Maybe vapor lock. - Chevelle Tech
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post #1 of 40 (permalink) Old Jun 2nd, 20, 4:22 PM Thread Starter
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Mike
 
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Maybe vapor lock.

I feel I am chasing my tail.
I start up the chevelle and it shows 7 pounds fuel pressure on the regulator, go up the road and get it hot with a high speed pass, and pull back in the shop and it shows 3 pounds and will slowly drop to zero and pull all of the fuel out of the front bowl, so you think vapor lock right? Well that is what it acts like for sure, but its never did it before on hotter days than it is now and I did not change anything. All of a sudden after 3 years it acts up.
540 cubic inch.
clay smith mechanical big block fuel pump. 1000 cfm AED 4150 carb.
1/2 inch steel braided fuel line from the tank to the pump and then 1/2 inch line to the fuel regulator and then 1/4 inch lines to each bowl, they are all wrapped with reflective heat resistant tape, I used the original 3/8 fuel line for the return to the tank. I checked the inline fuel filter and it is good. I have have raced this car in vegas at 100 degrees without a any issue, hot lapping it.
Before I start throwing parts at it I would appreciate some insight from anybody who has seen something similar.
Maybe the fuel pump is giving up but I don't think so because the car will light right up 2 hours later when the fuel bowl fills with 7 pounds on the regulator. Thanks ahead of time for your insight.
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post #2 of 40 (permalink) Old Jun 2nd, 20, 4:41 PM
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Is the tank vented?
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post #3 of 40 (permalink) Old Jun 2nd, 20, 5:35 PM
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Kerry
 
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Re: Maybe vapor lock.

Have you been buying fuel from a different source?

The formulation may have changed, and you are now having the fuel boil. Wrapping the lines and installing the holley 108-70 heat shield eliminated intermittent issues I was having when driving on the street, but almost every run at the track.
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post #4 of 40 (permalink) Old Jun 2nd, 20, 5:55 PM Thread Starter
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Re: Maybe vapor lock.

Quote:
Originally Posted by 67ss4spd View Post
Is the tank vented?
It has the origanal style gas cap on it that is supposed to be vented,
but that does not it did not fail, thats another thing I am going to check.
pretty hard to pull fuel if the tank has vaccum.
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post #5 of 40 (permalink) Old Jun 2nd, 20, 6:08 PM
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Re: Maybe vapor lock.

It can depend on when you bought fuel. Winter blend is a disaster. In June the fuel is much different.

My car struggles in warm temps with Winter fuel plus Im at 6400.
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461" BBC 11.25:1 Compression
840 Rec Heads (2.25/1.88) AED 850 HO carb
Orig Exhaust Manifolds
Straub (Clay Smith) Hyd Roller cam, .050 229/241 .600/.569 109.
TH400, 3500 stall, 4.10 12 bolt posi
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post #6 of 40 (permalink) Old Jun 2nd, 20, 6:09 PM Thread Starter
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Mike
 
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Re: Maybe vapor lock.

Quote:
Originally Posted by pockets View Post
Have you been buying fuel from a different source?

The formulation may have changed, and you are now having the fuel boil. Wrapping the lines and installing the holley 108-70 heat shield eliminated intermittent issues I was having when driving on the street, but almost every run at the track.
Chevron premium fuel, from the same source.
I was also thinking maybe the bowls were boiling from heat.
I pulled it in the shop today and watched the fuel pressure drop from 3 pounds to 0 in about 2 minutes after a high speed run, and also watched the sight glass have fuel in the very bottom and then after 2 minutes the car sucked it dry, and right when the car died I took the fuel line off of the primary bowl on the front and there was no fuel in the line and had my daughter turn it over and and there was no fuel coming out of the line why she is turning it over. So that makes me think fuel pump giving up, but go out there 2 hours later and turn it over and the fuel bowl fills up in about 10 seconds. sheeeesh.
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post #7 of 40 (permalink) Old Jun 2nd, 20, 6:16 PM Thread Starter
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Mike
 
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Re: Maybe vapor lock.

Quote:
Originally Posted by rp930 View Post
It can depend on when you bought fuel. Winter blend is a disaster. In June the fuel is much different.

My car struggles in warm temps with Winter fuel plus Im at 6400.
It has new fuel from yesterday. I am close to that elevation, and have raced at bandermier a handfull of times. so 8500 DA is not new to me, mostly I at Grand Junction.
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post #8 of 40 (permalink) Old Jun 2nd, 20, 6:49 PM
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Greg.
 
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Re: Maybe vapor lock.

Fuel Pump/Regulator are cooler when Engine/Car has sat for a while

After doing your Hot Runs they become Hotter thus they do not work as well

In the 80s I had put a 1/2" Copper Fuel Line on my 65 GTO with just a Stock Fuel Pump
and at the 1,000' Mark on the Track she would fall flat / no Acceleration

Added a Inline Electric Fuel Pump back near the Gas Tank and problem solved

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


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post #9 of 40 (permalink) Old Jun 2nd, 20, 7:26 PM
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Re: Maybe vapor lock.

Dealing with todays fuel is no fun. A return line can help.
Jeff65SS likes this.

461" BBC 11.25:1 Compression
840 Rec Heads (2.25/1.88) AED 850 HO carb
Orig Exhaust Manifolds
Straub (Clay Smith) Hyd Roller cam, .050 229/241 .600/.569 109.
TH400, 3500 stall, 4.10 12 bolt posi
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post #10 of 40 (permalink) Old Jun 2nd, 20, 7:42 PM
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check the fuel pump pushrod, pull it out when you pull pump they can wear and as things heat up clearance might increase
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post #11 of 40 (permalink) Old Jun 2nd, 20, 8:50 PM
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Bill
 
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i have exactly the same fuel pump and 1/2” fuel line but inly a 1/4” return line with a .70 jet. no vapor issues so I doubt thats your issue. I have had issues with regulator diaphram going bad bleeding off pressure thru vent when real hot
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Tremec by Liberty[/FONT]

Foxwell 475 BBC 688hp /610 tq
9.5 cr pump gas Brodix heads by Foxwell Straub hyd Roller
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post #12 of 40 (permalink) Old Jun 2nd, 20, 8:54 PM
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Bill
 
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not sure what year but make sure your fuel tank vent tube not pinched off or collapsed
Assume this a new thing ran well before. mo new underhood heat source

66 CDN Malibu SS A51,L34,M20 Aztec Bronze

Tremec by Liberty[/FONT]

Foxwell 475 BBC 688hp /610 tq
9.5 cr pump gas Brodix heads by Foxwell Straub hyd Roller
Crusin / Track video
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post #13 of 40 (permalink) Old Jun 2nd, 20, 9:46 PM
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Spike
 
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Re: Maybe vapor lock.

Quote:
Originally Posted by Mike 70SS View Post
I feel I am chasing my tail.
I start up the chevelle and it shows 7 pounds fuel pressure on the regulator, go up the road and get it hot with a high speed pass, and pull back in the shop and it shows 3 pounds and will slowly drop to zero and pull all of the fuel out of the front bowl, so you think vapor lock right? Well that is what it acts like for sure, but its never did it before on hotter days than it is now and I did not change anything. All of a sudden after 3 years it acts up.
540 cubic inch. clay smith mechanical big block fuel pump. 1000 cfm AED 4150 carb.
1/2 inch steel braided fuel line from the tank to the pump and then 1/2 inch line to the fuel regulator and then 1/4 inch lines to each bowl, they are all wrapped with reflective heat resistant tape, I used the original 3/8 fuel line for the return to the tank. I checked the inline fuel filter and it is good. I have have raced this car in vegas at 100 degrees without a any issue, hot lapping it. Before I start throwing parts at it I would appreciate some insight from anybody who has seen something similar. Maybe the fuel pump is giving up but I don't think so because the car will light right up 2 hours later when the fuel bowl fills with 7 pounds on the regulator. Thanks ahead of time for your insight.
Hi Mike, I've had similar issues before with my old engine and combo. Be glad yours is a 70, my 69 is the one
with the extra tube in the gas tank so when it was 1/2 to 3/4 full, fuel would be siphoned out of the tank.

I also now have the Clay Smith BBC fuel mechanical fuel pump. When I replace my gas tank with the Tanks, Inc larger tank, I'll use the 3/8 line as a return line. I have a heavy duty continental 1/2 inch I.D. fuel line at the ready.
It's not stainless steel, but a 300 psi heavy duty industrial fuel rated hose.

I bet, if you drive her around and use of the winter fuel, you'll be okay with the summer blend.
But summer blends might not be out as usual, because I bet, with the lack of driving by Americans
during corvid-19 they've got excess stock of winter fuel and don't have room for summer blends
until they sell all the winter fuel.

Oh I don't know if this would help or not, but I'm using one of the clay smith in-line regulators
that are typically used with Enderly Fuel Injection, I have mine at the back end of the carb so fuel
is constantly flowing. Let me link that here: LINK
You can see the brass body underneith the fuel log with the arrow
pointing in the direction of flow. Ideally they say, 1/2inch should be used each way
for best results, but I think it should be okay sending back through 3/8 inch steel line.

Question, aren't the bowls in these carbs suppose to close when the float level is raised?
How are your bowls draining of fuel? Is it sucking it back through? I guess you don't know.

Good luck.

BTW What does your Chevelle run at the strip?
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post #14 of 40 (permalink) Old Jun 2nd, 20, 9:50 PM
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Bill
 
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Thats a good point if in your area still winter gas around

66 CDN Malibu SS A51,L34,M20 Aztec Bronze

Tremec by Liberty[/FONT]

Foxwell 475 BBC 688hp /610 tq
9.5 cr pump gas Brodix heads by Foxwell Straub hyd Roller
Crusin / Track video
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post #15 of 40 (permalink) Old Jun 2nd, 20, 11:04 PM Thread Starter
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Re: Maybe vapor lock.

Quote:
Originally Posted by USMC_Spike View Post
Hi Mike, I've had similar issues before with my old engine and combo. Be glad yours is a 70, my 69 is the one
with the extra tube in the gas tank so when it was 1/2 to 3/4 full, fuel would be siphoned out of the tank.

I also now have the Clay Smith BBC fuel mechanical fuel pump. When I replace my gas tank with the Tanks, Inc larger tank, I'll use the 3/8 line as a return line. I have a heavy duty continental 1/2 inch I.D. fuel line at the ready.
It's not stainless steel, but a 300 psi heavy duty industrial fuel rated hose.

I bet, if you drive her around and use of the winter fuel, you'll be okay with the summer blend.
But summer blends might not be out as usual, because I bet, with the lack of driving by Americans
during corvid-19 they've got excess stock of winter fuel and don't have room for summer blends
until they sell all the winter fuel.

Oh I don't know if this would help or not, but I'm using one of the clay smith in-line regulators
that are typically used with Enderly Fuel Injection, I have mine at the back end of the carb so fuel
is constantly flowing. Let me link that here: LINK
You can see the brass body underneith the fuel log with the arrow
pointing in the direction of flow. Ideally they say, 1/2inch should be used each way
for best results, but I think it should be okay sending back through 3/8 inch steel line.

Question, aren't the bowls in these carbs suppose to close when the float level is raised?
How are your bowls draining of fuel? Is it sucking it back through? I guess you don't know.

Good luck.

BTW What does your Chevelle run at the strip?
I watch it run out as the car is sitting there idling meaning the car is burning it and nothing is coming to the fuel bowl. it basically runs out of fuel with some still in the tank,and an hour later crank it over and the bowl fills quick, its been good for 3 years and all of a sudden it starts this, somthing has changed but I dont know what.
In decent air it goes bottom 10ns at 130mph with a 1.40 60 foot off of a foot brake, fun stuff.
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