Vapor lock (again)

treerootCO

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I am having vapor lock problems again and need ideas. '78 40, 2F, stock fuel tank, confirmed the lines are installed into the tank correctly, tank is clean, all vents are clear and hooked up, no charcoal canister but the line is routed up the firewall above the tank with a small filter on it, gas cap vents, clean filter, no kinks in the line, and I rerouted the stock line so it is no longer under the frame. The fuel line is either stock metal tubing or 3/8 fuel line. I installed an electric fuel pump directly under the tank with the fuel line as short as possible and still gravity fed. The mechanical pump is still installed and works until the vapor lock problem. It has been replaced three times now. Went wheeling Tuesday and the engine was a little hot and each time, the electric pump could not push the fuel unless I crawled under the truck and disconnected the line just before the OEM fuel filer. Each time a rush of air would come out and then the fuel (from the tank side, not the hot engine side on the line). The exhaust is on the other side of the truck. As soon as I hooked it back up, you could hear the fuel running all the way into the carb. I tired pulling the gas cap when it was vapor locked and blew air backwards through the vents into the tank.

Any ideas?
 
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honk

 
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How old is your rubber fuel line(s)? Sometimes fuel line will break down it's inner wall enough to cause a flap of material that can be pulled or pushed up by pump suction or pressure and temporarily block the line. This is only a 'maybe' suggestion, OK? It'll cause some pretty weird things when it happens.
 
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I had the same kind of problem with my 66 Chevelle in college. It was the fuel line that had broken down and was collapsing internally. I am with Honk on this suggestion.

If that is not it, at least you have eliminated the stock fuel pump. By the way, have you thought of bypassing the pump and just running the electric on a trial basis and vice versa? Just an idea for narrowing it down.

This can be a tough one to resolve, with probably a simple explanation that none of us can suggest.

Good luck.
 
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Hey treeroot I had vapor lock in my 60 a couple of years ago because the metal line ran next to the engine, and it got so hot that's what caused the vapor lock. So I went to Lowe's bout some 1/2 inch one side sticky pipe insulation with an aluminum foil on the other side and just wrapped it best I could all down the metal pipe, and bingo that solved the problem. Hope that helps
 

wesintl

 
 
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CruisinTiger said:
insulation with an aluminum foil on the other side and just wrapped it best I could all down the metal pipe, and bingo that solved the problem. Hope that helps
I guess you need to put the sanwiches on the motor earlier to prevent vapor locking is what I'm reading.. :idea:


Thanks BTW.. I'll remember to bring some next time.
 

PabloCruise

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TreeRoot,

Is your carb fan still functioning?

I used to run a quart or two of ATF in my fuel to keep from vapor locking when in NM for the summer...

I think Honk has some good points - how is your rubber?
 
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I had vapor lock problems a couple times, then one winter the line froze. After that, I took the line from my under seat tank (stock '76 position), put on a pet-cock, then a small electric fuel pump with a filter on the input, then a pressure regulator; all this under the drivers seat. Then ran to a glass fuel filter under the dash that I can see from the driver's seat, then through the fire wall to the carb.

No more problems with vapor locking or freezing, easy to trouble shoot and service. The whole fuel system is about 5 feet long, and none of it is exposed to possible damage ( from under the seat to the dash, the line runs through a copper tube, protects the fuel line and power line to the pump from feet, and easy to shape to follow the trany hump and up the side of the heater). The vapor lock and freezing issues are resolved by the closeness of the pump to the tank, the shortness of the total line, and the whole thing is in as close to a controlled environment as possible on an LC.

gary
 

treerootCO

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4 gallons of higher octane fuel seems to completely rid my 40 of the vapor lock demons. The oxygenated 85 Colorado fuel must be a crappy grade fuel.
 

Pin_Head

 
 
 
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treerootCO said:
Any ideas?
It can't be true vapor lock if you have an electric pump at the tank and there is positive pressure in the line after the pump. Vapor lock is when the temperature of the fuel in the line and the suction created by the mechanical pump exceed the vapor pressure of the fuel, so that the fuel is vaporizing (boiling) in the line and the pump is only pumping vapor. If there is positive air pressure in the line between the two pumps, the electric pump is sucking air. The air has to come from somewhere. Either the inlet to the electric pump is obstructed or incorrectly plumbed. Have you cleaned your tank out lately? Any dirt in the fuel filter? Is there any reason you need two pumps?

treerootCO said:
4 gallons of higher octane fuel seems to completely rid my 40 of the vapor lock demons. The oxygenated 85 Colorado fuel must be a crappy grade fuel.
That's wierd. Higher octane fuel is more volatile (octane is more volatile than longer chain hydrocarbons) and is more likely to vaporize at a lower temperature and pressure and therefore vapor lock. Chances are that this observation is only coincidental.
 

AlaskanWheeler

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It seems that the high octane fuel would make sence in why it does not vapor lock anymore. It's my understanding that high octane fuel requires more heat to burn properly then lower octane fuel. That's why high compression motors have a hard time running a lower octane fuel because the fuel pre ignites due to the increased compression (heat). I don't know if this helps or not; you just need to cool your fuel. I had the same problem with my Ranger; I'd have to wait for it to cool off before I could continue on. POS truck
 

nuclearlemon

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my buddy dean had probs with his 78, ran a fuel cooler and no more issues. but he's runnigng a build 350tpi, so i don't know if his was caused by the same thing.
 
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i have a 350 and am having the same sorta probs, it only seems to happen when i hit the dirt roads and wheel it. i have an electric fuel pump, and over the weekend i put some os that heat wrap stuff on the fuel line so will see how that works.
 
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someone told me once to put clothes pins(wooden ones) along the fuel lines,apparently they act as a heat sink.

personally, you have to many corndogs on the grill.... ;)

anyway, mike if you want to try the insulation stuff over the fuel lines.
i have some sittin in my g-rage i can bring to the meeting wednesday night.
not sure how much i have, i can check tonight.
 

AlaskanWheeler

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I wonder if a tranny cooler would be able to handle the pressure? Would get a lot of cooling if you could run one is that fasion.
 
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