 Gas tank ventilation, fuel pressure issue |
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| ice cold |
 Jun 28 2014, 09:18 AM
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#1
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Member  Group: Members Posts: 90 Joined: 12-February 14 From: West Palm Beach Florida Member No.: 16,993 Region Association: South East States  |
My 914 loses fuel pressure after running for a while. I have put a pressure guage at the carburators and see the pressure dropping from 3 psi to zero. Does the fuel tank need to be ventilated on a 76 914 when running carbs? I have changed the fuel lines including the line through the tunnel. If ventilation is needed any suggestions on how to best do it. I have pulled the pick up screen and the fuel pump is a 3 1/2 psi pump from cb performance
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Replies(1 - 6)
| Mike Bellis |
Jun 28 2014, 09:32 AM
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#2
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None 
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QUOTE(ice cold @ Jun 28 2014, 08:18 AM)  My 914 loses fuel pressure after running for a while. I have put a pressure guage at the carburators and see the pressure dropping from 3 psi to zero. Does the fuel tank need to be ventilated on a 76 914 when running carbs? With the fuel cap off the car doesn't appear to lose pressure. I have changed the fuel lines including the line through the tunnel. If ventilation is needed any suggestions on how to best do it. Fuel tanks always need to be vented. Always! You should have a vent near the cap that goes into the expansion tank. The expansion tank connects to the charcoal canister. |
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| Cap'n Krusty |
Jun 28 2014, 09:34 AM
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#3
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Cap'n Krusty Group: Members Posts: 10,794 Joined: 24-June 04 From: Santa Maria, CA Member No.: 2,246 Region Association: Central California |
...........and the charcoal canister is connected to both the fan shroud and the air cleaner, providing air flow to remove vapor and burn it.
The Cap'n |
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| ice cold |
Jun 28 2014, 09:51 AM
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#4
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Member Group: Members Posts: 90 Joined: 12-February 14 From: West Palm Beach Florida Member No.: 16,993 Region Association: South East States |
I purchased the car several months ago. There are the two fitting on the bottom of the tank for supply and return. Just checked and you are correct the expansion tank is ventilated. Next step will to be pulling and checking the fuel pump outside of the car.
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| stugray |
Jun 28 2014, 11:56 AM
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#5
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Advanced Member Group: Members Posts: 3,824 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
Does it keep running if you leave the gas tank cap off?
On my Ghia, I had a case where debris in the tank was causing exactly the same symptoms you are describing. However these tanks have a sock around the fuel pickup, so that is far less likely (assuming you still HAVE a sock in the tank.) |
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| SirAndy |
Jun 28 2014, 12:26 PM
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#6
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Resident German Group: Admin Posts: 41,641 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
QUOTE(ice cold @ Jun 28 2014, 08:51 AM) I purchased the car several months ago. There are the two fitting on the bottom of the tank for supply and return. Just checked and you are correct the expansion tank is ventilated. Next step will to be pulling and checking the fuel pump outside of the car. Since this has been converted to a carb setup, did someone plug the air hoses that go from the charcoal canister all the way back to the air-cleaner? If so, they plugged the tank ventilation shut! (IMG:style_emoticons/default/idea.gif) |
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| jvmarino |
Jun 28 2014, 12:52 PM
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#7
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Member Group: Members Posts: 81 Joined: 22-March 09 From: Baltimore Member No.: 10,188 Region Association: None |
Sounds like the small vent line is plugged (ask me how I know). I had driven my carbed car for many years with no problem, but one day after driving around most of the day,the car started sputtering. Pulled off road and started checking all sorts of things, and eventually thought to open gas cap in case my level gauge was just reading wrong. When I unscrewed the cap, lots of whooshing sounds and popping of tank metal as the vacuum was released in the tank.
I had plugged the return and vent lines back at the firewall when restoring the car. After doing some research, realized the gas tank cap does not relieve for vacuum, and I then installed a small one-way valve on vent line at the firewall. No problems since, even after driving car for 4 hours on highway. |
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