Paul Ceresa

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.

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.

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.

,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?