Paul Ceresa

58 Chevy fuel problem

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Posted (edited)

,Getting air bubbles in fuel line not related to heat from exhaust. I think fuel is boiling due to low boiling point of rec 90 fuel. Rigged up temporary  fuel tank in front of front bumper to eliminate exhaust heat influence. Changed fuel pump, installed 6 blade fan, redid heads, intake manifold, carb, fuel lines and fuel tank and fuel cap (vented). Any ideas?

Edited by Paul Ceresa
forgot comma (see edit history)

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Try switching to a non-ethanol gas. I've had those problems before, & I'm pretty sure it's the ethanol. I went to non-ethanol & my troubles disappeared. 

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Check the rubber hoses on the suction side of the fuel line, including at the sending unit. A rubber hose can leak air in but not necessarily leak fuel when idle.

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Thank you for your insightful advice. I failed to mention that the 283 runs very well for about 40 minutes then bubbles from the discharge side of the mechanical fuel pump reach the carb and it starts to fall apart. I rigged up a dump valve between the fuel pump discharge and the carb with a 1/4 turn valve and when I bleed the line air comes through and then it runs smooth again. Operating temperature is around 185f as determined by a thermometer radiator cap. When you say the sending unit can you elaborate? I am a relative novice. Thank you. As a side note rec 90 MSDS sheet lists boiling point of 128 f on the low end.( Since gasoline is seasonally and regionally blended )Someone told me to mix one gallon of diesel fuel to eleven gallons of non alcohol fuel, which is what rec 90 is to raise the boiling point of the fuel.

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Yes, I am using a non ethanol fuel. It seemed to get worse when I quit using a lead additive and am wondering if I should return to it and at what ratio.

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Is the fuel tank the original one?

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3 hours ago, Paul Ceresa said:

Changed fuel pump, installed 6 blade fan, redid heads, intake manifold, carb, fuel lines and fuel tank and fuel cap (vented). Any ideas?

 

You did all this for bubbles in the fuel line?

 

By fuel lines, do you mean the rubber sections, or the steel sections also?

 

Fuel pump NOS or new production?

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Paul, welcome.

  You must do what Bernie [ 60 Flat Top] said.  Appears you may be  sucking air. Sending unit mentioned is mounted on top of the gas tank and incorporates the suction line from the tank.  This the sending unit for the gas gauge. There may be a rubber hose where the gas line connects if the unit has ever been replaced. Also a rubber hose/line between the suction of the fuel pump and where the gas line comes from the frame.

 

  Good luck

  Ben

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Had the same problem on a 67 275hp 327. Steel fuel line was too close to the block on a Camaro with AC. Wound up making a much longer line and problem was eliminated. Haven't had that issue since I've been running the engines cooler. On a 58 I'd use a 160 thermostat.

 

Is this in a boat ?

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Yeah, had rust in the fuel tank so I replaced it and installed a new pick up tube/filter and fuel sending unit. Replaced fuel lines with 3/8 rubber and have 3/8 metal ready to install once I can get it on a rack. It is sort of a Frankenstein engine. Block, heads and intake manifold didn't all match for exact year. Originally I thought I had a carb problem so I put on a Holly and adapter plate. After that I found a problem with the intake manifold so replaced that when I sent out the heads to be redone.  I will reroute the fuel line away from the exhaust manifold further.160 thermostat too. Both  good suggestions. The fuel pump is a heavy duty American made mechanical. First replacement was cheap and I didn't trust it. Like I said runs great for the first 40 minutes or so then the bubbles appear. Did a vacuum test on line when cold and didn't find anything. Haven't done the test when hot yet. I Thank each of you for your input.

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Just one other thought: in the 60s SBC (small block chevvies) had two different fuel pumps. Non-ac cars did not have a return line. Cars with AC did. Was said to reduce vapor lock.

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Posted (edited)
2 hours ago, padgett said:

Just one other thought: in the 60s SBC (small block chevvies) had two different fuel pumps. Non-ac cars did not have a return line. Cars with AC did. Was said to reduce vapor lock.

 

Not in 1958, or through the mid 60's for that matter. In 64 the 409 cars were the first passenger Chevy"s with a return line.

Edited by John348 (see edit history)

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5 hours ago, Paul Ceresa said:

Yeah, had rust in the fuel tank so I replaced it and installed a new pick up tube/filter and fuel sending unit. Replaced fuel lines with 3/8 rubber and have 3/8 metal ready to install once I can get it on a rack. It is sort of a Frankenstein engine. Block, heads and intake manifold didn't all match for exact year. Originally I thought I had a carb problem so I put on a Holly and adapter plate. After that I found a problem with the intake manifold so replaced that when I sent out the heads to be redone.  I will reroute the fuel line away from the exhaust manifold further.160 thermostat too. Both  good suggestions. The fuel pump is a heavy duty American made mechanical. First replacement was cheap and I didn't trust it. Like I said runs great for the first 40 minutes or so then the bubbles appear. Did a vacuum test on line when cold and didn't find anything. Haven't done the test when hot yet. I Thank each of you for your input.

 

So you are running rubber hose from the tank straight through, no steel lines?

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Interesting about the 40 minute time lapse. Have you gone to the back of the car and loosened the gas cap when it does that?

 

Today's fuel hose in labeled in inches but manufactured in millimeters. If you try using the original Corbin clamps you will find they are too large to compress the outside diameter of the hose. When users discover this they will change to a worm gear clamp. Even though you can get a 3/8" worm gear clamp they do not have the full circumferential clamping pressure of a Corbin clamp. They can be over tightened and oval the fuel hose and possibly make an air leak. It is a remote possibility that happened but worth checking.

 

If it was mine I would cap the fuel line at the sending unit and use a MyTeeVac at the carb inlet to rule out an air leak first.
 

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On 10/4/2019 at 12:53 AM, John348 said:

 

Not in 1958, or through the mid 60's for that matter. In 64 the 409 cars were the first passenger Chevy"s with a return line.

1963 was 1st year for the 340-400-425 hp.

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