Fuel Quality Florida, Carb Equiped Mk-3 Hot Soak Vapor Lock.

[Blue Classic]

I just moved to Florida and have been experiencing a vapor lock on my carburetor equipped 351-W. I changed the thermostat to a lower temperature, installed a heat shield under the carburetor with a new phenolic wood spacer. This made a slight improvement to the problem, but didn’t eliminate it.

In speaking with Holley they said it was the lousy fuel down South with the high content of alcohol in the fuel. They said to install an electric fuel pump with a pressure regulator and a return line.

In talking to people at a local car show who owned Corvettes, an MGB, Dodge Hemis and even motorcycles said they have been having the same issue and have resorted to running E-90 alcohol free fuel. Its not easily available and cost a lot more.

What are you Southern guys doing.

[NAZ]

Let me guess -- got a mechanical fuel pump mounted on the engine. If that's the case, I agree with Holley's recommendation.

[cv2065]

I just moved to Florida and have been experiencing a vapor lock on my carburetor equipped 351-W. I changed the thermostat to a lower temperature, installed a heat shield under the carburetor with a new phenolic wood spacer. This made a slight improvement to the problem, but didn’t eliminate it.

In speaking with Holley they said it was the lousy fuel down South with the high content of alcohol in the fuel. They said to install an electric fuel pump with a pressure regulator and a return line.

In talking to people at a local car show who owned Corvettes, an MGB, Dodge Hemis and even motorcycles said they have been having the same issue and have resorted to running E-90 alcohol free fuel. Its not easily available and cost a lot more.

What are you Southern guys doing.

I have run mechanical fuel pumps on 350's and 383's all day long in Florida and never had an issue with vapor lock. I only run 93 octane, but never E-90. I'm assuming that the car starts fine when cold but has a hard time restarting when hot correct? You could invest in an electric fuel pump, but you need to figure out where the heat is coming from that is boiling the fuel. Maybe you can pull the fuel line right before the filter (think safety when doing this) and crank the engine over right after the pump seems to fail from being hot. If the pump pushes fuel out the line normally, then it will prove that the pump is not the problem. If that checks out, you could try insulating the fuel lines where they are in 'hot' areas. I'm assuming that you are running at least 3/8" tubes and the temps on your engine are correct.

[Blue Classic]

NAZ, you are right, a mechanical fuel pump. We built it in 2004 up in New England with 37,000 miles on it and never a problem. We have moved to Florida and it’s betwee 75* to 90* everyday and I guess the added ethanol causes the gas to boil at a much lower temperature.

Is there anyone that has fitted an electric fuel pump to a carbureted roadster? In tank pump or external?

Thanks NAZ

[Blue Classic]

Hey CV, thanks for responding. I have only seen one other FFR here in Vero Beach in over 4 months. The heat seems to be centered around the fuel pump. A Holly Billet high volume mechanical fuel pump. Pressure runs Around 7.5 psi when I start the car cold. It is o to maybe 3.5 psi when I get back from a spirited run.

I have -6 AN hose from the tank down to the 4” tube. From there 3/8” tube to just under the fuel pump and then -6 AN hose up to the fuel pump, filter and to the carburetor. I have checked engine timing, even retarding it a couple of degrees. Checked float level and idle mixture with no change. I want the car to run on pump premium fuel so I don’t have to worry taking a long trip.

Thanks again for your ideas, you have given me some things to consider.

[NAZ]

Let me explain why I would recommend an electric fuel pump and why I think Holley does too. A engine mounted pump (mechanical or electric) is pulling fuel from the tank , therefor, has a very long run of line that has less than atmospheric pressure. And the longer "suction" line is exposed to heat off the road and engine compartment which heats the fuel and increases its vapor pressure. Fuel has a fairly high vapor pressure to begin with and when you lower the pressure it the fuel line and heat the fuel it is just that much more prone to vapor lock. You can insulate the suction line but you may still find you're on the ragged edge of vapor lock. The pump won't pump vapor (a gas) it will only pump liquid. However, there are lots of cars running a mechanical pump mounted on the engine so it's not an impossible situation but you may have to get creative to prevent hot-soak vapor lock.

Now place the pump at the fuel tank or better yet, in the fuel tank and the long run of fuel line is now under pressure which will help prevent vapor lock. The vapor pressure of the fuel will have to overcome the fuel line pressure in order to turn to a gas and cause vapor lock.

[Blue Classic]

Hi NAZ, that really makes sense and brought back a lot of the old physics class. I haven’t found an in-tank pump for a carburetor application. There are several externally mounted pumps that Holley makes that could work out.
Thanks again.

[GFX2043mtu]

If you are running a mustang tank you can run an oem in tank pump with a Aeromotive A1000 carb return regulator. Run a return line and your all set.

[Blue Classic]

If you are running a mustang tank you can run an oem in tank pump with a Aeromotive A1000 carb return regulator. Run a return line and your all set.

Hey that would make it much easier. That would be a stock in the tank fuel pump with the Aeromotive A1000 Presure Regulator in the return line. Thanks

[CraigS]

I would also look into a pressure regulator w/o a return line. Maybe 6-7 yrs ago the Lexus cars I worked on every day went away from the return line type systems. I never heard why from an official source. I did hear some conjecture of a theory that the gas in the tank is relatively cold. But running it up to the engine compartment, through the fuel logs on top of that hot engine and then back to the tank, was actually putting heat into the gas.

[mike223]

The pump won't pump vapor (a gas) it will only pump liquid. However, there are lots of cars running a mechanical pump mounted on the engine so it's not an impossible situation but you may have to get creative to prevent hot-soak vapor lock.

The vapor pressure of the fuel will have to overcome the fuel line pressure in order to turn to a gas and cause vapor lock.

I did hear some conjecture of a theory that the gas in the tank is relatively cold. But running it up to the engine compartment, through the fuel logs on top of that hot engine and then back to the tank, was actually putting heat into the gas.

All +1.


Speaking of vapor pressure - I have a strong suspicion that since everything late model is fuel injection / high pressure fuel pump / pressurized tank that the vapor pressure of (today's) pump gas is probably considerably higher than it was 30-50 years ago.

To be clear - the boiling point is lower / vapor pressure is higher.

You also get into that on winter gas blends vs. summer gas (and regional blends).

[wallace18]

Living and building FFR cars in FL. has taught me one thing. Use FI or if carb use non -Ethanol fuel. A electric fuel pump will not fix your hot start problem. I know from experience. Trust me. TW

I now only install FITECH FI if customer wants a carb look to engine.

[Pineapplehead]

Curious...is there no real gas available in Florida? I haven't run ethanol in anything I own in more than a decade. Plenty of real gas in Idaho, but plenty of cold in the winter, too!

[wallace18]

Curious...is there no real gas available in Florida? I haven't run ethanol in anything I own in more than a decade. Plenty of real gas in Idaho, but plenty of cold in the winter, too!

You can buy non Ethanol gas in FL. at limited stations. The 10% Ethanol not a problem with FI, only carbs.

[Blue Classic]

Living and building FFR cars in FL. has taught me one thing. Use FI or if carb use non -Ethanol fuel. A electric fuel pump will not fix your hot start problem. I know from experience. Trust me. TW

I now only install FITECH FI if customer wants a carb look to engine.

Ok I’m interested in finding out more in on FITECH FI . What kind of Fuel Pump do you run and is it an in tank pump?
Thanks

[DavidW]

Let everyone know what you find out about FITECH FI. Also if you don't mind tell me how the O2 sensor will attach. I have the FFR headers for my 351w and would have to get a bung installed in the #1 exhaust tube or find someone to custom make headers, then ceramic kote them all over.....$$$$

[wallace18]

Check out my Build thread. You can use an in tank or external pump and install the O2 sensor in the collector side pipe. check post #171 I use a mustang internal pump that fits the tank as is. You can get them from Rock Auto.

https://thefactoryfiveforum.com/show...d-Thread/page5

[RoadRacer]

I haven't seen anyone recommend this product yet, so I'll add my 2c. This fixed my vapor lock on GT40 when idling for a while... fuel lines would simply get too hot.

This particular orange product is very cool (yeah I went there!)

https://www.pegasusautoracing.com/pr...p?Product=3299

[BigUgly]

Blue Classic

I think it would be a lot easier to just move back to New England

BigUgly

[Blue Classic]

Moving back would eliminate the vapor lock problem but a divorce might cost more ��

[Avalanche325]

I am in Florida (further north), have a carb, radical cam, engine mounted fuel pump, I regularly run 10% ethanol and never have a problem.

Here is a long shot maybe:

Are you running a Cobra oval air cleaner? The thin filter that they come with can let the top close off the carb vent tubes when it gets hot. You will think you have vapor lock, but flooding will be the real issue. This happened to me. The cure was a thicker filter.

[Blue Classic]

Thanks for the feed back and ideas everyone.
I installed an electric fuel pump and a pressure regulator with a return line.
First run at 85*f at full operational temperature, stopped and let it heat soak for 15 min. Hot restart was good, with a smooth idle and good acceleration. No vapor lock concern. We have had nothing but rain the last few days but I do believe that the problem is resolved. Thanks again. Loving it here in Florida.

[GFX2043mtu]

Glad to hear everting is working correctly.

[davekp]

This has been discussed at length in the Corvette forum. Basically, the issue boils (hah) down to two problems:
1. If it occurs after a brief shutdown, it is usually a carburetor heat soak problem. What happens is the fuel in the float bowl will actually start boiling over and floods the engine. Some claim they can actually hear the fuel boiling. Holleys are particularly susceptible to this. But it can also be ...
2. If it occurs while the engine is running it is a problem with the fuel line between the fuel tank and the fuel pump. This is due to the fuel in the line being heated beyond the boiling point. Insulating the fuel line to the fuel pump usually solves this.
Some Corvette owners have simply used an old-fashioned electric fuel pump located near the fuel tank to push "cool" fuel to the carb.
On my '65 Corvette I have never had the issue here in Florida, but I do have a radiant shield under the carburetor to prevent boilover.

[Blue Classic]

I have run my car since 2006 in this configuration without any trace of a fuel concern for 36,000 miles. We drive to Florida this past December and in North Carolina the first vapor lock problem was noticed after a hot soak.
Yes Dave, I have over several months tried to isolate the source the heat buildup by installing a phenolic insulator under the carburetor, then an additional heat shield under the carburetor to no advail. Then I tired changing the location of my in line fuel filters, rerouted fuel lines. And as you have clearly said putting the fuel pump back by the tank and pushing the fuel to the carburetor helps. I wanted the additional measure of confidence of moving cool pressurized fuel through the fuel log back to the tank to insure the problem was resolved.
So far so good.

[65 Cobra Dude]

Good to hear you got it figured out.

Henry