Fuel line into Rochester 4 bbl. carb leaking

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

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

I'm not sure by your wording, but the nut and the outside of the flare are NOT where the seal should be. The seal is made between the inside of the flare and the mating surface of the fitting on the carb. The nut only holds the two pieces together.

The nut doesn't make the seal, although by adding the teflon tape, you are attempting to make the nut make the seal. Take it apart and check the proper mating surfaces for defects. And as mentioned in another post, did you use a wrench desinged for flared pipes? If not, the nut can easily become deformed and not be able to do it's job.

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

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

I always thought the teflon tape was just 'anti-seize' on the flare nut. Am I missing something??

Regards, Al.

Yes....No mechanic that's worth a damn would ever put thread tape on a flare nut. If you think you need anti-seize on the threads, then just use anti-seize.

H

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

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

humph...I must not be worth a damn...but yet get return customers, ,and referrals. Ah well, I guess a blind squirrel gets a nut every now and again...

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.

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.

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.

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.

Just goes to show you there's no such th 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

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

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.

Ref>> So....as I had asked I have LEARNED something new today, even through all

Yes!

Us blind squirrels get some nuts as opposed to opionated do it your selfers at times. I dont use the tape on the nut, I use it on the flare it self!

Refinish King

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