[GOAT WHORE]

Running a Holley ultra 950 hp.
1/2" fuel line (aluminum) from tank to Robbmc 550 mechanical pump with return. -6 an from there to robbmc filter to carb.
Never any problems in Portland where elevations are around 500-1000 ft. Out here in Colorado after driving for long periods in the elevation and heat fuel fill flow out the vent tube. Squirters still work and bowls are full.
I can wait a few minutes and hold gas pedal to the floor and it will start and run for a couple of minutes before acting up again. Can see heavy vapor coming out of vent tubes.
Also noticed that after sitting for a few hrs most the fuel had evaporated out if the front bowl.
What's happening here? I mean I know it's flooding out but is it all raw fuel or could it be vapor also that is doing harm?
Any advise would be helpfull.

[AG]

Fuel boils at a lower temperature because of the elevation. Water boils at 193°F at 10,000 feet.

[pggto]

Do you have any sort of spacer under the carb? A phenolic spacer or something that doesn't transfer heat might help.

[GOAT WHORE]

Yes I put on a 1" aluminum spacer from Wilson manifolds. I had this same problem 2 yrs ago and it is much better now but still does it. I think I might try to find a wood spacer.

[Zimtok]

Originally Posted by GOAT WHORE

Yes I put on a 1" aluminum spacer from Wilson manifolds. I had this same problem 2 yrs ago and it is much better now but still does it. I think I might try to find a wood spacer.

An aluminum spacer will transfer the heat.
A wooden or phenolic spacer will reduce the heat transfer.


.

[GOAT WHORE]

Wow, what a day. Acted up almost immediately. Temps were hot and around 6000+ ft of elevation. On the ragged edge most if the day.
As soon as we dropped down below 5000 ft things got better. It was 104 coming into Vegas but at only 2000 ft everything was fine. Got to figure this crap out.

[shaker455]

I think AG summed it up.

insulate everything

[torqjunki]

An insulating spacer under the carb will definatly help. I did some research a while back and found that teflon had the best insulating properties in a material that could handle the heat and of course function as a spacer. I bought a small scrap of teflon sheet that is 5/16" thick and made a spacer. I also got rid of the mechanical fuel pump. I like the simplicity of the mech pump but it is a fuel heater.

[gtofreek]

Today's pump gas boils anywhere from 100°-150° depending. When the fuel is in the fuel line, under pressure, it doesn't boil, but it builds heat to above it's boiling point. As soon as it enters the carb, it is no longer under pressure, and it instantly starts to boil. As the fuel boils[picture a pan of boiling water] the float bounces around in the fuel bowl as a result. This causes fuel to keep coming in until it overflows and floods out. You need to do things to insulate the carb and fuel lines so the fuel doesn't get hot enough to boil. I have had to use water pipe insulation from the hardware store to insulate the fuel lines and fittings, and phenolic spacers to insulate the carb. This is a big problem here in Tucson. We have to deal with it all the time. Running a fuel return system will help also as fresh fuel is always circulating so it doesn't build as much heat.

I have found that electric fuel pumps makes starting much harder as the pump comes on when you turn the key on and the fuel starts flooding the engine out before it has even started. A mechanical pump won't do this as bad. I had to install an oil pressure switch to activate the fuel pump relay on one car. That way the fuel pump wouldn't run until the engine ran. Just need a bypass switch to activate fuel pump relay when float bowl is dry.

Too bad you didn't make it a little further south on your trip Greg. Would have been nice to meat you in person!

[GOAT WHORE]

Thanks for all the input guys. Been reading a little about the problem and as some of you have said I just need to keep the fuel cooler as getting a fuel with a higher boiling point is not practical on a road trip like this.
I am going to get a spacer made of different material when I get back as even the aluminum one helped a lot over the last trip. Also going to insulate all the lines nd May go to an electric fuel pump.
Things are great for now and I won't see those elevation again on this trip.
Yah Paul, I will have to get out your way sometime. Maybe Pontiac Heaven.

[torqjunki]

I use the oil pressure switch that GTO freek mentioned above. I have always used it so was'nt aware of any starting problems associated with having it come on with the switch. I use it to prevent the pump from running in the event of a crash.

[PunchT37]

I had a fuel boiling problem. Used to put my hand on the fuel bowl and had to take it off very shortly afterwards. I added a 1 inch open wood specer. Now, I can hold my hand there how ever long I want. Still hot but, WAY cooler than the metal spacer.
Cut down a lot on the boiling problem but, not all together gone.

[Blued and Painted]

The japs used a shield to keep radiant heat away from from the bowl BITD. In combo with an insulated spacer, it should run cool.
http://www.summitracing.com/parts/HLY-108-70/

[toddmoll]

I had the same fuel boil problem with the tripower on my 66. I milled some spacers from 3/8" phenolic and it fixed the problem. Hottest day out since the fix was 105 and fuel was not boiling. Without the spacers it would boil at around 98-100.

[GOAT WHORE]

The heat is not the only thing, it's elevation. It was around 108 when we came into Vegas and no issues. Reason, only 2000 feet not 8000.

[Formulajones]

You can insulate and shield things everywhere, and it helps. But I've found the biggest and best cure is to run a return style fuel system. This keeps the fuel circulating during idle conditions when the needle and seat are closed, so the fuel isn't sitting stagnent in the line and collecting heat. All you have to worry about then is a short fuel line from pump to carb, and the fuel in the carb itself.

Return style systems didn't really become main stream until 1970 (california) and 1971 (all 50 states) with the introduction of the charcoal vapor canister. So most of your pre-1970 cars don't have a return, and these are the cars I see vapor lock and perculating fuel issues with 99% of the time.

If retrofitting a return style system isn't feasable, then you'll have to insulate things best you can and hope for the best. Keeping in mind that ethanol based fuels make the issue worse, as well as running lower octane fuels. If at all possible, no ethanol fuel would be best, and always run the highest octane you can find at the pump.

For a test you can always pump in 5-10 gallons of high octane race gas and see if the issue disappears completely. If so then you're on the right track. Very hard to vapor lock that stuff.

[GOAT WHORE]

Do run a return line and non ethanel fuel made no difference by its self. Kind if hard to do a test run when I live at under 1000 feet and the issues are 6000+ depending on ambient temps.
Like I said, going to run a shield and spacer along with electronic pump. Also going to make sure return line is working properly.

[Formulajones]

Electronic pumps are great if they're in the tank. I don't recommend inline pumps as they run much hotter and contribute to heating the fuel. They also have a much shorter life expectancy, lucky to get 10-15,000 miles out of them continuous use and judging by your long road trips I assume you like to drive it. I'd recommend doing it right, getting an in-tank pump system and be done with it. I only consider in-line pumps a temporary fix.

The only reason an electric pump can help with vapor lock issues is because they run a much higher pressure than most mechanical pumps. Doesn't mean "problem solved", it's more of a bandaid for a bigger issue.

I live at 6,000 ft with ambient temps that reach 100 degrees during summer months, and frequently drive to higher elevations. Not one issue with vapor locking here using stock mechanical pumps and 10% ethanol fuels (on several cars). With a proper working return style fuel system there shouldn't be any issues. Hope you get er' figured out.