Too much gas tank pressure! - Team Camaro Tech
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post #1 of 10 (permalink) Old Jun 15th, 01, 11:41 AM Thread Starter
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Chris
 
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I've got a 330hp/350 GM crate with a Holley 750 vac sec. I'm thinking it may be too much for this motor as it still runs rich with mixture leaned back to nearly 1/2 turn out! I was just now putting a 625 holley on and when I disconnected the fuel line....It sprayed like a garden hose all over the place. I quickly put my thumb over the line and yelled for my wife to take off the gas cap...When she did, the sudden release of pressure blew the cap off so hard it hit her in the face! That can't be normal. ONly about 1/8th of a tank of gas. Could this much pressure be affecting performance? Perhaps forcing too much fuel through the carb? Still unclear as to why there seems to be more pressure with less gas in the tank than with the tank nearly full. Any comments, advice would be greatly appreciated!

By the way, my wife's black eye should heal just fine.

Kidding!
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post #2 of 10 (permalink) Old Jun 15th, 01, 01:07 PM
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That 750 should work fine.
If you have the factory crossflow muffler, check for an exhaust leak. I had hot exhaust gas blowing on my gas tank, causing it to boil the fuel!
It will get worse when the tank is low.
Also get the gas cap tested.
The smog test places in Calif, test the cap for the amount of pressure it can hold back.

I asked the guy how much pressure it was, and he didn't know! the guage just reads PASS/FAIL.
I would guess your fuel cap should not allow the tank pressure to go over 6 to 7 psi. as the carb would not be able to handle more than that.
David

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[This message has been edited by davidpozzi (edited 06-15-2001).]
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post #3 of 10 (permalink) Old Jun 16th, 01, 04:09 AM Thread Starter
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Thanks Dave. It sure seemed like there was more than 6-7 psi of pressure in there. I heard the thing blow off from the front of the car. Do you think there would be a problem with drilling a small hole in the gas cap to relieve the pressure? I'm thinking that it is the fuel pump's job to deliver all the required fuel under pressure, not the tank's!
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post #4 of 10 (permalink) Old Jun 16th, 01, 05:43 AM
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Mine does it too, but not to the extent that you are describing. It was funny though when I was swapping out my carb... I unhooked the line and it was definately gushing gasoline everywhere until I popped the cap. You can buy venting gas caps from Rick's First Generation.
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post #5 of 10 (permalink) Old Jun 16th, 01, 07:41 AM
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The newer fuels have oxigenates in them and stuff like ether, this makes for some nasty fumes coming out of the gas tank.
You should maintain some pressure on the tank to keep these fumes from escaping or your fuel will go sour faster when the car is stored, there will be more danger of fire or explosion if you park in a garage, due to the fumes.

I was thinking about why it would be worse when the tank is low...
A near empty tank would have more volume of compressed air/fumes in it, so it would "feel" like there was more pressure due to the larger volume escaping when the cap was released.
If it isn't over 6 psi or so, it's OK as is.

I'd buy a new cap.
David

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67 RS 327
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65 Lola T-70 Chev 350 Can-Am Vintage Racer

[This message has been edited by davidpozzi (edited 06-16-2001).]
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post #6 of 10 (permalink) Old Jun 23rd, 01, 07:02 PM
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Hey englemac, I see you made it to N.C.....
How are things at Pope AFB? Where did you find a place to live? Are you planning on going to any car shows in the southeast?


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post #7 of 10 (permalink) Old Jun 24th, 01, 01:11 AM
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Drilling a hole in the cap is addressing the symptom, not the problem. When I remove my cap there is sometimes the slightest hiss. I would suspect heat causing the volume of air/fumes to expand.Please let us know how it resolves itself.

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post #8 of 10 (permalink) Old Jun 24th, 01, 04:12 AM
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You don't say what year car you have. 67-9 Camaro's use vented gas caps. Is yours a vented cap ? It will say so on the cap.
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post #9 of 10 (permalink) Old Jun 24th, 01, 12:21 PM Thread Starter
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Hey Bob!yeah..finally made it here to Fayetteville, NC. Got a decent place to stay in this not so decent town. 50,000+ Army and 3000+ AF rightfully earned this town the nickname "Fayette-nam". I've been trying to find some car shows local, but the funny thing is - this is the first place where I can't find any car shows and cruises. And old cars are more rare than usual.

As for the gas tank, I drilled a tiny hole in the cap until I can find a more permanent solution. I didn't want to crack the filler neck like my last tank. My cap says it is vented, but didn't seem to be venting. I have to take my tank off soon anyway...My guage is reading erratically and off scale high. As far as aircraft go...when a guage reads off scale high, it's trouble! Electric in the fuel tank. I guess the same would hold true for cars.

Oh, Clill...sorry, it is a 69.
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post #10 of 10 (permalink) Old Jun 25th, 01, 08:02 AM
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My buddy once bought a Corvette ZR-1, that was previously totaled and fixed (rollover) He was having performance related problems, it turned out that his gascap had paint dust blocking the vent hole. He fixed it with an old guitar string. the difference in performance was night and day.
John
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