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
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
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
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,
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
thread in a 1/4 nipple and make sure to clean out all shavings, then take
fuel line and cut it about 6 inches back from the flare, and then clamp on
flexible fuel line.
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...
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.
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?
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.
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.
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.)
Haven't you realized that the flare nut turns on the line? Thus there is a
between the nut and the line? One that is not filled by teflon tape?
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
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.
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
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.
Just goes to show you there's no such thing as always or never for these
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...
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:
Easier to bend than square tubing.
Easier on the head (helmet) if you contact it in an accident - no
Stronger per pound/volume than square tubing because there's no "sharp
edge" for localized stress?
Like I said, only theories.
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.
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.
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