internal that need to be addressed and many adjustments that need to be made before they can be correct. Some metering blocks need to be replaced. After all, they are fifty years old. The one I’m working on right now would not idle properly after driving it hard enough to get into the secondaries. The front carb would not close easily. I had to replace the baseplate. You could have timing issues as well. It does look like your center carb may not be closed enough. Check the transfer slot on the center carb and set it at .040 for starters. Judging by the solenoid, choke pulloff, and H bolts, you could have an original 69 setup. What are your carb numbers? What is your metering plate numbers? Some racers could have drilled the throttle blades bigger as well.

 

[Righty Tighty]

there is no simple answer to your situation, As seen posted many times now - smarter folks always tell us the carbs need to be set up properly - there is a lot of detail in that - so instead of chasing your tale like you are now you need to understand the basic of setting up the fuel system. I am not interested to detail to you how to do this but i know there is published information out there to assist you. Beware of what people suggest before you do the fundamental set up.

Thanks. I'm still pretty new and learning, so I'm trying to take it one step at a time. I just got a book in the mail yesterday on six pack engine building and tuning, looks like it has a lot of good info in there.

Old mopar is correct. I’ve been working on six since I bought my first one in 76. One of the reasons I got the car is he could not make the six pack work. They are not hard to fix or adjust but there are a lot of places to fix and adjust. I’ve decided to start a restoration service for six packs and one of the things I plan to do is have a test mule motor to set them up before they ship. There are just some things that are internal that need to be addressed and many adjustments that need to be made before they can be correct. Some metering blocks need to be replaced. After all, they are fifty years old. The one I’m working on right now would not idle properly after driving it hard enough to get into the secondaries. The front carb would not close easily. I had to replace the baseplate. You could have timing issues as well. It does look like your center carb may not be closed enough. Check the transfer slot on the center carb and set it at .040 for starters. Judging by the solenoid, choke pulloff, and H bolts, you could have an original 69 setup. What are your carb numbers? What is your metering plate numbers? Some racers could have drilled the throttle blades bigger as well.

Thanks for the tips. I have a few days off starting tomorrow, I think I’ll try to address the basics (like transfer slot exposure, etc) and make sure I’m good to go there. I also have yet to actually measure engine vacuum - all I’ve done at this point is check for leaks.

 

[Righty Tighty]

Well, I started looking at the basics, beginning with the float bowls just to make sure I'm starting at square one. The outboards seemed to be adjusted properly, but the primary was bottomed out - empty. After some trial and error, I was able to get it set correctly. Reset the idle mixture screws to 1.5 turns out. I tried to visualize the throttle plates, and from what I could see they all looked closed.

I gave the engine a little more timing advance, initial is now at 15 - seems much happier, although the idle is high. With a vacuum gauge connected to manifold vacuum, I took a reading of 17 mmHg. Couldn't seem to get any effect on vacuum by adjusting the idle mixture screws, so I moved on to the idle speed screw. I tried lowering the RPM by adjusting it, but the engine would slowly sound like it was being choked out at anything below 15-16 mmHg, and then die.

The high RPM issue pretty much only surfaces after the engine is at operating temp, so I'm trying to think of what it could be that changes or opens as the engine warms up. I think today I'm going to look everywhere I can to make sure there's not a vacuum leak.

 

[donny dotson]

A few months ago I built a new 440 and installed a all new 6 pac set up on my Cuda and experienced the same issue. One of the linkage parts on the passenger side of the center carb was a little tweeked from the factory causing a idle to not be ajustable below 1200 RPM.This was a new carb.

 

[Righty Tighty]

I ended up adjusting the outboard linkages to try to make sure the plates were closing all the way, definitely helped a lot. I still need to install a tach, but the engine sounds like about 1200-1500 RPM -- much better than before. Someone on another forum pointed out that the throttle shaft levers are at different angles, and that it probably means one of the plates isn't closing all the way. So, I'm going to disconnect the outboards and have a look.


At least the engine is idling at a survivable enough rate so that I can drive it around the block while tuning. For now, I need to address the brakes so that I don't have 15 year old pads and shoes disintegrating while I'm driving down the road...