[69f bird]

I took my '69 Firebird out last week, for the first time this year. It has a 462, 6x4 heads, stock 69 intake and q-jet. The q-jet was professionally rebuilt two years ago, and at that time it got a new gas tank, 3/8" stainless fuel lines, and new fuel pump. It was hot out, around 90 degrees. I had zero problems with it last year, even in extreme heat.

The car started up fine. After it warmed up a bit, I drove about 5 miles, it was running fine, but then it just stalled. Definitely seemed fuel related. It would not restart initially. After trying to start it for about 30-40 minutes, it finally started, thus making me think it is heat related. I drove straight home, only to stall again about 1/2 mile from my house. This time it took over an hour for it to restart. I drove it the last 1/2 mile and in my driveway it stalled again before I got into my garage. Same 1 hour wait for it to restart. I did remove the fuel filter from the q-jet, thinking maybe it was clogged. No difference.

Fuel was 93 octane premium from last fall, treated with Sta-Bil. I do not remember, but it may have been fuel with ethanol.

Any ideas? I have a vented gas cap, and checked it, and it is fine. All I can think is that the new rubber lines, one near the tank and one near the fuel pump, may have been damaged by the ethanol. Or possibly the fuel pump.

Before I begin changing things, any suggestions or ideas? Any help would be appreciated! Thanks!

[4dblnkldude]

Did it run hot before it stalling? When you tried starting it, did it crank at all or real slow?

[shaker455]

Make sure you have spark during you next shut down.
Boiling point of gas is 190 degrees so stay away from 190 degrees.
There is more ethanol in the gas from last year
I'm seeing more damage to carbs from aggressive stabilizers than the fuel itself.
Rebuilds can be every year now.

[Schurkey]

WHAT IS THE FUEL PRESSURE WHEN IT STALLS?

You really have no idea that this is fuel-related. You're guessing. MAYBE you're guessing correctly. This could just as easily be an overheated ignition system, or an overheated intake manifold boiling the fuel in the carb.

[RAFO9A]

I went through an ordeal like this about 2 months ago with my '68 Firebird. My fuel line had rotted and had clogged my fuel filter and carb (Street Demon 625). I replaced the line with Earl's vapor guard fuel line, got a new fuel filter and disassembled the carb and cleaned the fuel bowl, jets, air bleed orifices, accelerator pump and metering rods seats. I also had a worn air horn gasket, which was leaning out the carb. Replaced that too.

After all of that, I was still having issues with the engine leaning out and stalling when hot. So I checked the ignition and found two issues: a hole in my distributor's vacuum advance tube and a worn out distributor cap. Replaced the vacuum line and got a new cap...and that took care of my issues.

I know it's a long reply, but the point is that your issues may not necessarily be just fuel related. It's either fuel, ignition or a vacuum leak.

Sent from my SM-G986U1 using Tapatalk

[25stevem]

After confirming spark then next time it stalls out, and you rebuilt the system and then had no problems last season I would be looking for loose hose clamps due to shrinkage of the hose on the suction side of the pump.

Any mechanical pump finds it much easier to suck air then much heavier fuel, and all too many times there is no sign of a darn fuel leak either!

All it takes is for the hose to have enough freedom to spin a little on the steel nipple and your done, and of course just because you used new hose does not mean that in one years time it could have dry rotted and split in a small area like around a bend.

Look very close for these potential issues!

[78w72]

hard to diagnose these things over the internet, probably best to do some more testing of the basic systems including ignition, ive had modules & coils act weird related to heat or when they are about to die.

but i dont think its a heat related issue for the fuel or ethanol, mainly because you said it was only driven for 5 minutes before it died, that is not long enough to fully heat the engine or intake or carb to boil fuel. new fuel lines are ethanol resistant so its unlikely they are damaged from fuel.

also, there is no more ethanol in todays fuel vs last years fuel unless you are using the 15% option most stations offer now, but its only an option they all still offer standard 10% & many states still have straight gas. but even if its the 15% i doubt thats the problem after a first drive for 5 minutes related to heat or rubber lines.

there can be lose hose clamps allowing air to be sucked in but unless its excessive that usually wont cause the engine to completely die then not retsart for an hour... nothing changes in that hour related to a lose hose clamp that will then magically restart after an hour.

[Jim Moshier]

[QUOTE=25stevem;6363384]After confirming spark then next time it stalls out, and you rebuilt the system and then had no problems last season I would be looking for loose hose clamps due to shrinkage of the hose on the suction side of the pump.

Any mechanical pump finds it much easier to suck air then much heavier fuel, and all too many times there is no sign of a darn fuel leak either!

I concur on this ....spark, fuel delivery are where i would start.

[dataway]

Point and coil ignition or something else?

[hgiv]

A bad coil will do exactly what you described. Starts fine. Heats up and dies. Then it cools down and it starts again. Usually you checked 9 other things while it slowly cools then like magic it works again.

[25stevem]

If your running a factory points type Dizzy and still using points then the wire feeding the points that runs under the breaker plate has been known to dry rot of its insulation to loose enough of it to either intermittently short out or completely short out the points, and then you have no spark.

I had this take place on 389 points Dizzy 35 years ago in a intermittent way.
It took me 2 days to figure it out when 5 second test with a ohm meter would have told me what the story was.

[AG]

Check the basics, fuel/air/spark.

[Formulajones]

I'd want a fuel pressure gauge on it and duplicate the problem first. Just to see if it's even fuel related at all.

Something tells me it is with the year old gas in it but a gauge will help diagnose.
Even so, I'd want that gas out of the tank if it were mine either way .

I can't even leave fuel in the Nomad for 4-5 months and it smells like turpentine and starts making the needle and seats in the carb stick. So I have to make sure I run that thing every couple months and try not to keep more than 5 gallons of fuel in it. Luckily the factory tank has a drain plug, and I've had to use that more than once LOL

[25stevem]

He has posted that last season he treated the fuel with Sta-Bil, how well such works I don’t know as I have never used it, besides bad fuel would act bad all the time the motor was running.

[Formulajones]

Originally Posted by 25stevem

He has posted that last season he treated the fuel with Sta-Bil.

Ya that stuff isn't all it's cracked up to be. It's never "stabilized" the fuel for very long when I've tried it.

Better off treating it with some 2 cycle engine oil and add some lubricity.

[JLMounce]

does it die suddenly or does is hiccup and stall?

If it's dying suddenly, I'd definitely be looking at the ignition, probably the coil. If it hiccups and stalls in a whimper, that would lead me towards fuel related issues.

I chased heat related fuel vapor issues in my 69 Firebird for a long time. The engine bays on these cars are small, constricted and trap a good amount of heat. It can be difficult to deal with when using modern fuels that are more volatile than the fuels the car was designed to run on. If the car runs at or above 190 degrees on the water temp, it's really only a matter of run time before you soak that heat into the fuel and start to boil it. If that is the issue you are running in to, there are things you can do to increase the amount of run time you have available on a hot day.

Phenolic/wood carb gasket or spacer
Phenolic fuel pump gasket
Wrap your fuel lines in heat reflective material
If the car is not currently equipped, run a fuel or vapor return line back to the tank
If you have one of those glass fuel filter's anywhere, get rid of it

As mentioned though, this could be related to other things that don't like heat, so you'll want to check all of that.

[69f bird]

Thank you for all of the responses. A few answers:
All new wiring, distributor, cap, etc. Under cap Electronics. When it runs, it generally runs at a reasonable temperature. The engine was built, and all the new electronics, lines, wiring (all harnesses), etc. were installed 2-3 years ago. Paul Spotts built the engine, new water pump, clearanced the water pump plate, has a stock fan shroud, new clutch fan, upper and lower baffles, new radiator, the thermostat is 180 I believe. Last year, even in 90+ degree temperatures, it ran around 190 all the time. The crossovers in the heads were aluminum filled.

When it dies, it is a hiccup and stall. When I pump the accelerator when the car is stalled, and then try to start, it wants to start, and then hiccups again. It definitely feels fuel related and not spark. It is the in-carb fuel filter, and it was clean. I have to figure out how to add a temporary fuel pressure gauge. The entire fuel setup is all new stainless lines that I do not want to damage.

[JLMounce]

I have read unsubstantiated reports that I have not been able to independently verify stating that ethanol content in pump fuels may currently be well above 10%. As you add ethanol to petroleum gasoline, the mixture turns to vapor at much lower temperatures until you get sufficiently close to pure ethanol which withstands temperature much better than even pure gasoline.

Refer to diagram on page 2.
https://www.grabner-instruments.com/...5-e640bdc7e338

If the fuel you have in the tank is not only old, but is a blended fuel of e10 or higher, you reach a vapor/liquid ratio of about 35% (and the point at which vapor lock starts to become a concern) at around 137 degrees Fahrenheit. The 5.5 to 7 psi of fuel pump pressure buys you a little bit more temperature handling while the fuel is under pressure, but not a lot.

As you can see, even if your engine runs at the number on a 180 degree thermostat, it's not a matter of if, but rather when the engine and fuel system components soak enough heat to turn your liquid fuel to vapor.

You have a couple options on how to combat this:
1. Source pure gasoline without added ethanol
2. Convert to E85 which will withstand turning to vapor at slightly higher temps than pure gasoline
3. Modernize the fuel delivery system to work with modern pump fuels. This means EFI with a fuel pump and fuel lines capable of withstanding some percentage of ethanol and providing enough line pressure to substantially increase the fuel's boiling point, typically 43-58psi)

[Formulajones]

Originally Posted by 69f bird

Thank you for all of the responses. A few answers:
All new wiring, distributor, cap, etc. Under cap Electronics. When it runs, it generally runs at a reasonable temperature. The engine was built, and all the new electronics, lines, wiring (all harnesses), etc. were installed 2-3 years ago. Paul Spotts built the engine, new water pump, clearanced the water pump plate, has a stock fan shroud, new clutch fan, upper and lower baffles, new radiator, the thermostat is 180 I believe. Last year, even in 90+ degree temperatures, it ran around 190 all the time. The crossovers in the heads were aluminum filled.

When it dies, it is a hiccup and stall. When I pump the accelerator when the car is stalled, and then try to start, it wants to start, and then hiccups again. It definitely feels fuel related and not spark. It is the in-carb fuel filter, and it was clean. I have to figure out how to add a temporary fuel pressure gauge. The entire fuel setup is all new stainless lines that I do not want to damage.

190 is getting pretty warm for pump fuel with a carb and mechanical fuel pump.
Good suggestions here mentioned to combat vapor lock, but even with other precautions it's probably still going to show itself in certain situations with an engine temp of 190. I tend to run our engines cooler and actually get away fine with pump gas on our daily driven cars with carburators and mechanical fuel pumps. But it takes a good mechanical pump that delivers good fuel pressure, and good free flow fuel filter (I use a marine style cleanable stainless screen), and a good fuel sock in the tank. I use the really large socks that GM had in the trucks back in the 70's. All in an attempt to help the pump deliver fuel as easily as possible. I make sure those pumps are delivering 7lbs or more too. If you get a weak one that only makes 4-5 psi, it's going to be a problem, and I've had a few of these cheap mechanical pumps that do just that.
Things people don't think about but little things that add up.

Of course I restrict or limit the heat cross over, insulate the carb etc.... On the Pontiac I have been running the RAIV intake for a few years now with it's separate heat cross over and it's been fantastic for this very reason. Not only keeping heat entirely out of the intake but I still have a functional divorce choke for those cold winter day starts.

Lots of things to look at and play with. Depends on how badly you want to keep that carb and mechanical fuel pump and how often you want to drive the car in the heat.

Of course an easy solution is a big pump in the tank and go EFI. With 60 PSI the fuel doesn't care so much about heat.

[Sirrotica]

If you feel the stalling in heat related I would buy some of the 1/2 inch ID pipe insulation, and cover the lines to see if the stalling is affected:

Ljnk: https://www.homedepot.com/p/Everbilt...5812/204760811

In 1977-79 Pontiac had factory fuel lines from the fuel pump to the carb that were foam insulated for preventing vapor lock.



My parents had a ford motorhome that was so sensitive to ambient air temps, the only time they could travel was after sundown. I insulated the whole fuel system, and built an air intake under the front bumper to duct cool air to the carb. I ran the fuel lines inside the duct to cool the fuel as well as the ducts blew cool air directly onto the front of the fuel bowl.

This solved the vapor lock as well as increased the mileage about 1 1/2 MPG. They lived in Phoenix, so it was tested under the absolute worst possible conditions. No further problems after revamping the fuel system..........