Fuel line into Rochester 4 bbl. carb leaking

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Hello Folks. I recently replaced fuel filter in Rochester 4 barrel carb; it's inside carb : long paper element. Vehicle is 1981 Pontaic Parissienne, 305 - V8 engine.
After first installation, there was noticeable dripping of fuel at the small, outboard nut; the one on fuel pipe.
- I removed fuel line + added teflon tape to threads of small nut; now there is a slight presence of gas detected
I used new plastic gasket on inner, large housing nut. I don,t think that is source of leak. It seems to be coming between fuel pipe outside diameter + small nut inside diameter. Presumably flare on end of metal fuel pipe is not mating correctly with outside of large nut. Any ideas re: solving leak? I've thought about reinstalling with " Seals-All " sealing compound on inner diameter of small nut ; or perhaps installing new fuel pipe from pump to carb. The present pipe has a "SET"; i.e. it is somewhat difficult to line it up with carb housing to reinstall. I don't know if this has anything to do with problem. No leaks before re + re for new filter. Please reply to NG. Thanks, -JS
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First make sure that the leak really isn't coming from the large gasketed housing nut. Sometimes the plastic gaskets slip out of place at the last minute when your tightening them and then don't seal.
If it really is coming from the small nut then you have to take it apart and look carefully at the flare and inside at the flare sealing surface. Make positively sure that you haven't cross-threaded the nut - if you do then it goes in crooked and the flare isn't pressed together properly resulting in no seal. Make absolutely sure the flare and seating surfaces are completely clean. Make sure the pipe with the flare on it is not cracked. Make sure when you are screwing the nut down that the pipe is not cocked to one side. And make sure to use flare wrenches not regular wrenches.
The times I've seen these leaking is when someone has cross-threaded the nut or when the flare on the pipe is cracked. If the nut was cross threaded and someone cranked down on it in an attempt to get a seal, then the threads are ruined, the flare nut is ruined, and the flare on the end of the pipe is probably ruined. You will have to replace all those parts (the fuel line, the housing nut in the carb) or what you can do is take the housing nut out, and use a 1/4 NPT tap and tap it for pipe thread, then using pipe joint compound, thread in a 1/4 nipple and make sure to clean out all shavings, then take the fuel line and cut it about 6 inches back from the flare, and then clamp on flexible fuel line.
Ted
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QuestionAuthority wrote:

You're not supposed to use teflon tape on the flare. It's not pipe thread. My advice - take it all apart, dry it up, reassemble it. The leak will probably go away.
My $0.02 -> Those filters inside the carb inlet are a PITA...
Ray
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<snip>

Oh pray tell.......school us on the art of not using teflon tape on this fitting. I've been doing it on every flared fitting from brakes to fuel and have NEVER..I repeat now...... NEVER had a leak when using it.
I am sure a handful of us would like an explanation of this wonderful revelation. I'm up to learn something new.
Eightupman
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and
Better yet, why don't you school us on the benefit of using thread tape on a tapered flare compression fitting. Go ahead, try.;)
H
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The Teflon tape compresses into any void:
That would exist on the inside ferrule of the double flare, or the fitting flare. Thus, stopping any chance of a leak if there were any irregularities in either the tubing or the fitting.
I hope this explanation suffices?
Refinish King

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irregularities
King A good flare joint will not leak. If it leaks, under reasonable compression, parts need to be replaced. Period. Gas lines on top of the engine and brake lines are not good places to throw band-aids. I can't believe you would advocate such a thing. H
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Hairy wrote:

What is really scary is that the low pressure from the fuel pump is causing it to leak! That has to be one f'ed up fitting! I'm trying not to picture the teflon tape on brake lines. "Oh the humanity!"
--
Tony

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I'm not advocating it:
I do it as a fail safe on any jointm flare, double flare and compression.
Overkill is better than hindsight.
I replace over 50 brake lines a year, never a leak or a loss.
Refinish King

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Refinish_King1 wrote:

Not always. For bolts that are torqued to x foot-pounds, do you add an extra 20% for safety? If you do, you probably have a large collection of stripped fasteners. Just because you think it's a good idea doesn't always mean it's right. :)
(that said, it seems you can get away with teflon tape on flare fittings, but my experience has been it's unneeded and often directly contradicts the instructions that came with the equipment.)
Ray
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Hairy wrote:

I got it! The slipery teflon allows the fitting to blow apart easier?
--
Tony

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and
Haven't you realized that the flare nut turns on the line? Thus there is a gap between the nut and the line? One that is not filled by teflon tape? Sealing does not take place in the threads of the flare nut.
If the flare isn't seated properly it will leak and no amount of teflon tape will prevent it from leaking. If the flare is seated properly and the fitting is tightened enough then it will not leak, whether you use teflon tape on the threads of the fitting or not.
I've never used teflon tape on flare nuts and I've never had a leak on one that wasn't crossthreaded and had an intact flare.
Ted
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Eightupman wrote:

Hey, I'm just going off the instructions for my nitrous kit, which explicitly warned about pipe sealant - where to use it and where NOT to use it. (and no teflon tape with nitrous because it'll probably plug the lines, use only pipe sealant.)
AN (37 degree) and conventional flare (45 degree) lines DO NOT use any sealant - the sealing is done within the actual joint. (the machined faces.)
Pipe Thread - thread sealant is used.
Never used any thread sealant with the AN fittings and 1000psi nitrous lines. Or brake lines. My brain fart came last summer when I was plumbing the fuel system on my race car - 2bbl dirt track Camaro - at 2am I was trying to thread pipethread fittings into a flare and even with teflon tape it would leak... (duh)
Do a google on "teflon tape flare" and see what if you can find a page telling you TO use it on a flare fitting.
Ray
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Right, I could see the nitrous have an adverse effect on the teflon.

Probably boogered up the flare fitting, as suggested by other posters. your, right though, no amount of tape will compensate for that.

http://www.perl.org/tpc/1998/Applied_Perl/Perl%20Hardware%20Store/Hardware.h tml#Teflon_Tape http://ths.gardenweb.com/forums/load/plumbing/msg0811414121921.html
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Eightupman wrote:

Just goes to show you there's no such thing as always or never for these rules. :)
Seriously, my experience and reading says:
Flared / precision - don't use any sealant. Unless it leaks. Brake lines, AN fittings, etc. Pipe threads - sealant needed. Especially cheap parts that seem to have the threads cut by a drunk with a hacksaw... but you can't replace... Too much sealant is also as bad as not enough - gets in the lines, etc.
One "old mechanics tale" is sewing thread or dental floss as sealant in brake lines that leak around the fitting. That one works...
For your carb - do they make a tap with the appropriate threads? If not, probably OS it and pipe thread it... then curse GM for those fuel filters...
Ray
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So....as I had asked I have LEARNED something new today, even through all the snide remarks and comments! Teflon tape acts as a lubricant, not a sealant. Cool. SO, every fittin that I have done has been well lubricated to the point of the flare making secure contact with the mating surface. While some may not use it, I will continue to do so because I have seen no detriment to this point.

and
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Eightupman wrote:

I think you can probably get away with using sealant on flare lines even if not needed, but it's unnecessary.
Is ok, we all learn new stuff - I finally was able to weld an exhaust together this year for my race car that actually doesn't leak and fall apart. (I still leave roll cage repair for real welders...)
Here's a question -> why are roll cages in race cars almost always round tubing? Wouldn't square tubing be easier to cut and join? Nice 45 or 90 degree joints... I have a few theories, but I dunno the reason other than "because it's always been done that way..."
Ray's theories on round tubing for roll cages vs square tubing: Cheaper? Easier to bend than square tubing. Easier on the head (helmet) if you contact it in an accident - no "pointy edges" Stronger per pound/volume than square tubing because there's no "sharp edge" for localized stress?
Like I said, only theories.
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<snip>

I am not a metal man, in any way shape or form. But am always willing to theorize as well. Could it be the sharp angles of the steel become a weaker point, vice the arc of the round tubing? I would have to say that if square tubing was the wave of the future (or more recent past) NASCAR would have incorperated it long ago. The top of the line chassis (computer technology/bluprinting) program that DEI started was all done in round tubing. If square was in, I think it would have been tested there and if sound......used in the cars.
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Look in the metal newsgroups:
They always discuss the diminsional integrity of tubing, and how a square tube is not as strong as an oblong tube, but a round tube in the comparable size of a square tube is stronger than the square tube.
Refinish King

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Ray wrote:

Round is stronger than square.
--
Tony

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