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bug-nuts
Samba Member
Joined: April 30, 2008
Posts: 85
Location: S.E. Kansas
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 Posted: Thu Sep 25, 2008 1:38 pm Post subject: fuel pressure for a Weber carb? |
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I bought my first bus awhile back (1978 Westfalia that the PO changed to a single Weber carb) and am slowly getting it road ready. I'm going to change the fuel lines, add a pressure regulator and try to get the carb. Adjusted this weekend. It has an electric fuel pump but I don't know if it's the OG or a replacement.
What should I set the pressure at for a carburetor, and do I need high pressure fuel line if I add the regulator directly after the pump? Reading about all the fires has me spooked, are these fuel line failures caused by the pressure, the heat or a combination of both? It seems like the fuel line available at most parts stores are rated for a pretty high temperature range but I don’t know at what pressure. I’m guessing the carb. Will only need 6-8 psi, and if so can I use standard fuel line?
Thanks,
Ken
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1973 Thing
1978 Westy
1998 Beetle |
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VDubTech
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Joined: December 29, 2002
Posts: 9152
Location: Syracuse, NY
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| Posted: Thu Sep 25, 2008 1:43 pm Post subject: |
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| Carb only needs about 3.5 psi max. Fires are caused by old, dry rotted fuel lines coming apart and spewing fuel all over hot engine components and/or engine components that spark (coil/distributor). Anything you can buy at your local FLAPS isn't the right stuff to use on your Bus. The fuel line is metric and very few places have it. German Supply carries a kit with all necessary lines already cut to fit and ready to roll. I would get it runnin and get the proper fuel injection back on that engine. The difference will be night and day. |
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Wildthings
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Joined: March 13, 2005
Posts: 52121
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| Posted: Thu Sep 25, 2008 1:45 pm Post subject: |
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| Your fuel pump should say on it somewhere what the output pressure is. You only need 4psi or so to feed the carb. Any new rubber fuel line should do you well enough for starters, but running as much rigid steel as you can and using SS braided AN line elsewhere will give you and extra margin of safety. |
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Randy in Maine
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Joined: August 03, 2003
Posts: 34890
Location: The Beach
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| Posted: Thu Sep 25, 2008 1:47 pm Post subject: |
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You want your fuel pressure to be about 2.5-3.5 psi. Most $20 vacuum gauges will be able to check it.
Fuel lines just get tired and like to crack and split. It may have something to do with the fuel or the quality of the hose, but change them all out about ever 3-5 years so that you can sleep well at night. Use the good clamps that do not cut into the hose. A good grommet will also help keep the hose from getting chafed as it runs through the metal.
Regular fuel line will work in your application due to the low PSI involved, but nothing wrong with 7mm FI hose either if it fits this application.
Been here?
http://www.germansupply.com/home/customer/product.php?productid=17280&cat=300&page=4 |
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Oil Phil-M
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Joined: October 08, 2005
Posts: 543
Location: Vancouver, BC
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| Posted: Thu Sep 25, 2008 5:45 pm Post subject: |
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| I have dual IDFs with a mechanical fuel pressure gauge permanantly mounted on one of the carb fuel line inlets. Set my pressure regulator at 1.5psi. I find after I stop the vehicle the fuel must soak up the heat and expand cuz after 5 -10 minutes the psi will go over the 3.5 recommended max. |
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bug-nuts
Samba Member
Joined: April 30, 2008
Posts: 85
Location: S.E. Kansas
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| Posted: Fri Sep 26, 2008 5:33 am Post subject: |
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| Oil Phil-M wrote: |
| I have dual IDFs with a mechanical fuel pressure gauge permanantly mounted on one of the carb fuel line inlets. Set my pressure regulator at 1.5psi. I find after I stop the vehicle the fuel must soak up the heat and expand cuz after 5 -10 minutes the psi will go over the 3.5 recommended max. |
I plan on using one with a bypass back to the tank which will keep this from happening.
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Whoever smelt it, dealt it.
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1978 Westy
1998 Beetle |
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Oil Phil-M
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Joined: October 08, 2005
Posts: 543
Location: Vancouver, BC
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| Posted: Sat Sep 27, 2008 10:00 am Post subject: |
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| Quote: |
| I plan on using one with a bypass back to the tank |
How and where do you run the return line? Can you tee off the pump outlet line and feed it back to the inlet side of the pump so any excess pressure can flow back into the tank or will that just give you zero fuel pressure?
I think I could have used one of the outlets on the holley regulator as a return line. Instead I chose to install it in the engine bay as high up as possible as a means to curb gravitational gas flow out of the tank. I wasn't sure how i would run a return gas line from inside the engine bay so I used the two outlets as a tee for each of the carbs.
The pump itself is suppose to only produce 4psi so I didn't think excess pressure would be an issue but I didn't realize how much effect heat has on increasing the pressure in the line. |
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Oil Phil-M
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Joined: October 08, 2005
Posts: 543
Location: Vancouver, BC
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| Posted: Sat Sep 27, 2008 10:00 am Post subject: |
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| Quote: |
| I plan on using one with a bypass back to the tank |
How and where do you run the return line? Can you tee off the pump outlet line and feed it back to the inlet side of the pump so any excess pressure can flow back into the tank or will that just give you zero fuel pressure?
I think I could have used one of the outlets on the holley regulator as a return line. Instead I chose to install it in the engine bay as high up as possible as a means to curb gravitational gas flow out of the tank. I wasn't sure how i would run a return gas line from inside the engine bay so I used the two outlets as a tee for each of the carbs.
The pump itself is suppose to only produce 4psi so I didn't think excess pressure would be an issue but I didn't realize how much effect heat has on increasing the pressure in the line. |
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bug-nuts
Samba Member
Joined: April 30, 2008
Posts: 85
Location: S.E. Kansas
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| Posted: Sat Sep 27, 2008 11:37 am Post subject: |
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| Oil Phil-M wrote: |
| Quote: |
| I plan on using one with a bypass back to the tank |
How and where do you run the return line? Can you tee off the pump outlet line and feed it back to the inlet side of the pump so any excess pressure can flow back into the tank or will that just give you zero fuel pressure?
I think I could have used one of the outlets on the holley regulator as a return line. Instead I chose to install it in the engine bay as high up as possible as a means to curb gravitational gas flow out of the tank. I wasn't sure how i would run a return gas line from inside the engine bay so I used the two outlets as a tee for each of the carbs.
The pump itself is suppose to only produce 4psi so I didn't think excess pressure would be an issue but I didn't realize how much effect heat has on increasing the pressure in the line. |
I've not looked specifically into the VW system yet, but I have never seen a fuel system with an electric pump that did not have a return line back to the tank. As far as a mechnical pump, I've seen some with a return line and some without.
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1978 Westy
1998 Beetle |
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Wildthings
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Joined: March 13, 2005
Posts: 52121
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| Posted: Sat Sep 27, 2008 11:46 am Post subject: |
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| Low pressure pumps for use with carburetors typically do not need a return line to the tank. The return line is for cooling the pump which is needed if you are pumping a large volume of excess fuel at high pressures for a FI system. |
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Oil Phil-M
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Joined: October 08, 2005
Posts: 543
Location: Vancouver, BC
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| Posted: Mon Sep 29, 2008 10:01 am Post subject: |
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| I was mistaken with my regulator, there is no by-pass return outlet option. It is available but its on a different regulator that is in the 4-8psi range which is no good. No return line option on the fuel pump I have either so I guess I'm leaving things the way they are. |
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