Howdy guys,

Now that that summer heat has really kicked in here in Tucson (105-112) we have started to have problems with our fuel vapor locking--at least I am 99% sure that is what is happening. Wasn't a problem until the last week or two when it has gotten really effing hot. The engine loses power, then stalls altogether, and restarts after a good long cooling period.

We have a 351W with a mechanical fuel pump and a brand new Edelbrock carburetor. We have a mechanical fan on the front of the water pump pulley. Our engine is running consistently at about 210 according to the hand-held temp gun. We have a stock temp gauge, so that is next to useless as far as determining an actual temperature value.

I'm pretty sure I have a vented fuel cap, at least there is no rush of air when we take the cap off to fill it after driving a good while. Our fuel lines are 5/16" stainless steel from the tank to the fuel filter (which I have checked and cleaned as recently as this morning without effect). The filter is in the engine compartment down low by the frame rail on the driver's side. From the filter to the mechanical pump (driver's side of the engine, so about 8" from the filter) we have steel braid covered rubber line. From the pump we have more 5/16" steel line running upward, just in front of the valve cover and just below/behind the AC compressor. The steel line ends just inboard of the valve cover and from there rubber hose (with no steel braid, just plain) routes around the front of the carburetor and air cleaner to the passenger's side of the intake manifold. It then runs aft, inboard of the PS valve cover and to the fuel port on the carb. None of the fuel line is insulated, unless you count the steel braid from the fuel filter to pump.

All that detail leads to my question. Is there any way to determine WHERE in all that plumbing the fuel may be vaporizing? The line that is most exposed to heat is from the pump to the carb, but that is the pressure side (after the pump), so it just seems unlikely to me that the fuel could be vaporizing in that run of plumbing, at least while the engine is running. But, still, I'm sure it gets really hot along in there.

Yesterday when my son and I were stranded on the side of the road, we pulled off the fuel line from the carb and cranked the engine. No fuel came out of the line. Eventually my buddy towed us two miles home. After it cooled (overnight actually, we had a dinner to be at last night) it started right up. It just seems that the fuel would not vaporize in that short run, especially with the line disconnected. I don't know... Could the fuel be vaporizing INSIDE the pump possibly?

I've heard of a variety of solutions, from wrapping the lines with aluminum foil to dissipate the heat better, all the way to getting a new electric fuel pump that is way back near, or even in, the fuel tank. I don't really want aluminum foil in my engine bay, you know? It's gonna look crappy and annoy me. Is there some kind of line that dissipates heat better? Would steel wrapped line dissipate the heat better than the rubber line we have up there near the intake manifold and the valve covers? Should I reroute the whole thing so it stays well away from the manifold and valve covers and come in to the carb from the back of the engine? Do I need to insulate the fuel lines I already have?

That's a lot of questions and options. What is the right thing to do here, besides getting fuel injection?

Thanks! Tyler

 

Yes and maybe.

In a really harsh situation like PHX, the best solution is to run a small amount of fuel back to the tank, from right in front of the carb. This keeps the pump cool(er) by maintaining a constant higher flow. There are several ways to do that, but it depends whether you have a return connection at your tank? Are you using a stock tank or one out back?

An electric pump is a better idea, but you may still need a recirc line back to the tank. Are all your lines inside the frame rails?

 

Howdy Ross,
I don't have a stock tank. It is back behind the rear axle. But I am 99% sure there is NOT a return connection. But couldn't I put one in the fuel supply line some where back there with a T connection?

And yes, all my fuel lines are basically inside the rails.

t

 

Ideally you want to draw fresh "cool" gas out of the tank with the pump, and put hot recirculated gas back into the tank. Check your fuel sender bung, there may be one there or room to add one.

Your filter on the inlet of the fuel pump isn't helping with the vapor lock issue, if your lines are clean, consider deleting it.

 

So run the engine with no fuel filter? Really?

 

mine was labor locking and I put a 1" spacer underneath the carb and wrap the lines with some fuel line wrap and added electric fuel pump so far all is good..... I live in fl and have Ac in truck also,I RUN TO ELETRIC FAN one for the AC and the other for the engine it run around 190 degrees in town driving with air on Hope that may help and good luck (this is in a 55 f-100 with a 302)

 

I remember my dad always had a milk jug full of water . Seems the old flatty would vapor lock and he would use the jug to cool the pump down. Might be worth a try till you figure out what you want to do.

 

The filter should be after the pump where there is plenty of pressure. On the inlet it just exacerbates the vapor lock problems.

 

Ok then. I'll swap it around.

 

Yeah that's what I've started doing. Brake cleaner works great too. It gets really cold as it exits the can. Just gotta make sure I don't spray it on anything too hot so it doesn't flash ignite. I look better with my eyebrows than without.

 

I put wooden clothes pins on my fuel line. Old school fix but it is working for me.

 

I think Ross is right about this. Find a way to run a return from the carb back to your fuel tank. In fact, there are some fuel filters that have a return fitting on them. They were used in earlier Chrysler and AMC products in fact I saw some the other day on a FRAM filter display so I know they are still out there.
Also try adding some insulation around your fuel line. I like the foam-rubber tubing that people use to insulate home water pipes. It's cheap, easy to install, looks acceptable and helps.
I was having what I thought was percolation problems on my carb. Turns out that was not it,even though percolation and vapor lock are different problems, it got me doing some research and picked up some interesting information. If I understand correctly the lower the fuel pressure, the easier it will boil and vaporize with heat. To try to combat the heat, some go to electric fuel pumps, which does a couple of things. It gets the fuel away from a hot, engine block mounted pump, but also, depending on the pump you buy, will increase the fuel pressure. With a higher fuel pressure, it's harder for the fuel to boil. But now that the fuel pressure is raised you will have to lower it again with a fuel pressure regulator, The regulator is adjusted to feed the carb the pressure it wants. There are different types of fuel regulators. I was looking at installing the by-pass type that has a fitting to connect the tank return line to. If you would like more information, on various fuel line plumbing methods, talk to a racer, or there are a number of books on carburetor rebuild and modifications, most of the time this kind of information is in the back of the book.

 

If you're going electric, that is for sure the best bet. It helps the regulator too, because they need flow to control pressure accurately.