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Fuel system configuration/line size (Read 5106 times)
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Re: Fuel system/line size/fuel boils at carb
Reply #15 - 05/13/12 at 11:49:52
 
So I've tried a few things. Since the problem presents itself as fuel leaking at the secondary throttle shaft, I tried feeding the carb from the secondary end instead of the primary end. That way fuel will always flow past the secondary bowl feed to get to the primary bowl. Well, that didn't help.  
 Then I tried opening the secondary plates at idle just a crack to get more fuel to cycle through the secondary bowl. I had to take the carb off the engine to make the adjustment, seemed to pick up idle rpm about 100 rpm. Still the same problem.
 Checking temps some more (by feel), the carb bowls are cool, the carb base feels cool, but the intake is hot, at least when the carb is leaking. I think what's happening is everything is fine when the engine is running and flowing air and fuel, but when shut down, the heat travels quickly through all the aluminum and boils the fuel in the carb. I see the effect at the secondary shaft, I think if I opened the secondary idle more I might not see the leak, but the problem would still be there, and the idle speed would be too high. This engine has always had a hot start issue.
 The carb spacer I have is made by HVH, and they offer the same design in a plastic material, but it's not recomended for street use. Anyone know why?
 
 Dave, this is a new carb and the car doesn't get driven without the filter on. The gaskets are correct as they match correctly with the openings in the metering plate. I tried to buy quality components and feel it's cheaper to buy stuff once and avoid trouble. I guess that doesn't always work.
 
Dave Z
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Re: Fuel system configuration/line size
Reply #16 - 05/13/12 at 15:13:38
 
It sounds like you have everything right. On the plastic spacer they may found it warps or melts because on the street the temps under hood are higher than at the track. You get the motor up to temp in the lanes, make a pass then pit and open the hood to cool down for the next pass in an hour or more.
 
I still say for S&G lower the level, I know thay say it should be half way on the glass, but I do not see what has changed with the carbs that they can up the level and not have a issues with something else.
If yo ulower it and it fixes the shut down / boil but causes something else sneak up on the level till you can live with it.
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Re: Fuel system configuration/line size
Reply #17 - 05/19/12 at 01:15:34
 
 Well I'm still at it. I tried feeding the carb from the back side so fuel has to pass by the seconary side to get to the primary bowl. My thought was less fuel sitting in the carb connector not flowing. That didn't help.
  I tried adding a phenolic spacer to insulate the carb, that didn't help.
 
  I even tried lowering the fuel level in the secondary bowl to the bottom of the window, that didn't help.  
 
  Maybe a sledge hammer?
 
Quote from FuzzFace2 on 05/13/12 at 15:13:38:

I still say for S&G lower the level, I know thay say it should be half way on the glass, but I do not see what has changed with the carbs that they can up the level and not have a issues with something else.
Dave ----

Dave, The window in the bowl is lower than if the carb had come with a screw that gets removed to set the float height, Holley didn't raise the fuel level. They lowered the reference point.
 
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Re: Fuel system configuration/line size
Reply #18 - 05/19/12 at 17:21:26
 
I called Holley tech support today. The fella there said either I have a leak or the fuel is boiling. Since I only seem to have the problem after shutdown, fuel boiling would be the likely suspect. He said what I've done so far is pretty much what could be done to correct the issue. Since it hasn't helped, my choices are few. He said the secondary bowl is normally the first place for this to show up as fuel sits there not being used more than the primary, therefore has more time to preheat. He also said the ethanol blend fuel has a lower boiling point with winter blends showing signs of boiling at temps as low as 100 deg.
  I could modify the fuel system to recirculate off the fuel connector at the carb, using either a fuel log with a "pill" return or making up my own using a fitting like this: http://www.holley.com/17953NOS.asp . That would mean I would need to remove the fuel return from my RobbMc fuel pump. Or run an electric pump and use a return regulator. That would mean modifying the fuel tank for a sump pick up. Either way requires new plumbing for the return line. Not something I would look forward to as all my plumbing is currently stainless steel, and it's hard to run new lines neatly with the car assembled and no lift.  
  Otherwise, I'm not sure if switching to an Edelbrock carb would make a difference, or spend several thousand dollars to install EFI.
 
Dave Z
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Re: Fuel system configuration/line size
Reply #19 - 05/19/12 at 23:25:27
 
From the pictures it was hard to see the "window" was lower on yours than to old bowls, looked the same to me and why I said to lower it.
Now if I understand you you have a return setup now and if so how is it run?
With any pump you run why cant you run a return like AMC did with thier 3 fitting fuel filters? They were after the pump and before the carb. It had 1 inlet and 2 outlets, 1 of the outlets was small and had to be at the top. Dont see why you could not use a T and the pill to choke off the flow some. Just dont know if your tank is set up for a return or not?
Now if the fuel is boiling in the carb  how is this bypass going to work? I thought AMC added the return for vapor locks? Fuel boils in the supply line not the carb and with the fule always moving it would not sit and boil?
If me and I had a 2nd carb to throw on it for testing I would or even a plastic spacer for testing. Maybe 2 gaskets between manifold & metal spacer and 2 between metal spacer & carb. At this point I cant see the carb getting heat from the 4 studs & nuts can you?
Like you I am now all out of what if I try...........
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Re: Fuel system configuration/line size
Reply #20 - 05/20/12 at 00:21:03
 
Quote from FuzzFace2 on 05/19/12 at 23:25:27:
From the pictures it was hard to see the "window" was lower on yours than to old bowls, looked the same to me and why I said to lower it.
Now if I understand you you have a return setup now and if so how is it run?
With any pump you run why cant you run a return like AMC did with thier 3 fitting fuel filters? They were after the pump and before the carb. It had 1 inlet and 2 outlets, 1 of the outlets was small and had to be at the top. Dont see why you could not use a T and the pill to choke off the flow some. Just dont know if your tank is set up for a return or not?
Now if the fuel is boiling in the carb  how is this bypass going to work? I thought AMC added the return for vapor locks? Fuel boils in the supply line not the carb and with the fule always moving it would not sit and boil?
If me and I had a 2nd carb to throw on it for testing I would or even a plastic spacer for testing. Maybe 2 gaskets between manifold & metal spacer and 2 between metal spacer & carb. At this point I cant see the carb getting heat from the 4 studs & nuts can you?
Like you I am now all out of what if I try...........
Dave ----

Dave,
  Man, I told you there was a difference but you just didn't want to believe me.
 
  Return is off the RobbMc pump as stated earlier.
 
  Electric pump allows for a bypass regulator to be used and it could be placed closed to the carb, regulator cannot be used with a mechanical pump due to the pulsing. The three port filter is 5/16", the rest of my fuel supply system is 3/8". I didn't want to add a restriction and the adapter fittings.
 
  Fuel return from as close to the carb as possible would keep the fuel less prone to sitting and picking up heat and therefore dilivering the coolest possible fuel to the carb.
 
  Mechanical pump is bolted to a heat source, the block. Electric pump is not mounted to a heat souce.
 
  I currently have two gaskets between the manifold and spacer, spacer to spacer, and spacer to carb. Holley tech said the phenolic spacer I have should have been sufficient and adding more insulator wouldn't make a difference in his opinion.
 
  I thought about the studs and nuts as well, but putting my finger on them when I have the problem they really aren't that hot.
 
  At this point, my son wants to ditch the carb and go with EFI. That's his choice, I'll be keeping the carb for another engine though, I still need to find a solution at some point.
 
  Dave, thanks for putting in the effort and responding. I just find it hard to believe I'm the only one with this problem. Either anyone running a Holley on the street is using race gas, low boiling temp gas is only sold to me and my son, or there are not street driven cars with Holley carbs.
 
Dave Z
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Re: Fuel system configuration/line size
Reply #21 - 05/20/12 at 02:49:31
 
Quote:
Dave,
Man, I told you there was a difference but you just didn't want to believe me.

If it makes you feel better I dont listen or belelieve my wife at times too  Wink
1 more thought, I am guessing you are running Hi Test? If so would not hurt if you try a different brand of gas. I remember my parents had cars that would run like crap on 1 brand but run good on another. Run the tank down low then add or fill with the other brand gas.
Worth a shot till the EFI gets installed right?
If you have already done that then a carb swap till the EFI?
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Re: Fuel system configuration/line size
Reply #22 - 05/20/12 at 12:08:54
 
Finally a breakthrough. (or not) After pages of Google searches where people had the same problem that always gets blamed on the fuel bowl overfilling and never gets resolved, I found one case where someone suggested to check the air bleeds. If they are not open, fuel can syphon into the ventury. That seemed consistant with my problem. Keeping in mind the fuel may still aggravate things.  
See the picture below, the air bleed is not drilled completely. Only one side though.

The carb is probably out of warranty by now, should be interesting to see what Holley has to say.
 
Dave Z
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Re: Fuel system configuration/line size
Reply #23 - 05/20/12 at 14:26:40
 
Now why didnt we see that in the first picture of the carb you posted undecided
Think Brian had the same issues with his matty wonder if he runs the same carb or has the same issue with it not being drilled out?
Would be nice if drilling it out fixes it
Good luck
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Re: Fuel system configuration/line size
Reply #24 - 05/26/12 at 01:16:25
 
Problem solved. I contacted Holley, they said send the defective carb back. When they recieved it, they sent a new one out. Carb is on the car and problem looks to be corrected. After it gets driven some, I'll start undoing my other fixes. The altered fuel line and the phenolic spacer.
 
Dave Z
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Re: Fuel system configuration/line size
Reply #25 - 05/26/12 at 13:44:01
 
Good to hear they took care of it. Guess they had some go out that failed QA?
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