Best fuel line thread sealant?
 

I looked but could not find a thread on this topic. I replaced the old dilapidaded metal fuel supply line that runs into the filter of my GMC's Rochester 2 barrel carb with rubber fuel hose and used brass fittings to attach the ends to the fuel pump, and the carb. The brass fitting at the carb (fuel filter area) leaked even though I used some NAPA thread sealant on it. So I removed the fitting, put a larger amount on the threads, reattached it, and fired up the engine. At first it did not leak at all, but then a very slow drip began. I checked it, and it appears that the gas is turning the thread sealant to liquid. What should I be using instead for sealing this brass fitting thread? Silicone perhaps?

Re: Best fuel line thread sealant?
 

Might need to post a picture of carb and fuel line area's where they meet. Sealer is almost never needed, unless something if fouled up. I've never seen any brand of vehicle where sealer was needed, or could even be used.
I'm trying not to sound like a Beavis, just helpful
Most carb inlets have a sealing washer of some type.

If it's the Rochester 2 Bbl, like I've seean a few, 1st there's a fitting/nut that screws in to the carb, AND a 2nd fitting the screws into that. Fuel line attaches to second fitting.

If the leak is coming from between the 2 fittings, teflon tape is the only recommended wat to seal that, because it is likely a pipe thread connection...

Re: Best fuel line thread sealant?
 

Teflon tape or pipe dope

Re: Best fuel line thread sealant?
 

It doesn't seal on the threads. It should seal on the flare. I wouldn't trust it, I would replace it for safety reasons. Also, never Teflon tape fuel lines because small pieces can get into fuel system and clog small orifices

Re: Best fuel line thread sealant?
 

Here is the carb and fitting. You can see the white melted thread sealer on the intake.


https://imagizer.imageshack.com/v2/7...923/Etyu6w.jpg

Re: Best fuel line thread sealant?
 

Wrong type of brass fitting.

With the rubber hose attached I would suggest running a new metal line with proper flared ends

Re: Best fuel line thread sealant?
 

The new fitting you installed may not be the correct type for the fitting in the carb.

It may be that you have a pipe thread fitting screwed into the carb fitting, and you possibly need an inverted flare fitting. Inverted flare fittings are made, and look similar to your current fitting.

The fitting you need has an inverted flare on one end and a hose barb on the other end (like the one you have...) The inside of the fitting you need will look just like the inside of the steel tube and flare nut that you took off...

Maybe....

Re: Best fuel line thread sealant?
 

Thanks for the help gentlemen! I may cut the carb-end of the original metal line and use the metal end and fitting with my rubber hose.
I was unable to use the original line anyway since the new fuel pump had a different size fitting that would not attach to it.

Re: Best fuel line thread sealant?
 

Finding the fitting you need may be a challenge. You may need to go to an old timey parts store. Take the fitting that screws into the carb with you, and obviously you will need to know what that size of rubber hose was.

Sometimes the fitting you ned may be a 2 piece deal, similar to what the end of the cut off steel line would look like. but with the hose end have barbs on it to grab the hosee, so it will not slip off, AND seal better...

Using part of the old fuel line can be risky. Without the barb on the end, the fuel hose can slip off...I have performed the repair as you mentioned as a temporary fix...

Re: Best fuel line thread sealant?
 

My truck ran like this for years ("repair" before got the truck).
Slip the rubber line on far enough that you can put two opposed fuel clamps on it.

I would suggest making or having a metal line made if you're still using a block mounted fuel pump.

Re: Best fuel line thread sealant?
 

If you think the hose will slide off just put a single flare on the tubing.
You can make one with a small screwdriver stuck in the end and wound in a circle. That will create a small lip that the hose will slide over and grip.
Not a perfect flare but it works.

Re: Best fuel line thread sealant?
 

You need an inverted flare barbed fitting like this one....not a tapered pipe thread style fitting you are trying to seal....

Check your local auto parts store...

https://www.wildhorses4x4.com/produc...yABEgLMdPD_BwE

Re: Best fuel line thread sealant?
 

Here is what I was using. It looks uncannily similar to what is pictured in that link.
I ended up doing what I said with cutting the old metal line end and splicing it with the rubber hose (temporarily).

https://imagizer.imageshack.com/v2/7...923/F8u9Ic.jpg
https://imagizer.imageshack.com/v2/7...923/JSi9dw.jpg

Re: Best fuel line thread sealant?
 

I'm a fan of getting a steel brake line with inverted flare fittings at the car parts store, borrowing the pipe bender tool and flare tool that they loan out for free, and make a new all metal line. I am also a fan of these copper flare gaskets, because they make the flare fitting seal very well without having to torque very hard on the fitting.
http://67-72chevytrucks.com/vboard/a...1&d=1524530824
More of my ramblings about the darned fuel line and fittings:
http://67-72chevytrucks.com/vboard/s...62#post8242862

Re: Best fuel line thread sealant?
 

I've never seen copper gaskets for inverted flare, I'll have to remember these for leak prone stuff.

Re: Best fuel line thread sealant?
 

Well, crap, that fitting should have worked.....

That fittting might be able to be made to work....possibly the edge of the taper is stopping the tapered part from seating against the carb inlet nut.

I will try to find another type of that fitting, and take a picture of it, post it here...

Do you remember what size hose you used???

Re: Best fuel line thread sealant?
 

I used 5/16 fuel line.

Re: Best fuel line thread sealant?
 

It may not be called for in normal circumstances, but using teflon tape can be done safely without fear of pieces getting into the carb. First of all, you start winding it around the threads at the carb end so it is only on threads, not in the seat area. You wind it in same direction as threads and nothing could possibly get inside the tube or carb inlet.

Re: Best fuel line thread sealant?
 

That fitting is not long enough in the threaded section to enable the flare seat to contact the taper inside the carb fitting.

There are longer thread length fittings available in most auto parts stores....

I have used teflon tape on the threaded sections only in the past....but you would be better off with a longer thread section fitting.

You could also look for a fitting that has a flat seal area and a copper washer to seal against the flat section of the carb inlet fitting.

:chevy::chevy::chevy:

Re: Best fuel line thread sealant?
 

The flared part of the fitting not fully contacting evenly and sealing against the flared inlet because of imperfect surfaces or because of slight lack of depth is also possible to cure with one of those copper flare gaskets from Grainger. I'm the biggest fan of those little things.

Re: Best fuel line thread sealant?
 

I thought it looked like not enough thread depth to seat as well.

Re: Best fuel line thread sealant?
 

I'm not aware of a conical washer that is made for inverted flare fittings. The only ones I've ever used were for spacecraft fuel systems, where single flares were used. That use comes from aircraft use. I think that they (single Vs double flares) have a different flare angle, but I'm willing to be educated about that. The thing with copper is that it is malleable enough that it would conform to the slightly different flare angle. I would like to point out that if you use a copper conical washer, it is one-use only. Don't try and save money, for what they cost. Of course, at 7 PSI they'll probably seal again, But a spacecraft fuel system typically runs about 600 PSI. Aircraft hydraulic systems run much higher, and those washers just get tossed after removal.

Re: Best fuel line thread sealant?
 

It seems you have answered your own inquiry, grasshopper. You might want to rethink some of that, however. A single clamp can be used on the suction side of the pump lines. But anywhere the fuel is under pressure, it can find a way through a bad barrier. Your feed line into the carb needs to have a barbed end to secure a clamp which might allow a hose to pressure off a line otherwise, and in your case, creating a fire hazard under the hood while you tool down the road, oblivious to an underhood fire which could happen as a result.

Re: Best fuel line thread sealant?
 

I've clamped neoprene on straight cut fuel line with no leaking or blowing off issues. I'd be more concerned about the tube cutting the hose if not straight in line off of the union. As mentioned above, we are only talking approx 7#.

Re: Best fuel line thread sealant?
 

Teflon tape is NOT a sealer. It's purpose is to lubricate the threads in order to torque to proper specs without galling and to achieve a mechanical seal with the threads.