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Vapor lock

76k5blazerr

76k5blazerr

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Ok, some of y'all may have seen my thread awhile back about my 72 c10 dying on me, I suspected it was the fuel pump, put a new fuel pump on and just right now it died again, so I'm now sure it's vapor lock, just figured I'd post up here while I'm waiting on my buddy to bring me some gas to prime the carb. I was planning on blowing out all the fuel vent lines tomorrow anyway. So give me the run down on what all causes vapor lock and how I can fix it. I have a 3 line fuel pump if it matters. Also if somebody could tell me where all of the vent lines are at for the fuel pump and tank so I can blow them out I would appreciate it. Thanks.
 
Is the tank still making noise when you pull the gas cap?
Do you have the return hooked up for the fuel pump?
Heat causes vapor lock, make sure fuel lines are away from hot things.

You sure your dizzy is in good working order?
 
K85 Octane said:
Is the tank still making noise when you pull the gas cap?
Do you have the return hooked up for the fuel pump?
Heat causes vapor lock, make sure fuel lines are away from hot things.

You sure your dizzy is in good working order?
Click to expand...
I did the mod on the gas cap where you cut the spring down so now it vents at very low PSI, no more whooshing when i take the cap off, however when I'm driving the truck and sitting at a light or something i can watch fuel vapor coming out of the cap. I think the vent lines are all clogged, return line is hooked up from fuel pump. Pretty sure dizzy is fine as the engine runs great, except when it vapor locks. We got the truck started and i drove home and when i was backing down the driveway it vapor locked again, primed it again and this time gas came out the side of the carb. Maybe i need to rebuild it?
 
I would start with the vent lines. Chase them down and just replace them. Then go after the carb. Is this the original 2 barrel?
 
K85 Octane said:
I would start with the vent lines. Chase them down and just replace them. Then go after the carb. Is this the original 2 barrel?
Click to expand...
I'm starting to think that my carb is too close to the intake and that's what's causing vapor lock. How could I identify this as the problem? Because last night when it vapor locked and we poured some gas in the carb when the gas when down the carb it started steaming. Carb seemed much hotter than it should have been. Thinking I may need a 1/2-1 inch spacer. What do you think?
 
You already have the 3 line pump which should help the pump stay cooler and the fuel passing thru it.
I run a 1/2 edelbrock wood spacer under my Qjet to prevent (help) with fuel boiling in the carb after shutdown.
I could hear it gurgling.
Even tho I did not suffer from vapor lock the spacer helped the fuel boil issue.

Certainly can't hurt to try one.

This new fuel with ethanol is more volital and burns leaner/hotter than the fuel our older vehicles were designed to run on.
 
blazer74 said:
You already have the 3 line pump which should help the pump stay cooler and the fuel passing thru it.
I run a 1/2 edelbrock wood spacer under my Qjet to prevent (help) with fuel boiling in the carb after shutdown.
I could hear it gurgling.
Even tho I did not suffer from vapor lock the spacer helped the fuel boil issue.

Certainly can't hurt to try one.

This new fuel with ethanol is more volital and burns leaner/hotter than the fuel our older vehicles were designed to run on.
Click to expand...
Ordered a 1 inch plastic spacer last night. Hopefully it fixes this because it's getting real annoying.
 
Good luck man. I got so sick of vapor lock that I went LS swap. :angry1:

To be fair, I wanted to do the swap anyway for a variety of reasons but that is what finally pushed me to get rid of the carb forever. I just couldn't solve the problem. Hope you have better luck.
 
76k5blazerr said:
No kidding, when I fix this problem I'm either gonna run premium fuel (which I think doesn't have ethanol) or go to an ethanol free filling station, we have several around here.
Click to expand...


Good luck with trying to get fuel without alcohol, even the places that say they don't usually do.:doah:And the alcohol is just part of the issue. The bigger problem is the reformulation of fuel for modern cars, modern emission systems and modern emission standards while complying with EPA standards on which chemicals can even be used in fuel. Works great for injected cars but not so much for us old carb guys.

Do you have any fuel filters before the fuel pump??
Sounds like the problem is a fuel supply issue to the fuel pump, more than a carb issue. ANY restriction before the fuel pump WILL cause the fuel to boil in the fuel line before the pump. (remember when you put liquid in a vacuum you lower the boiling point) Check the sock in the tank, if it's looking sad replace it, if it looks dirty replace it. In the end you may end up putting an electric pump under the cab and eliminate the stock pump.

Venting out the gas cap is normal, the hotter it is the more it will vent and stink.

The only things that I've found that help with hot running loading up are:
1 use a phenolic or wood spacer under the carb to help insulate the heat.

2. mount a return style filter near the carb to help keep the fuel as cool as possible before it goes into the carb.

3. Get rid of the stock mechanical fuel pump/fuel heater.

All of these suggestions will help but will not fully fix hot weather fuel issues, fuel injection is the only real fix. :o
 
bigblock72 said:
Good luck with trying to get fuel without alcohol, even the places that say they don't usually do.:doah:And the alcohol is just part of the issue. The bigger problem is the reformulation of fuel for modern cars, modern emission systems and modern emission standards while complying with EPA standards on which chemicals can even be used in fuel. Works great for injected cars but not so much for us old carb guys.

Do you have any fuel filters before the fuel pump??
Sounds like the problem is a fuel supply issue to the fuel pump, more than a carb issue. ANY restriction before the fuel pump WILL cause the fuel to boil in the fuel line before the pump. (remember when you put liquid in a vacuum you lower the boiling point) Check the sock in the tank, if it's looking sad replace it, if it looks dirty replace it. In the end you may end up putting an electric pump under the cab and eliminate the stock pump.

Venting out the gas cap is normal, the hotter it is the more it will vent and stink.

The only things that I've found that help with hot running loading up are:
1 use a phenolic or wood spacer under the carb to help insulate the heat.

2. mount a return style filter near the carb to help keep the fuel as cool as possible before it goes into the carb.

3. Get rid of the stock mechanical fuel pump/fuel heater.

All of these suggestions will help but will not fully fix hot weather fuel issues, fuel injection is the only real fix. :o
Click to expand...
Ok, update on my problem. So this morning I finally got a chance to install the carb spacer. It's a 1 inch phenolic type. Got it on, still have to lengthen the choke rod that goes to the intake but that doesn't effect it running. So I get it on, truck cranked right up and ran good like it always does cold, took it around the neighborhood, about 5 mins into my drive it dies out, cranked back up though with a little pedal pumping, I didn't have to pour gas in the carb like usual, then I proceeded to drive about a 1/4 mile and it died again, cranked it, it ran, put it in gear it died. Did this like 2 more times before I finally got it to go in gear and drive, then I made it about 1/2 a mile back into my part of the neighborhood, go up a hill and at the top of the hill about 1/4 mile from my house it dies, I crank it, won't start. Then I push it to the side of the road, try cranking some more and it won't even turn over. Nothing happened when I turned the key, so I figured the heat had got to the starter or something and walked home, will go back up the street in a bit once it cools down and hope it starts. So basically, the spacer was no help. My next step is to buy some 3/8ths brake line and bend up all new fuel lines and as soon as they come down from the tank, run them through a hole in the frame and run them outside the framerail all the way to the motor then back in to the fuel pump. My fuel lines are currently about an inch or inch and a half from the headers, but when it vapor locks they feel only remotely warm. So guys I'm getting really irratated with this. Any other ideas y'all got?
 
No, but this issue isn't spark related. I'm able to pour fuel in the carb when it dies and it fires up. Also, went up to the truck about an hour ago and it cranked up. Got it back in the garage and went and bought a new steel line to bend up outside the frame rail. Hopefully this works.
 
I'm no expert, so take this with a grain of salt, but when I was dealing with this problem I was told that the problem was between the pump and the carb. I don't know that replacing all the other line will help. If the line is only warm to the touch I would think that wasn't the problem.

I think someone suggested putting a return line in as close to the carb as possible. That makes sense to me as it would keep the fuel moving (not just sitting in the line waiting to be used) and also cool the fuel as it gets sent back to the tank.

I hope you figure it out man. Super frustrating for sure!
 
ashman said:
I'm no expert, so take this with a grain of salt, but when I was dealing with this problem I was told that the problem was between the pump and the carb. I don't know that replacing all the other line will help. If the line is only warm to the touch I would think that wasn't the problem.

I think someone suggested putting a return line in as close to the carb as possible. That makes sense to me as it would keep the fuel moving (not just sitting in the line waiting to be used) and also cool the fuel as it gets sent back to the tank.

I hope you figure it out man. Super frustrating for sure!
Click to expand...
I have a return line coming off of the pump already. What I don't understand is that the fuel line from the pump to the carb is routed the factory way and it is the same as the one in my blazer and I've never had this problem with it. What do you mean when you say a return line close to the carb? Like put on one of those single in dual outlet fuel filters and run it back to the tank?
 
76k5blazerr said:
Like put on one of those single in dual outlet fuel filters and run it back to the tank?
Click to expand...
Yeah, I would give that a try before replacing all that line.
Like I said, I never solved the problem myself until I went FI, but that is something I didn't try and it seems like it might work. :dunno:

Bigblock72 was the one that made the suggestion and he knows his shit from what I've seen over the last couple of years. :)
 
ashman said:
Yeah, I would give that a try before replacing all that line.
Like I said, I never solved the problem myself until I went FI, but that is something I didn't try and it seems like it might work. :dunno:

Bigblock72 was the one that made the suggestion and he knows his shit from what I've seen over the last couple of years. :)
Click to expand...
So I geuss what I should do is buy a dual outlet fuel filter and then run it down to the steel return line back to the tank and then just plug off the return port on the pump?
 
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