Hey guys:

I'm dealing with the installation of fuel lines on my project vehicle. Since the intake has been changed, the relationship(distance) between the fuel pump and carb has changed as well. As a result I am making up some custom lines.

In the course of deciding which route to go, I bought some fittings that were intended to attach to the line fitting on the carb and the same at the fuel pump.

Evidently I don't understand enough about metal fittings. I bought a 3/8 NPT fitting which will not screw in the carb past maybe 1/8 turn. The old line and fitting, which to the naked eye looks exactly the same, screws in all the way with no problem. I tried two different kinds of 3/8 NPT fittings to make sure I did not simply have a defective piece and neither will work.

So, what am I missing here? Do the NPT fittings I purchased lack the proper taper? I'm looking forward to working up some metal fuel lines soon but I will be throwing money away if I again purchase something that will not screw into the carb and fuel pump.

This by the way is a standard GM fuel pump on one end and a Quadrajet on the other with 3/8 line between them.

Any advice much appreciated

 

I don't think the fitting has a taper. Its intended to tighten the flared end against the fitting in the carb. Do you have something like a NAPA auto parts store nearby? Some place that has bins full of fittings you could test thread into the carb or your old fuel line to identify what size/thread type you need? Sorry, I don't know the name of the thread you need. But what your describing doesn't sound like the right one.


John

 

No 3/8 npt will not work they are tapered pipe fitting.The fittings you need are straight pitched used with 3/8 tube.I bend and flare my own lines when needed.

 

Correct.

The fuel lines use inverted flare fittings, the same as brake lines. You need a double flaring tool to properly flare the hard line. Sorry to be blunt, but didn't you look at the old fuel line when you took it off? Those old fittings sure don't look like NPT fittings...



Note that inverted flare seals on the flared part of the tube, NOT the straight threads. An NPT fitting forces the tapered threads together for the seal.

 

Damn, Joe P.
You nailed it again
where did you get that synopsis of the inverted flare fitting?

 

I think he has a library of all this stuff, breaks it out once in a while to keep us humble.......

 

Google Images is your friend.

 

Power is Knowledge.

 

makes sense I can feel myself getting smarter as my 455 gets closer to replacing the 350 in my car now !!!

 

I think you have that backwards.

 

The subtle point I was trying to make is that, while we usually live by:
Knowledge is Power
if you find you don't have the knowledge, then
the Power of google is Knowledge.

OK, I'll crawl back in my hole now.

 

Tyler, were you able to find what you needed?


John

 

Nice save!