As a test, to find out if the pcv valve is causing the high idle, simply disconnect it from the carb and plug the port on the carb.  You won't hurt a thing to run it at idle like that for a test.

I don't know what manifold temperature should be for a good running engine.


Lawrenceville, GA

The PCV Hookup must be Airtight with the only "Air" intake being from Valley Cover. The PCV I have on mine is a Fram FV411. I plugged it in and worked very well with no further Modification. PCV Valve is Sometimes Trial and Error to get One that works for your Installation. It sounds like You have some Adjustments to make to Carb. I would suggest disconnecting and plugging PCV hookup and setup Carb without it. Once U have adjusted properly plug the PCV back in and make Mods so it works without excessive Air passing at Idle. Then You will at least know any Problem is from PCV.

  

will give it a try, restrict air flow on the PVC
Thanks,
Tim
Waiting Room for Heaven, Fl 33706

You have a Thunderbird Cover. That Tube should be removed and PCV plugged directly into Pushrod Cover. Is there a Reason U used it to hookup a PCV?. The PCV  can allow too much Air to pass into Carb at Idle. Trying a PCV from a smaller Engine my help or try restricting the Hose from PCV to Carb. Cut down Airflow. 

  

Charlie,
The tube I'm taking about is the old crankcase tube that sucked the fumes out of the crankcase.
It hung over the back of the engine and the fumes escaped under the car. Drag tube ?
Any how, I opened up the idle circuit screws  to 2.5 turns, hooked up the vacuum gauge and closed the idle screws one turn and got between 19 and 20 inches of vacuum. Also adjusted the throttle screw and the idle is now 650 rpm.
BUT !! the exhaust manifold temp on left is 544 degrees and on the right it is 491 to 480 a big difference and closer for both sides.
What would you day the exhaust temp should be at the cylinder closest to the firewall ?

Some PCV Valves can be installed backwards.  A PCV valve can be thought of as a controlled vacuum leak and since most PCV valves used are not application specific to our engines, it can be too much of a leak for the combo.  The best you can do for an off-the-shelf valve is to use a pcv valve from a similar size and power engine.  There is an adjustable, rebuildable valve on the market but it is more expensive than most seem to want to spend. http://mewagner.com/

However, the way you describe yours, I'm either not understanding or it is installed totally incorrectly.  When you say exhaust tube, do you mean the exhaust pipe?  The valve should be between the crankcase and carburetor


Lawrenceville, GA

Hey Charlie,
About vacuum leaks..........i have a PCV hooked up to the exhaust tube and connected to the back port on the carb. That would be a vacuum leak into the crank case...RIGHT ?
Could the PCV be installed backwards ?  
Tim, Florida

Thanks,
I have a modern electronic distributor and coil to go with the Summit carb.
I'll work on the problems at had and get back to you later on.
Again,
BIG THANKS FROM HOT 'N HUMID TIM IN FLORIDA

I don't know why one bank is hotter.

If the throttle speed adjust screw is backed all the way off and it still idles at 700rpm, then some possibilities are:
The throttle is hanging open, maybe caught on the gasket, maybe stuck in the throttle bores of the intake or spacer.
The secondary throttle is adjusted too far open.
Vacuum port without a cap
Vacuum leak.
Some other means of getting air into the intake.

Since the engine runs with the mixture screws all the way in, you need to fix that.  Anything else will be only a bandaid on the problem, which could lead to far more expensive problems, fuel washing the cylinder walls, oil dilution, etc.

Fix the idle speed problem and idle mixture problem and then move on.  Maybe they are the actual issue, too.

Another thing is that your '56 312 requires a '57 or newer distributor to work with the Summit carburetor.  I don't think that would cause the hot bank issue, though and it would not cause the idle speed and mixture problem.


Lawrenceville, GA

Charlie,
All good info, but, why is only one bank hotter ?
Also, the throttle screw is back as far as it can go, it is not engaged at all.
What if I open the idle screws 2.5 turns to let more fuel flow.
Because it is LEAN, that means it needs more fuel...right ?
Now with the idle screws open, I have to turn the throttle screw in
to prevent the engine from stalling and this gives more fuel
What are you thoughts ?
Tim
Florida