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07-04-2005, 09:57 AM
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CC Member
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Join Date: Feb 2002
Location: Dadeville,
AL
Cobra Make, Engine: Sold my EM.
Posts: 2,459
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Not Ranked
Vapor lock at fuel pump
On a particularly hot day at the track last summer, my car started missing and the engine died. Back in the pits, I saw that no fuel was coming from the carb. I disconnected the fuel line and saw that no fuel was being pumped to the carb by the Holley Red electric pump. The pump was mounted high in the trunk and sucked fuel from a fitting in the top of the fuel cell. I put an ice bag on the pump in the trunk and after a half an hour, it started and ran normally. ... Over the winter, I replaced the fuel cell with one with a fuel pickup in a sump at the bottom. I also moved the fuel pump down to a point even with the bottom of the tank. ... Back at the track last week, the car ran great for several sessions, but during a very hot mid-afternoon session after about fifteen minutes of continuous laps (mostly 4th gear averaging about 84 MPH), the engine began to miss again. The fuel tank was half full. As the day was hot and I was tired, I parked the car and let it sit overnight to cool. Next day, in the cool of the morning, it started right up and ran strong for a full 20 minute session. Last night I drove the car two hours at normal highway speeds without any sign of a problem.
On the track, I suspect the combination of high ambient temperature and a fuel pump heated by the demand of pumping lots of gas is causing fuel in the suction line from the tank to the pump to vaporize. If that is the case, I'll need to either find a cooler running fuel pump or find a way to cool it, or both. Before I pick one or the other, have any of you experienced similar problems? If so, can anyone recommend a fuel pump that generates less heat in the fuel line?
__________________
Tommy
Cheetah tribute completed 2021 (TommysCars.Weebly.com)
Previously owned EM Cobra
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor
Last edited by Tommy; 07-04-2005 at 03:26 PM..
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07-04-2005, 11:42 AM
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CC Member
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Join Date: Nov 2000
Location: Houston,
Tx
Cobra Make, Engine: Unique FIA
Posts: 2,064
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Tommy,
Are you sure the tank is vented correctly? If not it could be developing a negative head pressure (just a wild a$$ guess) I would consult with the pump manufacturer as to possible causes before going crazy.
Steve
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All my ex's live in Texas
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07-04-2005, 03:25 PM
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CC Member
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Join Date: Feb 2002
Location: Dadeville,
AL
Cobra Make, Engine: Sold my EM.
Posts: 2,459
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Not Ranked
Steve -
Thanks for the suggestion. But yes, the tank is properly vented. If venting were the problem, it would appear even in cooler weather. This is a hot weather phenomenon.
__________________
Tommy
Cheetah tribute completed 2021 (TommysCars.Weebly.com)
Previously owned EM Cobra
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor
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07-04-2005, 04:31 PM
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CC Member
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Join Date: Dec 2003
Location: Gurnee,
IL
Cobra Make, Engine: Kirkham #259
Posts: 1,396
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Not Ranked
You need a Return line to the tank.....
Morris
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Morris
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07-04-2005, 05:17 PM
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CC Member
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Join Date: Nov 2000
Location: Houston,
Tx
Cobra Make, Engine: Unique FIA
Posts: 2,064
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Hey Morris,
That can't be right...... It makes too much sense! 
__________________
All my ex's live in Texas
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07-04-2005, 06:40 PM
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CC Member
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Join Date: Feb 2002
Location: Dadeville,
AL
Cobra Make, Engine: Sold my EM.
Posts: 2,459
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Not Ranked
Morris -
I don't doubt the wisdom of your suggestion, but the reason it would work isn't immediately obvious to me. Being the curious kind, help me understand why a fuel return line would help.
__________________
Tommy
Cheetah tribute completed 2021 (TommysCars.Weebly.com)
Previously owned EM Cobra
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor
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07-04-2005, 07:54 PM
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CC Member
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Join Date: Dec 2003
Location: Gurnee,
IL
Cobra Make, Engine: Kirkham #259
Posts: 1,396
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Not Ranked
Steve
Common Sense ....what's that....
Tommy
My mission is to teach you how to fish ...not to fish for you....
Read a couple of books and you'll understand.... when fuel percolate.....and how to prevent it....
Morris
__________________
Morris
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07-04-2005, 08:44 PM
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Senior Club Cobra Member
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Join Date: Jun 2001
Location: North Metro Atlanta,
GA
Cobra Make, Engine: 2 dr roadster, V-8, 4 spd.
Posts: 2,780
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Just imagine if you can recirculate perculated fuel to the tank and draw relatively colder fuel from the tank via same circulation....
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07-04-2005, 08:58 PM
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CC Member
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Join Date: Feb 2002
Location: Dadeville,
AL
Cobra Make, Engine: Sold my EM.
Posts: 2,459
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Morris -
Caroll Smith's books don't address your suggested solution. But an extensive search of the Internet did yield an answer. The key is not just a return line. In order to use a return line I'll have to switch from my dead-head regulated style fuel pump (Holley Red) to a return-line style fuel pump and a regulator. According to one source, the return-line style fuel pump runs cooler. ... The fish you threw me wasn't the fish I needed, but it pointed me in the right direction. Like most people, I learn best when I teach myself.
__________________
Tommy
Cheetah tribute completed 2021 (TommysCars.Weebly.com)
Previously owned EM Cobra
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor
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07-04-2005, 09:04 PM
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CC Member
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Join Date: Feb 2002
Location: Dadeville,
AL
Cobra Make, Engine: Sold my EM.
Posts: 2,459
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Not Ranked
Quote:
Originally posted by ToyCollector
Just imagine if you can recirculate perculated fuel to the tank and draw relatively colder fuel from the tank via same circulation....
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ToyCollector -
You can't send percolated fuel anywhere including back to the tank. If it could be pumped, it could be sent to the carburetor. However, I speculate that on a dead-head style fuel pump, fuel that is waiting to be pumped to the carburetor spends more time near the hot fuel pump and is more likely to absorb enough heat to percolate. Fuel in a return-line style pump passes quickly through the pump before going to either the carburetor or back to the tank.
__________________
Tommy
Cheetah tribute completed 2021 (TommysCars.Weebly.com)
Previously owned EM Cobra
"Never attribute to malice that which is adequately explained by stupidity." - Hanlon's Razor
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07-04-2005, 10:35 PM
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CC Member
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Join Date: Nov 2000
Location: Houston,
Tx
Cobra Make, Engine: Unique FIA
Posts: 2,064
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Quote:
Originally posted by Morris
Steve
Common Sense ....what's that....
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Morris,
Such a thing does not exist. Does it.
Steve 
__________________
All my ex's live in Texas
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07-05-2005, 05:33 AM
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CC Member
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Join Date: Mar 1999
Location: penn.,
Posts: 2,561
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try one of them $2 buck inline fuel filters, the clear ones. worked for me many times in the old flathead days
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