The Stovebolt Site Forums The Shop Area Engine Shop Sporadic stall & won’t restart in hot weather

My ‘49 3600 (216) typically runs well, however, once or twice a year when driving in temperatures above 90° it will unexplainably shudder, and then stall at a red light. It will not restart until it sits with the hood open for about an hour. I do not believe the truck is overheating, I can let it sit and idle in the driveway for 20 minutes on a sunny 92° day, and the gauge never gets above approximately 190. I do notice on the times that it stalls and won’t restart there is fuel leaking from the carburetor at the throttle linkage. Both sides of the carburetor at the throttle linkage linkage are leaking fuel. It happened today, temperature outside was 91° but, again, temperature gage was just slightly above 180°. My Shadetree mechanic brain is out of possible causes. Any ideas? Thanks so much, I love this site and all of your help.

It sounds to me like the needle and seat in your carburetor are not stopping fuel from running in (which is causing extreme flooding). There could be a few different reasons for this. Do you have a Rochester carburetor? Has it been rebuilt recently? Is your engine running very rich (black smoke, black sooty deposit on your spark plugs)?

Put an inline fuel filter between the fuel pump and the carburetor to catch the crud that's coming from your fuel tank and holding the needle valve in the carburetor off its seat. Use a real filter- - - -one that's about 1 1/2 inches in diameter- - - -not one of those clear plastic Mickey Mouse strainers. They're only able to strain out rocks, marbles, and bowling balls!
Jerry

It is a Carter W-1 carb. It does not seem to be running rich, in fact, it runs happiest with the choke pulled out about a half inch or less. Changed plugs last year didn’t notice any black or sooty buildup on the plugs.

Good point on the fuel filter. When I bought the truck, it had a glass bowl fuel filter mounted just before the carburetor. I had trouble with the fuel boiling in the filter, so I removed it, put in a new fuel line and wrapped it with insulation. But never replaced the fuel filter now that you mention it. I have historically used a standard NAPA fuel filter on my 62 Plymouth and never had an issue, is that the type of filter you are referring to. About an inch and a half in diameter. But I’m still left with a question why this only seem to happen in very hot weather?

Did you check for spark after it dies? May not be a carb issue.

It doesn’t seem the weather or your engine is running too hot to me, but if that’s what is happening then maybe your fuel is boiling in your carburetor. Does your carburetor bolt right on to your intake manifold or do you have the insulating spacer? If you don’t have that spacer then you should get one. The spacer is about 3/4 inch thick and made of a hard rubber or a phenolic material.

I will check the spark next time this happens. Honestly, it acts as if it’s not getting any spark, no attempt to fire at all, even with starting fluid. I have heard in the past that coils can fail at high temperature, don’t know if this is true, or not? I have a spacer between the carb and the intake although I just ordered a new spacer I can’t imagine it will make a difference, but I am willing to try about anything right now. I have considered installing a homemade shield around the bottom of the carburetor to deflect some of the heat from the exhaust manifold, but I always get stuck in the idea that it was hot in 1949 and the engineers didn’t seem to think it was necessary. Thanks for your thoughts and if anything comes to mind let me know!

Yes coils can fail at higher temperatures and so can your condenser. Generally those don’t cause the sort of fuel problems you mentioned but never say never. If your coil is attached to your cylinder head try moving it away. Remember to plug the two bolt holes to keep oil from leaking out.

I don't think heat is the main culprit. I drive my '50 216 all the time here in Atlanta and it's hotter here than Detroit.

Carburetors should never leak. Fix that first.

TKM While your waiting the hour,go to Mickey D,s and get a cold drink along with a large cup of ice. Slap a big ole handful of ice on your fuel pump,once it's cool try it. If it was dirt in the fuel don,t you think it would do it more often?? Just something to try. My fuel pump isn,t even there and fuel line has so much pressure it can,t vaporize.

I had the same problem with my 1939 216. At times the engine would just stop, others times it would start missing. Outside temperature in high 80s-90s. Would not restart. Wait awhile with the hood open and it would restart. Changed the coil and no more problems.

Rick G.

Next time it dies, pop the distributor cap loose and watch the points for spark while the engine is turning over by the starter. That is easier to do than removing a spark plug if you don't have any tools with you.

Thanks all, the plan is to replace the coil, easiest 1st move, like the idea of keeping it away from the block –- carb rebuild is next and maybe a bit of a heat shield between exhaust manifold and carb. Will let you know what works. Also going to add a fuel filter just because I should, although That’s probably not the issue since this is strictly a hot weather problem. And like rickmg only when the temps are pushing 90. At even 80° I can drive it all day with no problem.

Hey TKM, I jumped on tonight to do some research on a very similar issue I am having with my 1951 3100 Chevy with a 1957 235 truck engine. A couple weeks ago, after driving the truck for 1 hour, the engine cut out completely while still driving. When we popped the hood, there was fuel leaking out from the carb and the engine would not turn over. In my two years of ownership of this truck, it has never behaved like this. Today, we changed the spark plugs. The old ones were black and sooty. The engine fired up for 15 seconds, and abruptly died. There was still fuel coming out from the carb.

My next step is to replace the ignition coil. After reading this thread, I am also going to check the carb again for debris or a stuck float. The third plan of attack (if the first two don't work) is to look at the distributor more closely. Please let us all know how you fair with the new coil. Best of luck!

This sounds like a problem we used to have back in the day. The fuel in the fuel line gets so hot it forms bubbles, and that kills the engine. Cooling it off fixed the problem every time. Here's what you can do to verify it. Get a can of ether. When the engine dies again, spray the metal fuel line with ether. If it starts right away, you've located the issue. It's usually caused by a fuel line that is too close to the engine. Find a way to route the line farther away from the engine, and the problem with go away forever.

Take a look at your metal fuel line. If any of it is touching or very close to touching the engine, move it away by bending it slightly. Those engines came with standoffs to hold the fuel line away from the head.

Fix the carb problem first before you spend money on ignition parts. Black and sooty plugs means they're getting too much fuel.

All, as always thanks for your replies and thoughts. I already purchased a new coil going to throw that on today. Spark plugs look good. Previously installed a new fuel line from the fuel pump to the carb, kept it away from the engine and wrapped it with insulation. But the design of the engines with the carburetor right above the exhaust manifold always leads me to think the fuel in the carburetor is boiling. Why on this 49 and not others? I don’t know. A couple of thoughts I’m going to pursue are installing a heat shield under the carb and possibly wrapping the exhaust manifold with the type of insulation that hot rodders put on open headers. My German ancestry suggest I won’t give up, lol. But will do all this one step at a time and let you know what happens!

With all due respect (I really do actually mean that), it would be more beneficial to actually test for spark once the engine dies on you the next time. If you simply throw a new coil on it you won't know for certain if your current coil is failing once it is getting hot from internal faults.
Why is this important to the Stovebolt World? We will all eventually find ourselves on the side of the road a long way from home with a similar dire situation. If you were to go through this diagnostic work and come back to us with the result that your coil temporarily conks out
when it gets hot, we will all have that information so that we can confidently rescue ourselves when this happens to us.
A faulty fuel pump, or drifting debris in the gas tank will give you a similar temporary no-start situation, but those are harder to diagnose.
Checking for spark as soon as the engine dies is very easy and definitive.

Thanks Carl, good advice. I’ve changed my plan a little bit. I’m going to start with the fuel system. Installed the new filter just because I should have a fuel filter, don’t expect that to change anything really. Been out of town next move is to rebuild the carb or have it rebuilt. Also thought I would “double insulate” the fuel line, perhaps wrapping with rubber fuel hose, and then wrapping it again with the fiberglass/reflective insulation, some of which I already have in the garage. When adding the fuel filter, I had a little extra “slack“ in the fuel line and was able to keep it a little further away from the engine. If all that doesn’t fix it for sure I would check for spark next time. (Hopefully, after changes to the fuel system, there won’t be a next time) Plan is to be able to pinpoint the cause instead of doing too many things at once. Also, considering carrying a spare coil in the truck, so if it happens again, I can swap out the coil and see if that solves the issue. Thanks again👍🏻

Is this a steel or rubber fuel line?

There is no reason to insulate any fuel lines if they are of original design and routed as originally designed. Vapor lock from hot fuel lines in these trucks is a myth.
If underhood temperatures become hot enough to boil the fuel, you would not be able to put your hand on the fuel lines.
If the underhood temperatures ever do reach those temperatures, you have a much more serious engine problem than what would be caused by a bad coil or a faulty fuel delivery system.
Once again, don't do anything to the truck until it dies again, and then immediately test for spark.
Get back to us after that. We can then move on to the next step.
I am attempting to save you a lot of unnecessary work, as well as prevent you from complicating the diagnostics by throwing parts at the engine.

I’m with Carl.

There are hundreds of trucks represented on this board with a metal fuel line routed in more or less the factory manner. Some might have a short section of rubber making a connection to carb and/or fuel filter. But other than that, many trucks with nearly identical pump-to-carb fuel line routing. Detroit is certainly far from the hottest climate these trucks are driven in. If there were a pervasive design issue for which insulating lines was the cure, nearly all of us would be doing it.

I’m not convinced that spark is the issue, but Carl is correct that it’s the first and easiest thing to test. If you have spark in one of these no start situations, there are several other fuel system tests that could be done first.

That's true. I live in Atlanta and drive my truck all the time for work in 90+ degree weather, in rush hour traffic, stop and go, etc. and have never had a vapor lock, high heat problem. All stock engine, carb, fuel pump, steel lines, etc.

Steel dissipates heat better than rubber anyway. Insulating the lines means that if and when they do get hot, they will stay hot.

Need to better understand definition of terms here. Vapor lock is a commonly discussed issue in the automotive world. Is it possible to have “fuel expansion” that does not rise to the level of “vapor lock?”

Whatever you want to call it, there are conditions which cause some vehicles to have fuel-related hot start issues.

For instance, my 1951 with a 1962 235 typically starts on the first couple of revolutions once warmed up. It’s a very satisfying thing.

But once in a great while, on a very hot day after a short shut down (like a fuel stop), it will turn over and turn over and act like it doesn’t want to start. I have figured out that holding the pedal to the floor corrects this immediately. My theory is that the heat soak from air not moving and coolant not flowing, is causing some sort of fuel expansion that challenges the needle and causing a flooded condition. And that holding the throttle open is clearing that flood.

Is that a viable explanation and if so, what do you call such a condition other than vapor lock?

JW51 I would not term your hot start issue as vapor lock. In your case (and I am sure others) the short shut down heat build in the carburetor is pushing fuel vapor into the air intake system causing the over rich condition that is cleared by increasing the air those fuel vapors are mixing with by opening the throttle.

A true vapor lock condition is created when there is a portion of the fuel delivery system (typically the fuel pump or carburetor) is hot enough that the fuel vaporizes in that location. If it is the fuel pump the pump can not pump vapor because it is compressable, so no fuel is delivered. If it is the carbruetor the fuel vaporizes and is released through the vent system and there is not enough fuel delivered through the metering systems to run the engine. This can also happen in the fuel line, typically between the fuel tank and the pump where the fuel is under vacuum from the pump suction. One of the reasons in tank pumps are used, they only push fuel under pressure, they do not pull fuel creating that vacuum condition.

Do you have a properly functioning heat riser valve on that engine? If not that can contribute to hard starting when hot and other fuel type issues.

Mine works. But that it a great question that the OP should look into. The heat riser is a bigger deal than most people seem to think.

Not sure what/where the heat riser is or what function it performs᠁᠁

Reply to an earlier post, fuel lines are steel.

If you have a stock exhaust manifold, there is a half moon shaped counterweight just below where the four runners become one. Directly opposite, there is a bimetallic spring.

In the middle of all that is a flap that opens to allow exhaust heat to warm the carb, and then the spring closes it once engine is warm.

Find the part and see you can rotate the counterweight. Report back with findings. Also, search old threads here for tons of info on the topic.

Here are some pictures.

Todd

Thanks for your replies and pics, did a little research on my end have a basic understanding of the function of the heat riser. Located it on my ‘49 (hate to admit it, but I never noticed it before) and it moves easily back and forth – tomorrow I will put some heat on with the heat gun and make sure it “opens” as it should. Will update then.

All, finally had a chance today to get back to the project. Started the truck and watched the heat riser and it worked like a champ. Took about 7 to 10 minutes or so and it begin to slowly open and stayed open. I drove it around about seven or 8 miles, was still open –- parked it when it cooled it closed.

Next, I removed the carburetor, going to rebuild it. When I removed it I looked into the intake manifold there was an eighth inch + of fresh fuel lying in the manifold. I don’t profess to be an engine expert, but I’ve rebuilt carburetors on other cars and never noticed fresh fuel lying in the intake manifold. I will keep you posted. I feel like I’m finally chasing the right dog. Your thoughts?

Yes, your carburetor needs to be rebuilt. Make sure you get the correct kit and not a generic kit from Auto Zone or whatever.

Contact www.TheCarburetorShop.com to get the exact kit for your carburetor.

I don't think you ever stated what carburetor you have. If it's a Rochester B, the accelerator pump base is probably warped.

Carter W-1

All,
well, it’s been awhile since I got back to everybody here is the latest. I replaced the carburetor. It seems to have resolved the issues. The old carb was just dumping fuel at a very large rate and in hot weather the symptoms worsened. Also had suspected the coil, but there seems to be no issue there. Sorry for the delay in getting back to all of you. I certainly appreciate your help. Life has intervened in the last year, but now back, enjoying the truck and making progress nonetheless!