Engine cuts out when warm

[fitter]

Have a stock 69 mustang 428 cj 4 spd.  Runs fine cold. After about 10 minutes of operating temp engine dies out under load . Will stop running. After a minute or 2 will usually start and limp home. So far i have changed fuel pump. Carb 735 holley. Distributor, fuel filters. ,pulled sump from tank replaced screen. Blew gas line out , changed coil ,  kind of at loss now. Anyone have suggestions? Thx

[GerryP]

Points ignition?  Change the condenser.

[Gaugster]

Sounds electrical like the ignition components. Check if anything like the condenser has a small crack and goes intermittent or open with heat and vibration. Any potential leaks in the vacuum advance? etc... that lean it out and bring about vapor lock?

Does it pop when it dies?

[fitter]

Stock dist with pertronix.  Pulled dist out today and swapped another stock unit with Mallory unililite module. Same symptoms. After about 10minutes if you get on it by end of of second gear just falls flat.

[Gaugster]

What's your exhaust setup? Any chance your muffler collapsed? If fuel supply is good you've got me stumped.

[67xr7cat]

Sounds like is running out of fuel.  When it stalls out, leave the engine off, take the filter off the carb. and open the throttle fast while looking down the venturi. You are looking to see if the accelerator pump squirts fuel. If the carb is empty it will be little to none.  A non vented or bad fuel cap will cause this. You build up a vacuum in the tank and lines.

[fitter]

The air filter hasn’t been on in months as I’ve been chasing the problem.  When I move throttle it pumps gas ,  just seems to run out of gas When accelerating , One thing I noticed is wet black moisture out tail pipes when idling.

[fitter]

Exhaust is 2.5 inch mandrel bent.

[jayb]

My guess is that you are boiling the fuel in the float bowls, and it is spitting out of the float bowls and flooding the engine when it warms up.  Seen this a few times before.  Boiling point on today's gasoline is really low.  For a test, you can empty the tank and put in 5 gallons of race gas, which is leaded and will have a much higher boiling point.  If that solves the problem, you need to start thinking about a return style fuel system, and insulating the carb from heat, and the fuel lines from heat.

[Joe-JDC]

Fuel/gasoline cap vented?  Vent line pinched/stopped up?  Rubber swells with the current fuel, and some fuel lines close off.  Change all the short pieces of fuel line in the system with alcohol resistant hose.  Joe-JDC

[Dryhoze1]

My guess is that you are boiling the fuel in the float bowls, and it is spitting out of the float bowls and flooding the engine when it warms up.  Seen this a few times before.  Boiling point on today's gasoline is really low.  For a test, you can empty the tank and put in 5 gallons of race gas, which is leaded and will have a much higher boiling point.  If that solves the problem, you need to start thinking about a return style fuel system, and insulating the carb from heat, and the fuel lines from heat.

X2. Had same issue years ago.
Spot on ..

[Gregwill16]

Have you tried a different coil?

[cjshaker]

Have you tried a different coil?

That was my first thought. I've had this happen a couple of times, with the exact same symptoms. Also, the Pertronix could be acting up under heat, but you mentioned trying a different distributor?

If that's not it, and you have to start looking at a fuel boiling issue, I'd ask if your exhaust crossover is blocked? If not, that would be a good place to start to help control the heat. What are your local daytime temperatures like? A quicker test may be to just try driving the car at night (assuming cooler temps). That could help narrow down if it's a heat problem.

[My427stang]

First question I have is, did it ever run well for you or is this a new build/new car?

If it just started doing it, what changed recently, gas station?  new gas cap? hot weather? just broken in started driving hard?

[shady]

Valve lash too tight?