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Fuel system configuration/line size (Read 5064 times)
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Fuel system configuration/line size
12/04/11 at 14:54:42
 
I'm going to be ordering tubing for the fuel system in my 73 Javelin. I've done one system in my son's 72 Javelin and I'm thinking of making some changes to what I did for his car. In the 72 I used a 3/8" line from the tank with the pickup and filter sock 3/8" as well. I have a 3/16" return running from a RobbMc fuel pump. We have a hot start issue that seems to be related to the line from the pump to the carb heating up. What I thought might be a better set up is to run the fuel line to the carb wthout a return line until the connector to the carb. A backpressure regulator at the back of the carb and then a return line to the tank seems like the best way to do this.
 Does anyone make a backpressure regulator for this application? This is a street car that may go down the track sometime. I'm shooting for a 401 that makes 400hp. I feel the 3/8" supply will be large enough, but what size should the return be?
 
Dave Z
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Re: Fuel system configuration/line size
Reply #1 - 12/04/11 at 19:00:36
 
What's used instead of a "Regulator" is called a "ByPass Regulator", externally they look the same,
but internally they are different than a "dead head" Regulator.
Another way is a "Fuel Log" with a small changebale "Pill" or "Jet" in the return line outlet.
iirc the Return Line can be smaller than the 3/8 Feed Line.
The stock 5/16 Feed Line is commonly used as the Return Line
after making some plumbing changes at the tank end.
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Re: Fuel system configuration/line size
Reply #2 - 12/04/11 at 19:54:31
 
Phat,
  Thanks for the reply. The "pill" at the end of the fuel log comes close to what I was thinking. What I had in mind was a device that did the same thing but had a diaphram to maintain a preset backpressure and would pass the excess pressure back to the tank. The bypass regulator is the other option and would probably work better than what I had in mind. The fuel log option would be a cleaner install which was one of the things I was looking for.
  In the case of my son's car, do you think that a 3/16" line is too small?
 
Dave Z
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Re: Fuel system configuration/line size
Reply #3 - 12/04/11 at 20:30:36
 
Dave I think the 3/16 would be fine as all you want to do is have a low flow or movement of fuel in ALL lines so you donít have the heat build up. Thought thatís why AMC did the return out of the fuel filter. Also thought it was posted the filter has a restrictor on the return side as not to bleed off too much fuel?
Might find so thing here http://www.barrygrant.com/bgfuel/default.aspx?page=techsupport
I like the pill in the return as it can be adjustable if not sized right the first time Wink
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Re: Fuel system configuration/line size
Reply #4 - 12/06/11 at 00:45:17
 
not from experience, just talking point, if you had a pill and a return line, would think a conventional regulator would control the pressure.  Regulator doesn't know if you have a two barrel or 4 barrel or 6 barrel or a 4 barrel and a return line.  
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Re: Fuel system configuration/line size
Reply #5 - 01/24/12 at 10:02:35
 
 I need to hear from anyone who has ordered a fuel line from Inline Tube for a humpster. Did it fit without issue?
 
Dave Z
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Re: Fuel system configuration/line size
Reply #6 - 05/05/12 at 23:44:55
 
I'm continuing this post instead of starting a new one as they are connected, at least for me. My son's Javelin is having a fuel problem that goes like this:
 
 After running, when the car is parked and turned off gas goes into the secondarys and leaks out the throttle shafts. The secondary bowl fuel level goes down to just under the sight window. The fuel bowls are actually cool to the touch. I have a pressure gauge on the fuel line and pressure goes from 5 psi when running to 0 psi when the engine is turned off. This does not happen if the engine is started but the car is not driven, regardless of what speed and how long the engine is run. If the car is driven the condition will occur, if it's not driven it won't. If the car is started but not driven, the fuel bowls are actually warmer to the touch than when the car is driven. The fuel tank is vented.
 The engine is a 360 with a 770 Holley Ultra Street Avenger on an air gap manifold, I have a RobbMc fuel pump with a 3/16" return line off the pump. I have a 1" aluminum 4 hole to open spacer under the carb. The fuel line from the pump to the carb is insulated, the filter, which is just in front of the carb feels warmer when driven than when just started but not moved. The PCV line is connected to the nipple on the back of the carb. When parked in my driveway, the carb sits dead level front to back.
 
  Any thoughts?
 
Dave Z
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Re: Fuel system configuration/line size
Reply #7 - 05/06/12 at 21:59:51
 
Quote from pipefitter on 05/05/12 at 23:44:55:
I'm continuing this post instead of starting a new one as they are connected, at least for me. My son's Javelin is having a fuel problem that goes like this:

After running, when the car is parked and turned off gas goes into the secondarys and leaks out the throttle shafts. The secondary bowl fuel level goes down to just under the sight window. The fuel bowls are actually cool to the touch. I have a pressure gauge on the fuel line and pressure goes from 5 psi when running to 0 psi when the engine is turned off. This does not happen if the engine is started but the car is not driven, regardless of what speed and how long the engine is run. If the car is driven the condition will occur, if it's not driven it won't. If the car is started but not driven, the fuel bowls are actually warmer to the touch than when the car is driven. The fuel tank is vented.
The engine is a 360 with a 770 Holley Ultra Street Avenger on an air gap manifold, I have a RobbMc fuel pump with a 3/16" return line off the pump. I have a 1" aluminum 4 hole to open spacer under the carb. The fuel line from the pump to the carb is insulated, the filter, which is just in front of the carb feels warmer when driven than when just started but not moved. The PCV line is connected to the nipple on the back of the carb. When parked in my driveway, the carb sits dead level front to back.

†Any thoughts?

Dave Z
Dave the level should be below the window. Remember in the old days we had to pull the screw out of the bowl to check the level it it should be just even or tad below the bottom of the hole. I say lower the level as see what happens. I would also like to know where the fuel is coming from when off that it is leaking into the carb? Is it out the vent tube?
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Re: Fuel system configuration/line size
Reply #8 - 05/06/12 at 22:10:17
 
Quote from pipefitter on 05/05/12 at 23:44:55:
I'm continuing this post instead of starting a new one as they are connected, at least for me. My son's Javelin is having a fuel problem that goes like this:

After running, when the car is parked and turned off gas goes into the secondarys and leaks out the throttle shafts. The secondary bowl fuel level goes down to just under the sight window. The fuel bowls are actually cool to the touch. I have a pressure gauge on the fuel line and pressure goes from 5 psi when running to 0 psi when the engine is turned off. This does not happen if the engine is started but the car is not driven, regardless of what speed and how long the engine is run. If the car is driven the condition will occur, if it's not driven it won't. If the car is started but not driven, the fuel bowls are actually warmer to the touch than when the car is driven. The fuel tank is vented.
The engine is a 360 with a 770 Holley Ultra Street Avenger on an air gap manifold, I have a RobbMc fuel pump with a 3/16" return line off the pump. I have a 1" aluminum 4 hole to open spacer under the carb. The fuel line from the pump to the carb is insulated, the filter, which is just in front of the carb feels warmer when driven than when just started but not moved. The PCV line is connected to the nipple on the back of the carb. When parked in my driveway, the carb sits dead level front to back.

†Any thoughts?

Dave Z
If you think the issue is from heat that spacer would not help to keep the carb from heat soak when off. I would look at a plastic one if you think it is heat related when off to see if that helps.
I think it is a fuel that is too high to start off with.
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Re: Fuel system configuration/line size
Reply #9 - 05/07/12 at 01:13:48
 
Dave,
 On a Holley carb that comes from the factory with a window, the fuel is supposed to be in the window. You're thinking of carbs that have the screw that you take out and the fuel is supposed to be at the bottom of the opening.
 Today I was able to see the gas coming out of the holes in the ventury just above the throttle plates and then turn into a stream of vapor. I don't nessesarily think the source of the heat is the manifold itself as it's an air gap manifold which has no exhaust cross over and has the air gap for cooling. I think the PCV may be contributing to the heat at the carb secondaries.  
 The carb spacer is one that was recomended by Ken Parkman after he did a dyno test of different induction set ups. I really don't want to lose it. I do have room to raise the carb another inch without hitting the hood and I have a 1" aluminum spacer with a nipple on it that I could use as the PCV connection. If I could find a plastic spacer that did the same thing that might be the solution.  
 Unless this is unique to aluminum bodied carbs, a lot of other Holley carbs must have the same issue. Huh
 
Dave Z
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Re: Fuel system configuration/line size
Reply #10 - 05/07/12 at 12:34:03
 
I would lower to level. When the "plastic" windows came out you only used them to set level (to the bottom of the hole) and then put the screw back in as they could melt. They where  made so fuel would not leak all over the intake and make a mess or start a fire. I also say lower the level because if you check the old bowles and the one with the window are they in the same place? What has changed on the inside of the carb that you can run a higher level now? Maybe I am wrong? I do know a little level change can make a big differance in adjustments of the carb. Drag car level was a little low and had a bog, upped the level to the bottom of the hole (I did not think it was that low to start) and it took a lot of the bog out.
I say lower the level as a try and if it still has issues put it back up. This way you can keep the alum. spacer but maybe 2 gaskets on each side of it?
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Re: Fuel system configuration/line size
Reply #11 - 05/07/12 at 21:28:50
 
Dave,
 http://www.holley.com/data/Products/Technical/199R10487-1rev4.pdf
level adjustment is on page 11. It's pretty clear that the fuel should be in the middle of the window.
 
Dave Z
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Re: Fuel system configuration/line size
Reply #12 - 05/07/12 at 22:50:35
 
Yep you are right half window. I do see they use a different window than the screw in type but still looks like it is in the same place on the fuel bowl so as I said before wonder what they changed on the carb to up the level and not cause issues with too high of a level?
 
Might be time to call Holley to find out why the fuel leaks in when off. Bad gasket or plugged jet some where? Maybe ask why the higher level now too? I dont know where any of my Holley books are to see if I can see here the fuel is coming out so that system could be checked more closely for issues, sorry.
I still think for S & G I would lower it to old school level just to see what happens. Little time and tools and could be all fixed? If not put it back Smiley
Good luck and keep us posted when you get it fixed
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Re: Fuel system configuration/line size
Reply #13 - 05/08/12 at 00:31:15
 
I tried a few things tonight. First I moved the PCV connection to a nipple on the front of the carb. No difference.
 I took the secondary bowl off. The first picture shows the hole where fuel goes into the ventury when the engine is turned off. It happens on both sides.

The next two are just additional pictures.


The last picture didn't focus on the bowl but I think you can still see there is a difference between where the sight glass is and where the boss for the level plug is.
I hate to just lower the fuel in the bowl as I think that would mask a symptom and not fix the problem.
 
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Re: Fuel system configuration/line size
Reply #14 - 05/08/12 at 03:43:43
 
Maybe I should of asked this before, Is that carb new or rebuilt and if rebuilt are you sure the right gaskets where used?
All the gasket came off too clean to be new even with the new blue gaskets all be it they are better not to stick.
I know you said this happens if motor is run but not driven but does not happen went driven. Is this with and with out a filter on?
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