Gas Cap Question
Thread Starter
Le Mans Master
Joined: Apr 2000
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From: New York New York
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Gas Cap Question
My friend has a true 70 LT-1. I was setting his back float with the engine running and as I was adjusting it the fuel started to come out the sight hole too fast.
So I told him to shut it off so I can check the needle and seat.
Gas started to pour out the sight hole and when I put my finger over the hole, fuel started to come out the boost venturies and was filling up the rear barrels!
I told him to loosen the gas cap and the fuel slowed down and finally stopped.
Here is my question:
He has the proper fuel tank w/o EEC and a two line fuel pump.
Should he have a vented or non-vented cap with this setup?
He has the non vented cap on there now and I believe it should be vented.
It was a very warm day and he had the car out for quite a while.
Thanks,
Joe
So I told him to shut it off so I can check the needle and seat.
Gas started to pour out the sight hole and when I put my finger over the hole, fuel started to come out the boost venturies and was filling up the rear barrels!
I told him to loosen the gas cap and the fuel slowed down and finally stopped.
Here is my question:
He has the proper fuel tank w/o EEC and a two line fuel pump.
Should he have a vented or non-vented cap with this setup?
He has the non vented cap on there now and I believe it should be vented.
It was a very warm day and he had the car out for quite a while.
Thanks,
Joe
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
i believe the older cars need the vented one, because the dont have the fuel vapor cannister.
http://www.zip-products.com/Zip/prod...951879FA539961
http://www.zip-products.com/Zip/prod...951879FA539961
Team Owner
Joined: Sep 2006
Posts: 31,214
Likes: 4,302
From: Westminster Maryland
Hi Joe,
By 2 lines do you mean a supply and return both on the passegers side frame rail, or a supply on the passengers side and a vapor line on the driver's side? 70 LT-1s had just 1 supply line and had a vapor line ONLY if they had the NA9 (EEC) option. 70 caps were all sealed.
Regards,
Alan
By 2 lines do you mean a supply and return both on the passegers side frame rail, or a supply on the passengers side and a vapor line on the driver's side? 70 LT-1s had just 1 supply line and had a vapor line ONLY if they had the NA9 (EEC) option. 70 caps were all sealed.
Regards,
Alan
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
70's came with vent lines and non-vented gas caps. However, lots of changes can occur over 35+ years of operation. The cap needs to be selected based on how the car is configured now...not on how it was configured from the factory.
Team Owner
Joined: Sep 2006
Posts: 31,214
Likes: 4,302
From: Westminster Maryland
Hi 7T1,
I understand your point. I asked my question because Joe said he was working on a 'TRUE' 70 / LT-1. I was curious what configuraion he was seeing. I didn't think he was seeing 2 lines on the passenger side frame rail because that would mean the fuel pump, and the tank had been changed too, or it wasn't an original 70 / LT-1.
You'll notice I only reply to posts about originally configured cars since that's the only knowledge I have. Just trying to understand a 38 year old car.
If I had a dollar for every 70-72 made-up LT-1 I've seen I'd buy each of us a case of our favorite adult beverage.
Regards,
Alan
I understand your point. I asked my question because Joe said he was working on a 'TRUE' 70 / LT-1. I was curious what configuraion he was seeing. I didn't think he was seeing 2 lines on the passenger side frame rail because that would mean the fuel pump, and the tank had been changed too, or it wasn't an original 70 / LT-1.
You'll notice I only reply to posts about originally configured cars since that's the only knowledge I have. Just trying to understand a 38 year old car.
If I had a dollar for every 70-72 made-up LT-1 I've seen I'd buy each of us a case of our favorite adult beverage.
Regards,
Alan
Race Director
Joined: Oct 2000
Posts: 12,657
Likes: 3,117
From: Shamong, NJ
All 70-74's originally used a sealed gas cap. The markings and configuration of the 70 cap was different than the 71, and the 71 was slightly different than the 72-74 cap.
If I remember correctly, 70-72 LT-1's, with the Holley, all had a 2 line system (fuel line and a return line). Quadrajet cars (350 & 454) had a 3 line system. The LT-1 uses a different fuel tank than the Corvettes with the other engines also.
If I remember correctly, 70-72 LT-1's, with the Holley, all had a 2 line system (fuel line and a return line). Quadrajet cars (350 & 454) had a 3 line system. The LT-1 uses a different fuel tank than the Corvettes with the other engines also.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
It sounds like there was some debris holding the secondary needle/seat open.
Regardless of the cap configuration, the needle and seat assembly should be able to stop the flow of fuel to at least 8 psi. If you ever had that much pressure in your fuel tank, it would probably rupture the tank well before 8 psi.
Regardless of the cap configuration, the needle and seat assembly should be able to stop the flow of fuel to at least 8 psi. If you ever had that much pressure in your fuel tank, it would probably rupture the tank well before 8 psi.
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Thread Starter
Le Mans Master
Joined: Apr 2000
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From: New York New York
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Alan 71, I mean by two line pump is that it has only has an inlet and outlet.
There is no return line to the tank. There is only one 3/8 line on the chassis rail.
Does the tank have a vent line on it or should the cap be vented?
To keep you updated, I went over his house today and when I removed the rear needle/seat assembly there was metal filings on the seat.
So I looked at the bowl and the threads are gone.
I will replace the bowl and go from there.
Thanks,
Joe
There is no return line to the tank. There is only one 3/8 line on the chassis rail.
Does the tank have a vent line on it or should the cap be vented?
To keep you updated, I went over his house today and when I removed the rear needle/seat assembly there was metal filings on the seat.
So I looked at the bowl and the threads are gone.
I will replace the bowl and go from there.
Thanks,
Joe
Team Owner
Joined: Sep 2006
Posts: 31,214
Likes: 4,302
From: Westminster Maryland
Hi Joe,
Well that's good news, at least you have a 'culprit' now!
I believe a 70 LT-1 has 1 supply line as you've said. It has no vapor/EEC line on the driver's side frame rail UNLESS it was a California delivery with NA9.
The gas caps, 68-72, were the sealed type. All tanks have a little round 'relief valve' on top of the tank.
Regards,
Alan
You can just see the valve in the upper right corner near the filler neck.
This picture also shows the EEC valve mount and hose nipple on the right side of the tank
Well that's good news, at least you have a 'culprit' now!
I believe a 70 LT-1 has 1 supply line as you've said. It has no vapor/EEC line on the driver's side frame rail UNLESS it was a California delivery with NA9.
The gas caps, 68-72, were the sealed type. All tanks have a little round 'relief valve' on top of the tank.
Regards,
Alan
You can just see the valve in the upper right corner near the filler neck.
This picture also shows the EEC valve mount and hose nipple on the right side of the tank
Last edited by Alan 71; Jul 28, 2008 at 06:35 PM.