Engine stalls and won't restart till it cools down

[signorc 31]

Hello everyone,

I can drive the 302 for hours on highways with no issue at all....but as soon as I get off the highway she'll stall.

She'll also stall  if I take her for a ride up a few hills and engine temp goes up quick.

Once it stalls she won't start back up till engine cools off (about 30 min).

I tried swapping the coil to a new one as soon as it happens but no luck. Timing was also checked and is ok.

Here are the results of each cylinder done wet & dry.   Also, 1 & 8 have a little oil on the spark plugs.

Cydr  dry     wet
1       125     140
2       117     135
3       117     135
4       105     117
5       120     140
6       125     148
7       120     133
8       122     140

302 engine not rebuilt. Still original intake manifold with original Autolite 2100 carb which I rebuilt.

Any ideas are very much appreciated.

 

[69RavenConv 286]

That's a tough one to diagnose on the internet. No starts are usually fuel or spark problems (the holy trinity is fuel, spark and compression, and since the car runs, compression is probably ok). My first thought would be fuel. Are the floats and choke working properly? Carburetor bowl boiling dry when hot? Good spark plugs and wires?

[unilec 57]

Sounds like the carb is getting to hot, so try a phenolic carb spacer and see if that helps. 

 

[1969_Mach1 333]

Are the stock points ignition still being used?  Have you checked for spark at a spark plug during the time it will not start?  That's the very first thing to do to narrow the problem down to spark or fuel.  If there is spark at the spark plugs and the motor will not start I guess it could be vapor lock like unilec is thinking and a phenolic spacer might help.  That is not common for Autolite carbs.  How hot is the motor running?  Fuel line between the pump and carb getting too hot can also cause vapor lock.  Are the carb idle air-fuel mixture screws adjusted correctly?  

[barnett468 418]

Under exactly what conditions does it stall?

Exactly what carb do you have?

How long has it been doing this?

Are you in Italy?

 

[signorc 31]

I have an MSD ignition installed.

The fuel line from pump to carb is covered and sealed with a rubber hose so it can't be that.

Once, when it stalled, I opened the carb to see if the fuel bowl was dry or boiling and it wasn't.....so it's not vapor lock.

the choke works properly.

the engine isn't getting ridiculously hot when it stalls....as a matter of fact the antifreeze doenst even boil into the overflow bowl.

before installing a phenolic spacer (which will give me clearance issues with the hood) I'd like to understand if the stalling is due to a carb or spark issue.

I guess I'll have to try with new spark plugs and adjusting the idle air-fuel screws.

it's been doing this since I bought the car in 2001. 

yes, I live in Italy :)

 

[signorc 31]

I'll get it to stall tomorrow and then check if all spark plugs spark :)

[1969_Mach1 333]

What type of MSD ignition do you have?  First thing to determine is if there is spark when it will not start.  If you find no spark at the plugs then also check for spark coming out of the coil.  A spark tester makes it a little easier.  I use one like this for high output electronic ignitions.  But there are many others. https://www.tooltopia.com/otc-tools-6589.aspx?utm_source=bing&utm_medium=cpc&utm_campaign=PLA&scid=scbplpOTC6589&sc_intid=OTC6589 

If there is no spark anywhere and you have one of MSD's CD type ignition systems (not the ready to run distributor)  here is a simple test to determine if it's the magnetic pickup in the distributor or the ignition box. https://www.holley.com/support/troubleshooting_techniques/

[barnett468 418]

7 hours ago, signorc said:

I have an MSD ignition installed.

The fuel line from pump to carb is covered and sealed with a rubber hose so it can't be that.

Once, when it stalled, I opened the carb to see if the fuel bowl was dry or boiling and it wasn't.....so it's not vapor lock.

the choke works properly.

the engine isn't getting ridiculously hot when it stalls....as a matter of fact the antifreeze doenst even boil into the overflow bowl.

before installing a phenolic spacer (which will give me clearance issues with the hood) I'd like to understand if the stalling is due to a carb or spark issue.

I guess I'll have to try with new spark plugs and adjusting the idle air-fuel screws.

it's been doing this since I bought the car in 2001. 

yes, I live in Italy :)

 

you didn't answer my first 2 questions so i can't help you.

[signorc 31]

Sorry Barnett468,

I answered so many questions that I forgot to answer your first 2 :(

The carb is a rebuilt original Autolite 2100 2bbl.

It stalls in 3 scenarios:

1.  idling for about 45 min

2. After having pushed the engine up hills (for about 10 min) and temp increases

3.  As soon as I get off the highway after having driven it at high speeds for many hours

I rarely drive it in cold weather, so all the above scenarios hold true for spring, summer & fall temps

Thanks for any input :)

[1969_Mach1 333]

Have you checked for spark at the spark plugs when it will not start????  We can play 20 questions, but again, that is the first thing to do.  Then you will know which path to pursue, ignition or fuel.

[signorc 31]

So here's the update :)

Adjusted the 2 idle screws to 3 turns out....and  now idles beautifully.

Checked that the MSD 6AL works properly and it does.

Got the engine to stall by itself after 45 min of idling.  Checked for a spark.  None to be found till I changed the coil to a new one and it starts right up.

So I'm assuming the issue is the coil.  Why would it stop functioning properly?

[signorc 31]

Also, I looked at all 8 spark plugs and they were all white..... so she's running a bit lean.  I turned the idle screws out 3 full turns.

Would having the engine running lean have an issue with the coil?

[signorc 31]

Update.... once i turn the engine off after having replaced the coil, it doesn't start up :(

the msd 6al box is very hot (dont know if it foes normally).

[1969_Mach1 333]

When you have no spark, follow these instructions from MSD.  https://www.holley.com/support/troubleshooting_techniques/   Doing so will determine if it's the MSD 6AL ignition box or the magnetic pick-up inside the MSD distributor.  It might have been coincidence that after you installed a new coil the defective part cooled enough to work again.  I had the magnetic pick-up coil inside my MSD distributor go bad.  Fortunately, my car was still in my driveway.

Adjusting the A/F mixture screws will only affect the fuel mixture at idle.  At high speed, the main jet size needs to be increased.  I've heard Holley main jets interchange with Autolite but I have never tried it so I am not certain.  MSD ignition does a good job of keeping the spark plugs clean.  The mixture has to be fairly rich to start seeing any color on the spark plugs.  All in all, too lean would not contribute to a no spark condition.  Focus on figuring out if its the MSD 6AL box or the magnetic pick-up inside the distributor causing no spark when hot.

Last I would ask if the original wire to the original ignition coil is being used to power the MSD 6AL box?  It should not be because it has a resister wire in the circuit so less than 12V will be supplied.  Some get away with using it and some have had odd intermittent issues when using it.

[Cantedvalve 128]

I am guessing that replacing the coil wasn't actually what made it start, rather the cool down that was allowed to happen.  I've seen many MSD boxes fail this way... which is why I don't run them anymore.  From my experience, they tend to overheat before they fail.

My suggestion would be to ditch the MSD system as a diagnostic step.  if you have a points distributor, put that in and see if it runs longer.

[signorc 31]

Hello everyone, after having adjusted the idle screws, the car still stalled after 45 minutes.

I removed the msd 6AL as cantedvalve suggested, and the car would not stall :) even after 90 min of idling!! Yeah!!!!

Tomorrow I'll push her a bit and see how she acts.

I did test the spark on the plugs after the 90 min of idling and it was a weak yellow/orange spark.  I was dissapointed not to see a nice solid blueish color spark.

Any ideas are appreciated!!!

[1969_Mach1 333]

I've always thought it was either the MSD box or the magnetic pick-up in the distributor.  You should have checked your MSD per the instructions in the link.  It only takes a small jumper wire and you can determine if its the box or the magnetic pick-up when you have no spark.  Magnetic pick-ups are inexpensive.  If its the box, maybe think of switching to something else from another brand or from MSD.  I've hear the MSD quality has suffered since moving manufacturing overseas like everybody else is doing.  I use the 6ALN box.  It's simply because it's the Nascar version of the 6AL.  It's a little larger than the 6AL.  But the electronics in the 6ALN are doubled potted to help prevent components from coming loose from the circuit board and to further waterproof the electronics.  It also has waterproof electrical connectors, but, I think most of them do.

I wouldn't consider Pertronix, stick with points instead.

[signorc 31]

Hello everyone,

take a look at what the inside of the distributor looked like!!!  I guess now I know why I was getting no spark or at best a very weak spark.  Just ordered new set of male spark plugs to install the original autolite female distributor. cap...... but living in Italy it'll take 2 weeks for the stuff to get here :(

 

 

 

 

[barnett468 418]

hopefully that will fix it.