Hi i got an ford fairlane 500 -57 with an 312 engine that runs great when driving but i have a problem, when the engine gets warm and im standing still with the engine at idle speed it stalls after maybe 5-10 minutes. when its about to stall i can rev the engine but as soon as i get of the throttle it will die, but if i put it in D and drives for maybe 1 min the idle will work again for another 5-10minutes.If the engine dies it not funny to get started again. i can add that when im driving my engine temp is normal but when im standing still it will go up to maybe 200 degrees F. I have tried several things to solve this and dont realy know what to do. I have change sparkplugs and cables, ignition coil, and installed a pertronix ignitor gen 1 and set the ignition timing to 6°. i have changed all gaskets in my edelbrock 600 and adjusted float level. changed fuel filter, adjusted valve lash. i have also mounted a thick "plate" between carb and intake. nothing has helped. anyone got a clue on what to do next ? and one more thing, if i set idle speed to 600rpm it can be 500rpm a few stops later and can also be 7-800rpm maybe its normal ? and sorry for my bad english im form sweden.

Best regards Joel

Joel I have found that a mechanic's vacuum gauge is invaluable for engine and carburetor tuning and diagnostics. At Sea level a stock engine in good condition should pull 18" to 20" steady needle on the dial gauge. Be sure to check for this. Usually 10° to 12° BTDC is optimum static or initial base ignition timing.

Carburetors have several different circuits that work together but also operate independently of each other. The idle circuit particularly is dependent on a strong manifold vacuum signal, as very little outside air moves through the carburetor at idle. So carburetors utilize engine vacuum for precise metering and atomization of the fuel. As the ignition is advanced at idle the manifold vacuum signal is increased. Study the setup and adjustment carefully and take care that the throttle plates are not excessively open at idle. The idle mixture plays a role in off idle and transition carburetor circuits, where a lot of driving takes place.

The reason the Temp goes up when You are stationary is because there is no Coolant circulation.If You take off the Cap (let it cool off first) and watch the coolant at Idle there is no circulation.When You increase Engine RPM you should see the Coolant moving. One way to improve this is to install a smaller Water Pump Pulley. Also a Fan with more Blades such as a 6 Blade or an Electric Fan helps. I have installed Aluminum Rads in both my 56's and the improvement at all Speeds is very apparent..The Idle Speed should remain Constant once set. If its changing as U indicated something is not quite right. Is the Throttle Linkage free to return so that the Idle Speed Screw is in contact with the Carb Throttle Stop? 

  

A 200f temperature is nothing to worry about IF it stabilizes there.  Does it continue to climb after 200 or does it stay at 200?  Your engine is not overheating until coolant is boiling out.  If that is not happening, then it doesn't matter what temperature it is as long as it is stable.

If the stall only occurs at idle, my guess is that your idle mixture is far too rich.  It fowls the plugs at idle but when it is above idle, the mixture is better and cleans the plugs.  If you don't already have the manual for your carburetor, download it from Edelbrock's site.  Read and understand everything about the carb theory and function so you know how to tune it.

As far as your eratic idle speed, make sure all throttle return springs are in good condition and not broken or worn out.  Make sure your throttle linkage is lubricated and operating smoothly.  Make sure that the throttle plates were not binding on the smaller holes in the manifold manifold and that they are not binding on your spacer.  Also make sure that your mechanical and vacuum advance are operating correctly.  Everything else the same, rpm will increase with more timing and decrease with less so if advance weights are sticking or the vacuum advance  is sticking, it can cause your idle to change.


Lawrenceville, GA

Hi, i have checked the vacuum on idle 600rpm av its about 16 when i measure it on the big middle connection on the front of the carb, i have my distributor connected on the left side on the carb and there is no vacuum there on idle is correct? this is the number on my distributor C3AF-12127-U i have checked so it moves and returns good with vacuum. about the temp i have an electrical fan that starts at about 200f so it wont go much higher than that. i had the carb taken apart a few weeks ago and cleaned and new gaskets, i have tried to set up idle screws but they currently sits at 2 turns out at both sides. When setting the ignition the vacuum should be plugged to the distributor, right ? i will check the linkage one more time to make sure its not getting stuck.

I read somewhere that a 600cfm carb is to big for an 312? dont go over 500cfm with stock engine they said, some of them had problem tuning the 600cfm carb but solved the problem with the smaller carb. is this true? 

update i have now tried to adjust the idle screws to maximum vacuum bat cant get it higher then 16 and it goes up and down between 15-16 all the time

The 600cfm Edelbrock carb is definitely not too big for your engine.  The primary throttle bores are considerably smaller than the secondary bores so air velocity at idle and cruise within the carb is expected to be the equivalent of stock or better in that department.  Vacuum leaks on the ECZ-B manifolds are common so make sure the carb and associated spacers are sealing well to the manifold.
 
You don’t say anything about the overall condition of the engine.  If its high mileage and/or the heads were never configured to run on unleaded fuel, then there is the possibility that the valves are not sealing consistently to their seats.  Valve guide wear is also a consideration as well as the valve lash being set on the tight side.  Don't rule out worn rocker arms.  Performing both a cranking compression test and a leak down test is suggested to get a feel for the condition of the rings and cylinder heads.  By ruling out some of the basic mechanicals that could be the root of the problem, you can then concentrate on the carburetor and ignition systems.

Lorena, Texas (South of Waco)

I'm no expert by any means but could it be either a heat soak issue or vapor lock?

Durham Missouri

I chased a similar problem on a friend's Galaxie late last year.  It was very intermittent and drove me nuts.  It finally turned out to be a bad coil wire.  The wires were carbon in the center and burnt on the end that goes into the coil.  The coil was arching just enough to run the car.   The car would stall, run fine for a few miles then stall again. I was pretty embarrassed when it turned out to be something so simple.  Sometimes the simple things can be the hardest to find.

i dont know the condition of the engine the rocker arms looked okay i think. but about the carb is it possible that the engine gets to much fuel and gets flooded with gasoline and therefor dies? because if i let the engine stall its realy hard to get started again. and if i drive away when its about to stall the sparkplugs dry up and works properly again? just a thought i have. and this might be caused from a to big carb. but i will try to get the cranking compression test done tomorrow. and i have no idea on the milage

The results of a compression test and leak down test will give you a good idea of the condition.

Re the idle screws, one test you can do while it is idling well is to screw one all the way in.  The engine should stop running when you do that.  If it does not, then fuel is getting into the engine some other way, resulting in a richer than necessary idle mixture.  Another thing to check for a rich idle mixture is to let it idle until it stops and then pull a couple spark plugs to see if they are gas fouled..

Re your cooling setup, since it doesn't get hotter than 200 degrees, it is ok; there is no problem.  If you will be more comfortable with a cooler temp, then have the fan turn on sooner.


Lawrenceville, GA