Can outside temp cause a carb’d vehicle to stall?

I drove my old Jeep last weekend all over town. Temps were in the high 80s. Even took it on date night Sat night.
 

I went out of town for work Mon, got back today and took the Jeep to run errands. It ran to the first errand fine, it sat for around 20 mins, and then everywhere else I tried to go it would stall when the idle got too low. I put in fresh ethanol free gas and it ran betterish.  But still stalled.

Now the only other thing I can think of that has changed from last weekend to today is that it is 96 degrees outside with 55% humidity so it actually feels like 102 degrees. Could that be causing the issue? 
 

And the temp gauge on the Jeep never got high, it ran in the range it normally runs. 
 

Any help would be appreciated. 

Sure.  Vapor lock comes to mind.  Any chance your fuel line gets close to your exhaust?

My truck carb will ice up when the weather gets cold before the engine gets to operating temp, but that's kind of opposite of the trouble you're having. 

Edit:  https://help.summitracing.com/app/answers/detail/a_id/5242/~/what-is-vapor-lock%3F

Yup. Especially if your cooling system isn't up to the task.

One thing that can help with the vapor lock issue mentioned above is a carb spacer designed to insulate

I'll check on the fuel line and see if it goes next to the exhaust. I can tell you the fuel line exits the tank straight underneath the Jeep and then runs parallel along the bottom close to the road until it gets to the engine where it turns and heads to the carb. 

any chance the idle jet has some dirt in it ?

Also, I thought vapor lock was when it ran fine and then wouldn't restart until after it had cooled off. This will restart first crank and run fine if you give it gas, but as soon as you put in the clutch and push the brake then the rpm slows and it stalls. Restarts first crank

Like the others vapor lock comes to mind.  Plus . . . 

How long had the car been sitting unused?

californiamilleghia said:

any chance the idle jet has some dirt in it ?

I saw that as a potential problem, and also the idle speed scew may need adjusted. 

L5wolvesf said:

Like the others vapor lock comes to mind.  Plus . . . 

How long had the car been sitting unused?

 

I don't know prior to me getting it. I got it experienced a similar issue on a hot day. GRM helped me ID the carb and a missing vacuum line, and everything was fine. I put the Jeep down for a 2.5 weeks while we roller painted it, but we finished that last week. I drove it last Fri/Sat/Sun without issue. Fri I drove around all over town almost 2 hours in total, and it was fine. Sat was off and on with runs to the hardware store and to help a friend followed by date night that evening with a 30 min drive, sat for a couple hours, and 30 more mins. home. Sun was a run to the store. 
 

Today was start and drive 5-7 miles with stop signs and stop lights with no issue to the first stop. Then it started stalling

PS my wife said the Jeep was mad at me for being gone all week, just like my kids. 

I will add this as an old-school hot rodder.  Vapor lock is incredibly rare.  It was a thing in the 40s and 50s, but the chances you're getting vapor lock are slim to none.  Even if you did have vapor lock, it would present as not running at all, and then going away 15 seconds after you got it started.  Ethanol won't change anything

Is the choke fully opening?

The whole point of a carb is that it moves a mass of gasoline proportional to the amount of air being sucked through it.  Cold air means more air, hot means less... but carbs can only compensate within a relatively narrow range... hence why you have a choke for when it's cold.  It's possible that you're just outside the range of how much it can compensate for hot air and it's running rich.

Popping back through the carb and a "waahh" sound when opening the throttle are indicators of lean.  Black smoke and sputtering are signs of rich.

In reply to Curtis73 (Forum Supporter) :

It's a Rochester 2 brl carb with an electronic choke. I checked that it wa moving but never took a measurement. 
 

I don't understand why it would run fine for 3 days and 4 days later wants to stall and die. It's frustrating when all I wanted to do was drive and bounce around in the Jeep before I had to go into dad/husband mode when everyone else gets home from school. Riding in a 70yo Jeep is an amazing stress reliever 

My Power Wagon used to do stuff like this when it was carbed. It would run perfectly fine, and then wouldn't start. In my case, it ended up being fuel issues. I thought it was getting enough fuel to the carb, but little did I know that there was junk in my fuel tank (mainly debris from an old fuel sender sock that had broken up) that was jamming up the works. I realized that the previous owner had put the inline filter AFTER the fuel pump, so the fuel looked clean in the filter but after putting a clear filter on, I noticed less fuel was getting through. The debris was jamming up the pump and killing them. Once I switched filter locations to before the pump, I saw all the chunks getting captured, and that problem went away. 

Some people still badmouth EFI systems, but you never hear about vapor lock, dieseling, not running well at high altitude, jets getting clogged, etc. Oh, and it's always really easy to tell if there's a classic car ahead of  you on the road (like 1/4 mile ahead) because you can smell raw fuel. I feel better now.

In reply to kb58 :

Nobody knows how to adjust a carb anymore.  Heck, it's taken me a lot of trial and error to get it where I don't smell the gas wafting back through the windows/vents.

Now it's no worse than standing behind the Miata.

I would think that modern low-volatility fuels (especially summer blend) would be less prone to vapor lock than older formulations.

Vapor lock generally will not allow you to restart until the vehicle has cooled off enough for the fuel to stop boiling in the fuel line or fuel pump.  Was it doing this?

I'd look to the stupid simple.  Does it have a fresh vacuum leak, like a split PCV hose or something?

kb58 said:

Some people still badmouth EFI systems, but you never hear about vapor lock, dieseling, not running well at high altitude, jets getting clogged, etc. Oh, and it's always really easy to tell if there's a classic car ahead of  you on the road (like 1/4 mile ahead) because you can smell raw fuel. I feel better now.

My fuel injected RX-7 vapor locks   Fuel pumps are external and on the other side of the rearend from the fuel tank, so the pump inlet has to go up and over.

When it vapor locks, it will not flow fuel for a half hour or so.

Temp now says 95 feels like 101. Jeep has been sitting since my last post. I just hopped back in. Started first crank. Idle looks to be low. Everything I read said it should be at 800 it's at 5-600 when you crank it. I just drove it on a short drive and the idle drops to less than 400. Then it dies 

In reply to octavious :

Carb needs adjustment?

In reply to octavious :

I'll reset the carb when it does that, initial baseline set up.

I'll also squirt starting fluid at places where a vacuum leak might occur.

I want to say I reset it when summer got here, but can't remember for sure.

Did you replace both fuel filters? The inline one and the one in the fuel inlet?

What did they look like?

Pondering this, I wonder if the choke was not coming off all the way before.

Or if the idle was adjusted with a vacuum leak (I see mention of a missing hose...) and now it's too low now that the leak is fixed.

Or if something else had been causing the throttle to hang open like an A/C idle up, or if it uses an anti Dieseling solenoid that now is nonfunctional.  Those are on when the key is on, off when key is off, to shut the throttle all the way when you turn the key off so it won't run on like Uncle Buck.

Ugh. This is one of those moments when I wish I knew more about carbs.  I also wish I could find someone near me to help. I've posted on the local Jeep FB groups about a carb expert willing to help, but haven't found anyone yet. 

Or a loose bolt on the distributor hold down causing it to retard timing?

Carbs can ice up even in hot weather, if the humidity is high.

It's rare but it happens. It's due to the pressure drop in the venturi.

I've seen a ACVW Solex idling with frost on it in my shop in the middle of summer.