You always have one of the best educated answers in this forum. I greatly respect your insight and knowledge. However, in this instance, in 50 years I'd done custom bent & flared fuel lines, but never a double flare and never had a leak. Never.IMO.....the Holley carb, albeit a Model 4150 or 4160, uses s 37-1/2° male inverted flare nut connection for the fuel inlet fitting on the primary and secondary fuel bowls. The line size is 5/16" but the high air flow carbs may use a 3/8" fuel line and a correspondingly larger carb inlet fitting. The other major difference is the dimension of the inlet centerlines, with the Model 4150 being longer due to the differences to the secondary metering block vs secondary metering plate in the Model 4160. To insure a "no leak" installation, it is imperative to use s properly double flared connection fitting WITHOUT any pipe dope or teflon tape on the male inverted flare inlet connection.
W-ERobby,You always have one of the best educated answers in this forum. I greatly respect your insight and knowledge. However, in this instance, in 50 years I'd done custom bent & flared fuel lines, but never a double flare and never had a leak. Never.
Hey, I figured this was one of those instances where I'd pat myself on the back... or, more accurately, say how lucky I've been !!! Absolutely... "far less experience" ! It goes without saying, who's actually doing the work makes a difference. You hit the nail on the head: concentric . Slop mechanics are the ones that try to wrestle fittings in at 45 degree angles and expect no leaks ! LOL !W-ERobby,
Thank you for your kind words.....your success rate is to be commended. The only reason I suggested a double flare connection (for someone with far less experience experience), was to insure that there would be more material presented to seal against at the inverted flare connection. Most flared fitting leaks, IMO, are due to inaccuracies presented by the person performing the flaring, ie: flare not concentric to the tubing centerline or incorrect flare angle or excessive thinning of the flare angle leading to "pinch off" of the flare joint or cracking of the tube. Most carburetor fuel lines are low pressure applications, 10 psi or less. A single flare should be more than adequate, with copper tubing. However copper is subject to fatigue failure due to vibration, and is generally not recommended. Hydraulic brake lines (steel or "Bundy-flex tubing" an alloy) operate at higher pressures, which can exceed 1000 psi under panic braking conditions plus are susceptible to vibration extremes, where a double flare connection is ALWAYS mandatory. Just a few additional talking points......