Rochester carburetor '76 *bizarre* update

[TJ Hopland]

The EFE is the valve at the end of the right exhaust manifold.   By closing the valve it forced all the exhaust gas through a passage in the intake manifold and into the other head and out.   Idea was it warmed things up faster.   When things warmed up it would open and things would go back to normal flow.

Does this have the electric stopper do dad on the throttle arm that someone mentioned earlier related to AC?  You would see it if its got it.   Its on the drivers side hanging off the front of the carb.  Its got one wire and a plunger like thing that extends to stop the throttle arm from closing all the way when its energized.

If that's not it then sounds like you need a carb guy to have a look.   All that choke linkage stuff may need to be taken apart and cleaned.

[Jon S]

Getting back to the original issue - since it does kick down and only creeps up in RPM when driving, I still believe it is linkage related, but could be a throttle return spring problem.  In addition to spraying the carburetor linkages, also spray the throttle plate shafts to ensure they are gum free.  I do not think this is EFE related.

["Cadillac Kid" Greg Surfas 15364]

Im with Jon.  Since cleaning up the linkage did make an improvement I would continue on with a good carburetor spray on All the linkages on the choke side as well as trying to get to the throttle shafts.  It is possible that ANYTHING else might be wrong, but stick with the simple things first.  By the way I don't believe you mentioned whether you were driving with the AC on, but the idle is correctly set with the AC Compressor in operation.  With it off, you should expect a very slight increase in idle speed.
Greg Surfas

[Jeff Moffo]

Greg
AC. is not on.  What exactly is the throttle shaft?  Don't laugh!
Are the shafts seen from the drivers side near the throttle linkage? And I'm guessing spraying works best before I start the car, correct?

Have you experienced this with your 75?

["Cadillac Kid" Greg Surfas 15364]

Jeff,
The throttle shafts are the "rods" that go through the carburetor base that the butterfly's (throttle valves) screw to.  There are four spots where they go through the base, and you can get to the outsides and the insides with the nozzle of your carburetor cleaner.  Definitely do this with the engine off, and wait for the cleaner to evaporate and the fumes dissipate, since the cleaner is highly inflammable.
Regarding the AC, it is normal to set the final (curb as they call it) idle with the AC on, since most cars operate(d) that way continuously with the Automatic Temperature Control (ATC) keeping the temperature desired in the cab.  I suggest you turn the AC on, leave it on and try your road test again.
Yes, cleaning the carburetor linkage, etc. is a normal part of my routine maintenance.
Greg Surfas

[cadillactim]

Have you considered the electric choke coil could be acting up? Coil is 38 years old, may not be expanding and contracting correctly. Try rotating the coil a little and see if idle remains low.

Tim

[Jeff Moffo]

I figured those were the shafts. Thanks. AC  is not on because r12 is gone and compressor will obviously not work. I never thought that could be the reason the curb idle was a bit higher. Makes a lot of sense seeing the car was in Miami for a considerable time. Nonetheless, it mystifies me as to why the idle comes way down but then eventually creeps up. Funny part also is that it rarely idles low on a hot start.
Choke plate opens all the way, Tim. Seems to take a while. How long should it take to open in about 60 degrees on a cold start?
Thanks guys.

[cadillactim]

Just because the choke plate is open does not mean the coil is okay. If the coil is not expanded enough to hold the plate open with enough "strength," the air being drawn in the air cleaner can push the plate back down just enough to put the linkage on the first step of the fast idle cam while driving. Push on the choke plate and see how stout the coil has it open.

Tim

[Jeff Moffo]

Never knew that.  I will be out in the garage later tonight and make a test of it.  I will also take a look at the idle cam and see what step it ends up on.
Thanks, Tim.  Appreciate your feedback.

[Jeff Moffo]

So out to the garage I went....
Sprayed all linkages on both sides with Gumout Carb cleaner.  Everything seems to operate well.  Choke plate closed with press of accelerator. Car fired up.  Choke plate opened slightly from vacuum break (pull off).  As car began to warm, I kicked down idle once...then about 1 minute later...kicked it down a second time.  Car idled great...a little rough for a few seconds, then fine.  Choke plate was pretty much in open position. Idle speed screw touched the throttle lever.  NOW...here is where the mystery starts.  After the car ran for about 3 minutes at normal idle, I touched the gas and VIOLA! - it crept right up.  So, I took a look and noticed the curb idle screw was now NOT touching the throttle lever.  Seems the throttle plates were not fully closing, but if I pressed the throttle lever forward, I could tell car wanted to return to its slower idle.  Unfortunately, I could not get the lever to touch that idle screw.  I turned off the car.  Waited about one minute, started the car, kicked down the idle and it began to idle normal....but if I touch the throttle, back up the idle comes...

["Cadillac Kid" Greg Surfas 15364]

Jeff,
Can you "tighten" up the throttle return spring a bit?
Greg Surfas

[chrisntam]

Could the fast idle cam have come back into play?  When he kicks it down, it idles normally, until he presses the gas.  Then the fast idle cam drops back down, holding the throttle open a bit?  What keeps the fast idle cam off the throttle linkage once it warms up?

[The Tassie Devil(le)]

Could the actual throttle linkage be stopping the throttle lever from going to full rest.

Do these carbs have the electronic Anti-dieseling solenoid that closes the throttle off completely when the ignition is turned off?

Sounds like there is a bit of a heat-sensitive operating here somewhere.

Bruce.

[Jeff Moffo]

Greg,
How could I tighten the return spring...?
I also believe it has something to do with the throttle AND the idle cam...

[cadillactim]

Did you check the tension the coil spring has on the choke plate as I mentioned earlier? If there is not enough tension the air flow can close the late enough allowing the fast idle cam to engage on one of the steps again.

If your choke coil is kept in place by screws (some are riveted), try this:  Warm the car to operating temperature, make sure choke plate is fully open. Now loosen the screws and rotate the coil so that it puts more pressure on the choke plate. There should be marks on the choke coil housing, I suggest you move it one notch. Now drive the car and see if the idle stays where it should. If it does, let the car set overnight, and check for cold and warm operation of the choke the next day. If everything works, the coil just needed adjusting. If choke opens too soon when cold, but works fine warm, then your choke coil is bad.

Tim

[Jeff Moffo]

Tim,
Attaching picture of choke, etc.  Choke does have the three screws but notice the little bugger has no marking to line up with the notches on the housing. Usually the words rich and lean are there, too. Seems this has been replaced, correct?  Ill get out there later today after work and do what you suggested. I'm turning CCW direction for more tension, right?

[Julien Abrahams]

I am with Greg: seems like the tension from the choke spring is not big enough to keep the linkages and choke valve completely open. Similar to when the car has cooled down somewhat again. Good luck. Please let us know when the problem is fixed. I'm curious .
Julien.

[cadillactim]

Something already doesn't look right with the coil position. Notice the part number on the coil. The top part of that area is usually in line with those notches on the housing (top right of housing). This coil is way to the left of those notches. I do see a small notch in the coil where the "GM" logo is, but that also is too far to the left.

As far as direction of rotating the coil, you want to rotate it so it makes the choke plate open sooner, so just note the location now then take your finger and put slight pressure on the plate to try to close it. Rotate the coil in the direction that forces the plate back open.

But just from looking at the coil position now it doesn't look right.

Tim

[Jeff Moffo]

I thought the same thing while I was tinkering with it yesterday.  I thought I'd see a significant notch (or raised line) on the coil where it lines up with the housing "dots" in order to have a more significant reference point.  NOTHING except that slight cut/notch.  And it looks too turned to the left (CCW). 
When you say put slight pressure on the plate, are you saying to do this with the car running or off?  I would assume off.
I know you said to warm the car first and be sure the plate is open.

I did notice yesterday that while the plate opened, if I touched it while the car was running, there was a good loose movement in the plate - more than an 1/8 of an inch.  Should there be no play at all?

[Jon S]

Jeff -

The first thing I would do (if you haven't already) is scribe the position the choke climatic Control is/was in before moving it richer or leaner so you have the original point of reference.  It "sounds like" a notch leaner will do the trick, but this may change with the seasons .