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| | | | Joined: May 2005 Posts: 1,624 Shop Shark | | Shop Shark Joined: May 2005 Posts: 1,624 | If one were to mistakenly put a non vented gas cap on a truck which required one what would the symptoms be? This truck has an aftermarket gas cap which was not tightened enough to get it to vent. It is spring loaded and we are unsure if it was venting the tank. The truck, after getting hot will buck and stumble through half petal but run good on full petal. Could this be the cap?
Last edited by beltfed; 02/28/2017 3:15 AM.
Six volt guy living in a twelve volt world
| | | | | Joined: Oct 2006 Posts: 843 Shop Shark | | Shop Shark Joined: Oct 2006 Posts: 843 | A non-vented cap will stall the engine. As the fuel is pulled out of the tank,air can't get in. Therefore a vacuum is created. The fuel pump can't overcome the vacuum,hence the engine will stall. Depending on how much fuel is in the tank will determine when it will stall.
| | | | | Joined: Feb 2004 Posts: 29,841 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,841 | The truck, after getting hot will buck and stumble through half petal but run good on full petal. Could this be the cap? Try loosening or removing the cap and see if the symptoms persist. Another check involves disconnecting the vacuum advance to see if maybe a wire inside or near the distributor has broken strands that only show up at certain positions of the vacuum chamber. I've seen that one repeatedly. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Sep 2011 Posts: 1,458 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,458 | Have seen more than one fuel tank sucked in by fuel pump due to no / blocked vent.
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: May 2005 Posts: 8,983 Sir Searchalot | | Sir Searchalot Joined: May 2005 Posts: 8,983 | As said, when stumbling, jump out and take the cap off, take it into the truck and drive off and see how it acts.
You can buy ten caps and those cheap sons-a-guns won't vent.....or you can buy one and simply drill a 1/16-3/32 hole near center and be happy.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
| | | | | Joined: Oct 2006 Posts: 843 Shop Shark | | Shop Shark Joined: Oct 2006 Posts: 843 | What puzzles me is you said it will run good at full throttle. A venting issue should be a constant. | | | | | Joined: May 2005 Posts: 8,983 Sir Searchalot | | Sir Searchalot Joined: May 2005 Posts: 8,983 | Very possibly true, but he asked if it could be the cap and we are advising how to eliminate it as a cause of stumble. When he asks for help on whatever issue it has and provides total history and description, we will know more.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
| | | | | Joined: May 2005 Posts: 1,624 Shop Shark | | Shop Shark Joined: May 2005 Posts: 1,624 | BC52, That's what has me puzzled. Truck is in the hands of my nephew now and he has complained about it missing, bucking until you put your foot into it with engine warmed up. He filled it with gas several days ago and noticed that the after market keyed gas cap was not being turned completely clockwise. He did so and truck ran fine. He is coveniced (not me) that the gas cap was not letting the tank vent thus causing the problem. That's why I ask such a strange question to start with.
Six volt guy living in a twelve volt world
| | | | | Joined: May 2005 Posts: 8,983 Sir Searchalot | | Sir Searchalot Joined: May 2005 Posts: 8,983 | Could be the cap and could be the rejuvinated gas and could be something else. Won't know unless it happens again. But nice to hear it's OK now.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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