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Discussion Starter #22
Just wondering how you made out with the new adapter and fuel line?
I didn't. The 3/8 NPT was too big for the carb. Than I called Summit and spoke with them. He was pretty stumped on what would fit. They sent me another one they thought would fit, 1/4 NPT, but the male end was way too small. Finally decided to put the old Holley 600 cfm carb back on and use a small piece of rubber fuel hose to the banjo fitting.

Car actually runs better with the 600 cfm carb than it did with the 500 cfm carb.
 

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It's not NPT. I believe what you need or want is IFM 1/2-20 to IFF 3/8-24 adapter. Anyway on the Summit supplied line, that end you want a IFM or Internal Flare Male.
That's on my to do list as well. I want to make a short, offset line with a bubble end to the fuel filter. I bent my own line from the pump to fuel filter

755798
 

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Question for all you machinists out there. 3/8 NPT to 5/16 adapter doesn't fit the fuel rail on the Summit carb. I got the one mentioned above and the fuel line from the pump is a 5/16 and fits but the male 3/8 fitting is too big for the fuel rail. See pics below.

Called Summit today and they were stumped. They said the fitting I got may be mislabeled. The adapter I got from Summit is tapered and the mid point reads about .67". They also said I may need a 1/4 NPT to attach to my fuel rail. Wouldn't this be too small? If I measure the supplied fitting from Summit that came with my carb it looks like it's .61" at its midpoint. Summit is sending me a 1/4 NPT to 5/16 inverse flared adapter at no cost. Just not sure it will fit.

I looked at some tables about NPT and I get that what the size says will need a bit larger to thread into. Wouldn't I need a 1/2 NPT to 5/16 adapter?

Is my adapter mislabeled? What do I need? Are we sure it NPT?

I'm confused!
Sounds like an adapter issue. 3/8NPT is 18 threads per inch with a starting pitch diameter of 0.61201" and midpoint diameter of 0.6375. It should be hand tight after engaging about 1/4" of threads with a maximum thread engagement of 0.4078".
 

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5/8-18 inverted flare makes perfect sense, as it's for a 3/8" steel line. You might be able to get a heavy line nut that'll fit 5/16 line, or use a reducer.

 

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Discussion Starter #27
I may look at it later. Right now the weather is nice, the top is down, and the car is running great with the Holley carb on. Gonna leave it and drive it for a while!
 
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