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#1 |
Senior Member
![]() Join Date: Oct 2001
Location: Lancaster S.C.
Posts: 4,752
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what is the cause and cure??
If I let the 69 set for a week in the shop the fuel back feeds out of the fuel line and clear filter back to the fuel pump, not going into the crankcase or anything like that. To get it to crank I have to remove the gas cap and prime the carb. I have never seen this before. Have any of you?
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Things happen for a reason! |
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#2 |
Cluster King
![]() Join Date: Nov 2012
Location: Junction City, OR
Posts: 5,263
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Re: what is the cause and cure??
That is a little bit strange. What type of fuel filter are you using. Some of the inlines have a check valve that only lets fuel go in one direction.
The strange thing is that there should be enough fuel in the float bowl to get the engine to light even if the fuel line is empty. It may not stay running for long but it should start. What carb? It is possible that the float bowl is draining fuel through the base and into the intake. You also need to have a vented cap if you don't already or some way to vent the fuel tank. |
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#3 |
Registered User
Join Date: Dec 2011
Location: Attica,indiana
Posts: 264
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Re: what is the cause and cure??
by chance does it have a quadrajet carb on it ? If it does the primary well could be leaking and causing your problem.
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#4 |
Registered User
Join Date: Jul 2012
Location: Marshall, NC....heart of the Appalachians.....aka, Gods country!!
Posts: 537
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Re: what is the cause and cure??
have the same problem with an edelbrock carb, usually about 2 week sit time, then have to prime to avoid running the battery down cranking so long. Have a carter fuel pump, some -6an lines, a Russell fuel filter with no check valve. Been wondering the same thing and how to fix it?
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#5 | ||
Registered User
![]() Join Date: Dec 2012
Location: Chandler AZ
Posts: 1,149
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Re: what is the cause and cure??
Quote:
Quote:
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1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9 |
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#6 |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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Mechanical pump has a diaphragm in it doesn't? Could be leaking back through it.
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 ![]() Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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#7 |
Account Suspended
Join Date: Jan 2009
Location: Kuna, Idaho
Posts: 1,046
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Re: what is the cause and cure??
I have the same problem with my truck. It has a 650 double pump holley, pressure gauge, and a new clear fuel filter. I have to pour a bit of gas in the carb about 2-3 times before gas actually gets pumped all the way too the carb. While doing all that, I leave my gas cap off, because for some reason the gas tank builds up a lot of pressure.
I never had this problem with my other truck and the longest it sat was 4 months without being started and then fired right up. Its pretty embarrassing having to do this every time with some neighbors that like to watch me cause the truck is really loud. Anyways, hoping someone can find a cure to this ongoing problem. |
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#8 |
Proprietor of Dale's Corner
![]() Join Date: Nov 2012
Location: Vacaville , CA
Posts: 16,103
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Re: what is the cause and cure??
I think it's your fuel pump it has a valve to keep from bleeding back and its not doing its job
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"Some Days Chickens And Some Days Feathers" Dale XNGH ECV Sam Brannan 1004 R.I.P. 67ChevyRedneck R.I.P. Grumpy Old Man |
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#9 |
Senior Member
![]() Join Date: Oct 2001
Location: Lancaster S.C.
Posts: 4,752
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Re: what is the cause and cure??
Well I see I'm not the only one with this issue, The complete fuel system is new and yes to the edelbrock carb also. I'm gonna change the fuel filter out and see if that helps. Ya let me know what you guy's do also, maybe together w can figure this out, check back w yall in a few days w a update!
Thanks Donnie
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Things happen for a reason! |
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#10 | |
Registered User
Join Date: Jul 2007
Location: Toppenish, WA
Posts: 15,506
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Re: what is the cause and cure??
Quote:
As far as Cap goes, if the cap isn't venting it will create a vacuum just as MagmaJct suggested. I had a lot of trouble getting a properly vented cap for one vehicle I had and went through three top brand caps before getting one that worked. The pressure you experience is from the sides of the tank popping back out in place after being sucked in by the vacuum of the fuel pump. The only way the tank in these trucks would build pressure in the tank is if you had the truck sitting out in the hot sun for a length of time and the heat vaporized the gas enough so that it built up vapor pressure in the tank, but then you wouldn't have a starting problem as the pressure would push fuel up the fuel line to the carb most likely.
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Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around. |
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#11 |
Registered User
Join Date: Jun 2010
Location: Denham Springs, La.
Posts: 257
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Re: what is the cause and cure??
Yep, fuel pump. Mine did it until I changed it, now it never does it.
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05 QSM GTO - M6, Corsa, King Springs 70 SWB CST - 350/Auto, Foose 18/17 I upset whiners too.... |
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#12 |
Registered User
Join Date: Jun 2012
Posts: 1,089
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Re: what is the cause and cure??
My 70 does this as well, it has a edelbrock on it. Its a pain if it sets more then 3/4 days.
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#13 |
Registered User
Join Date: May 2008
Location: Mesa, AZ
Posts: 281
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Re: what is the cause and cure??
To the OP and others...
My understanding is that the gas cap is designed to allow vacuum to pull air into the tank to allow for fuel consumption. If the tank is collapsing under vacuum with the engine running/driving, you may have to look into a new cap. As far as the tank pressurizing, this is probably an issue with the evap system being disabled. I have a Carter AFB (Edelbrock 1405 with the electric choke kit installed) that is tough to start if left sitting more than a week. I suspect the fuel in the float bowl is evaporating. These carbs were not designed to reduce emissions.
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I own 3 classic vehicles. 1971 LWB C10 Deluxe. 1974 VW Super Beetle. 1971 VW Fastback. The C10 and the Super Beetle run, the Fastback is just not there yet! Please visit my Super Beetle and Fastback profile on TheSamba. |
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#14 | |
Registered User
Join Date: Feb 2009
Location: southeasternfoothillsofusa
Posts: 1,557
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Sam |
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#15 |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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Just another thought.
Donnie since you mentioned you had to take the cap off and vent the tank it maybe that the tank is sucking the gas back into the tank after sitting like the coolant in the recovery tank. Have u tried leaving the gas cap off when you park it to see what it does? I had a old Chevy Luv truck that I had to take the vent line loose to get to run if it was less than a 1/2 tank. It was pulling so much vacume it would kill the engine. ![]() ![]()
__________________
1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 ![]() Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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#16 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,940
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Re: what is the cause and cure??
Get a vented gas cap... your '69 originally came with one, but someone could have replaced it with a non-vented cap over the years.
Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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