Fuel boiling?
Thread Starter
Heel & Toe
Joined: Jun 2007
Posts: 16
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Fuel boiling?
I have a 70 454, and an 81 with a 383 crate motor. With both of these, as well as other vintage cars, I am having fuel problems when they get warmish (not overheated, just normal temp for a hot day). It seems to me as if fuel boils at lower temperature than it used to. Is there any additive that will increase boiling point? Any ideas on other ways to mitigate the fuel boiling issues?
Team Owner
Joined: Sep 2006
Posts: 31,221
Likes: 4,311
From: Westminster Maryland
Hi Robert,
I'll start with an easy one.
70 bb engines used a Q-jet carb and were intended to have a fuel pump with a return line to the fuel tank.
Part of the intent of the return line was to help with a fuel vapor lock problem.
Does your fuel pump have the return and is it hooked up?
Regards,
Alan
I'll start with an easy one.
70 bb engines used a Q-jet carb and were intended to have a fuel pump with a return line to the fuel tank.
Part of the intent of the return line was to help with a fuel vapor lock problem.
Does your fuel pump have the return and is it hooked up?
Regards,
Alan
Racer
Joined: Oct 2003
Posts: 424
Likes: 9
From: Killeen Texas
Years ago, like everyone,, I always used the vent tube, which was 1/4" if I remember correctly, as a return, elec pump w/ a regulator, so the fuel didn't sit in the line and get hot waiting to feed into the carb, then use a vented cap.The old cool cans were used back then f/ Sundays at the track. This is old info/tech and I imagine that the guys on here have better methods now days, but the old method did work.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
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From: Tolland CT
I have a couple threads in the tech section in which I asked the same question, does today's gas boil at a lower temperature causing percolation or vapor lock. Mine is a 70 bb as well. All stock, q-jet, fuel return line, etc. You may want to have a look in the tech section, see if some responses I received may be helpful. I'm still investigating, side tracked with another repair.
Last edited by BBCorv70; Sep 20, 2016 at 11:31 PM.
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With all the alcohol being added to todays fuel ,I would say yes it boils easier, and I dont know if buying octane additives would help. Maybe find some ethanol free gas.
To the mechanical solution, you can add a wood spacer between the carb and intake, you can make sure your return fuel line is connected, you can check the float bowl levels and fuel pressure if you have an edelbrock carb, you can make sure your fuel line is not touching the motor at any point, you can look at buying an Air-gap style manifold that lets air cool the intake. I did all of these to cure my fuel problem, but I did them all at once, so I don't know which one specifically fixed the problem.
I also added a cold air intake to help feed the carb fresh air.
To the mechanical solution, you can add a wood spacer between the carb and intake, you can make sure your return fuel line is connected, you can check the float bowl levels and fuel pressure if you have an edelbrock carb, you can make sure your fuel line is not touching the motor at any point, you can look at buying an Air-gap style manifold that lets air cool the intake. I did all of these to cure my fuel problem, but I did them all at once, so I don't know which one specifically fixed the problem.
I also added a cold air intake to help feed the carb fresh air.
Burning Brakes
Joined: Apr 2008
Posts: 1,222
Likes: 93
From: shelbyville West Michigan
where is the fuel boiling? tank? line? float bowl?
alcohol and gasoline have similar boiling points but different latent heat of evaporation needs. Alcohol takes about 3x more latent heat to change state than pure gas. that's partly why carbs ice up.
even at a 50% concentration of alcohol, the difference in boiling point would only be a few degrees along the curve.
adding some HEET (methanol) would increase the latent heat needs even further.
keep in mind too, that pressure has an effect as well. are you in the mountains? what pressure are you running in the lines?
alcohol and gasoline have similar boiling points but different latent heat of evaporation needs. Alcohol takes about 3x more latent heat to change state than pure gas. that's partly why carbs ice up.
even at a 50% concentration of alcohol, the difference in boiling point would only be a few degrees along the curve.
adding some HEET (methanol) would increase the latent heat needs even further.
keep in mind too, that pressure has an effect as well. are you in the mountains? what pressure are you running in the lines?
Safety Car
Joined: Oct 2007
Posts: 3,729
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From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
the easy answer you must be using the stock 1/4" thick carb. gasket, for thermal Isolation.
failure to do this can create boiling fuel in the carb.
failure to do this can create boiling fuel in the carb.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Ethanol vaporizes sooner than gasoline; so fuels with ethanol will 'boil' earlier. Buy ethanol-free gasoline, if you can find it in your area. Or, install a fuel pump with a return line. That will keep fuel entering your carb cooler.
Another 'do good' thing is to put blocker plates over the heat riser passages in your cylinder heads. You have to remove the intake manifold to do this, but that keeps exhaust heat from getting to the carb area.
Another 'do good' thing is to put blocker plates over the heat riser passages in your cylinder heads. You have to remove the intake manifold to do this, but that keeps exhaust heat from getting to the carb area.
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