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How to fix Vapor locking from happening

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ScottFromNH

Senior Member
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Hey everyone,

I have a 1973 spitfire 1500, that up until today has been running great. Today I started my car and pulled it out of the garage and let it run outside for a while as I haven't ran it in a few days.

Well my car stalled and I noticed that both my fuel filters were empty of gas. I tried to start it again and pump more gas into them however it didnt work. So I was starting to think either the system is vapor locked or my fuel pump crapped out.

Well after pushing the car back into the garage and leaving it there for a couple hours I went back down and checked on it and my fuel filters were full and the car started right up and ran fine.

I am rebuilding this car and have replaced the fuel tank, the filters, the fuel line from the tank to the pump, the fuel pump and the line heading to the carb. So my question is how can I prevent vapor lock from happening or am I missing something else that is causing this?

the temp today here in NH is 94 and sunny with 62% dew point.

Any help or ideas would be great, the last thing I want is to get the car finished and take it out on a hot day and run into this again.
 
we use to wrap tin foil around the gas line, kind of like a heat shield. are you sure your tank vents not clogged up? and you could put a heat shield under the carb bowl or carb bowls.

Hondo
 
thanks Hondo,

not sure about the tank vents, not quiet sure what they look like, I have 2 canisters on the passenger side of the car in the trunk by the tank. one is a black canister metal and the other is a white plastic filter looking device that seems to have brown dust in it. are they the vents you are talking about? I can take a picture and post if needed.
 
It could very well be junk in the tank clogging stuff up if the tank hasn't been cleaned out or replaced. A fuel problem like you are having should be fairly easy to track down. Are your filters before or after the pump? I would run it again until it stops, then pull the fuel line before the fuel reaches the pump and see if gas comes out. If not, the fuel line is probably plugged. I have had rubber hoses separate and collapse, so if any rubber is in the line that is old, replace that.
If gas comes out of the line you took off, the fuel pump may be clogged or bad. If you aren't getting any flow of fuel from that line you took off, open the lid to the fuel tank to vent it and see if it flows then. That will tell you if it is a venting problem. If little or no gas comes out that line, blow back through it until you hear the gas bubbling in the tank. Gas will come out then. That shows you have junk clogging the line, and you need to clean out the tank.

Dan B
 
Hey Dan,

Actually its a brand new tank I just installed it about a week ago. I have a fuel filter right out of the tank and then I have one right before the carb,

The line is actually steal fuel line from the tank to the pump with little end of fuel hose connecting the tank and the pump.

ok I am also going to post a photo as I have 3 times that the return from the carb line connects to that I am not sure what they are of they are for venting. will have the photos up soon.

thanks for the help.
 
Ok, new tank should be clean. Have you run it until it stalled again? I think I would try that and then pop the tank lid to see if there is a vacuum in there. Was the filter near the tank empty before?
 
Ok I took photos of what I think are vent filters, however not 100% sure. They are connected to a line that runs the length of the car to the carbon canisters by the carb.

DSC00741.jpg


I tried to get the car to vapor lock again however it didnt work this time as the sun has gone down some since this morning,

I did however noticed that my fuel filters are never really full of gas not sure if that is normal. Also I noticed the fuel filter after the fuel pump going to the carb has air bubbles coming out of it when gas is being pushed in to the filter. Is that normal or do I have an issue with my pump?

I got the pump from Victoria british and make sure the armature of the arm that goes inside the engine was exact as their seems to be 2 types of pumps?

I tired unplugging the vent (or what I think is the vent) to see if the fuel filter by the tank ever fills up but it usually only fills about 3/4

any ideas.
 
In your picture it looks like you are running fuel thru your separation tank for your EVAP system. That could be your problem, who knows what was inside that.
 
ScottFromNH said:
I did however noticed that my fuel filters are never really full of gas not sure if that is normal.
Click to expand...
If the filters are mounted horizontally (as usual), then that is entirely normal. The fuel level will rise to cover the outlet port and no more. It may rise some more later, after driving the car (and sloshing fuel around to uncover the port), but it generally takes weeks for it to entirely fill the filter.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Also I noticed the fuel filter after the fuel pump going to the carb has air bubbles coming out of it when gas is being pushed in to the filter. Is that normal or do I have an issue with my pump?
[/QUOTE]
That sounds less normal, unless perhaps the system was still purging air from the other filter. Running a filter before the pump is generally a bad idea anyway, as any pressure drop across the filter will tend to aggravate (or even cause outright) vapor lock.

Might not be the pump, though. Could be anything that lets the system suck air, like a cracked hose or loose joint. Sometimes they will leak air in without leaking fuel out.
 
Hi guys.

Mallard, No the photo I have posted is just the return from the carbon canister in the engine, I just didn't know what those items were. The white item when you shake it brown powder comes out of it and I don't know if that is normal and haven't been able to find a replacement. The fuel line is on the other side of the tank.

TR3Driver,

Ok thanks I will remove the filter that sits between the tank and the pump and also check all the lines to make sure the connection is tight and can stop any leaking air and see if I can cure the bubble issue first. Thanks for the info on the filter and if its horizontal like mine is that it will take a while for it to finally fill.

Thanks for the Emission guide I am looking at it now and i noticed in the diagram I have the vapor separator (black container) but no white filter looking device. so maybe I will remove that also and just hook it up like it shows.

if the rain stays away on Saturday I will be working on it some more and keep you guys posted or have more questions lol
 
The fuel pump failed on our '72 Spit shortly after getting the car as a project. I was trying to get the car back on the road cheap so put a cover plate on the block and used an electric pump that I already had. We normally have days in the 90s down here and I have yet to experience vapor lock. A local acquaintance of mine with a 1500 Midget (same engine as yours and mine) had no luck preventing fuel problems by insulating the lines.

By all means sort the emissions plumbing out as Randall suggested. And check that the "top cover gasket" on your pump is intact (assuming you have the pump that can be taken apart). However, keep in mind that you can switch to an electric pump mounted in the boot if necessary. A boot mounted electric pump is relatively cool and operating as a pusher is less likely to vapor lock.
 
I have a TR6 and purchased a carter electric fuel pump in 2006 and have had no problem except that you can here it humming(could be a good thing since I know its working) and had no problem,

If I ever purchase another one I would get the same one thats on my 97 chris craft boat, its a carter too but about 6 inches long and about 2 inchs in diameter and made for carburators, since my boat has a carb on it, its much quieter

Hondo
 
I am casting out a problem that someone must have experience with: fuel vaporizing before the float bowl. I think the hot radiator on a hot day is vaporizing the fuel where the fuel line runs around the front of the engine underneath the thermostat housing. Is this a common problem? Would running the fuel line from the pump around the back of the engine and reversing the float bowl lids solve this problem? Any advice will be MUCH appreciated. I have stalled out on the highway a couple times. Let the engine cool down for hours before it would start and run again. It never occurs on a cool morning.

Another point is that my float bowl lid vents are not piped to the air filters as shown in the parts catalogue. Could that contribute to vaporlock stalling of the engine given any fuel vapor would not be directed to the air intake. I thought that extension of the float bowl vent was for air pollution control. Maybe not🤔.
 
I ran my fuel line at the back along the square section in front of the battery on both SU’s and now webers.
just swapped the float bowl lids over. Works fine. But whether that’s your vaporisation issue is questionable. Vaporisation that affect running us usually the carbs and a simple heat shield between carbs and exhaust helps.
 
I wrapped the fuel line between the pump and the carburators with aluminum tape and added foam cups (also with aluminum tape on the outside) to the fuel bowls. That fixed my fuel vaporization problem.
 
Anything that reduces heat to the fuel line will help, incrementally. The heat shield under the carbs is the biggest help to prevent vapor locking. Then, wrapping the line. Taking the mechanical pump out of the fuel circuit is next. It adds a good bit of heat. Re-routing the line would be a last resort...a lot more work for no more help than wrapping the stock line.

I don't think the direction of your bowl venting has any affect on vapor locking.
 
If you have a clear plastic inline fuel filter mounted between the thermostat housing and the float bowls, I highly suggest replacing it with a full length of 1/4" ID fuel line. The position of that filter is directly in the heat from the radiator and just above the radiant heat from the exhaust manifold. Not to mention, it is not original.

The fuel in the line is under low pressure and keeps the fuel from vaporizing. But, once it reaches the open space in the filter, it looses that pressure and vaporizes. Ask me how I know.

Also, make sure your fuel lines from the fuel pump are routed correctly around the thermostat housing without touching (hot) bits of the engine

Bob
 
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One other thing to note, heat and gasoline can combine to create one of two problems (both related to the Reid Vapor Pressure (RVP) of the gasoline).
  1. Vaporization (aka vapor lock): this occurs in the fuel line and results in a lean mixture as the fuel pump cannot push vapor - and the engine starves for fuel. Modern cars avoid this with high pressure fuel lines to fuel injectors. Modern cars also have a return line to the gas tank which keeps the fuel continuously circulating though the lines before it has a chance to absorb too much heat.
  2. Percolation: this is when the fuel boils in the carb body, float bowls, etc and results in an overly rich mixture. This is usually accompanied by a heavy gas smell under the hood. Again, modern cars have high pressure fuel injectors so no oppty for the fuel to boil anywhere in the system.
The higher the RVP, the more likely it will vaporize/percolate. RVP of gasoline is higher today than it was in the 1960-70's Ethanol in today's gas raises RVP as well. Also, the EPA mandates higher RVP in the winter to assist cold starting - normally sold Sept 1st to May 1st. So, if you are burning a tank of winter blend fuel on a particularly warm spring day, guess what?

Bob
 
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Good to see someone else making the distinction between vapor lock and percolation.
 
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