on a fuel line leading into the carbs there is a brass fitting..it screws into another brass fitting on the carb..in order to remove the fuel filters inside these carbs I have to get these two fittings apart..they are locked up like nobodys business..you cant remove the entire fitting as it twists the metal fuel line...I have to get them apart..period!... Cannot heat them as it IS a fuel line..this is on twin big block motors for a boat if ive confused anyone...any suggestions to get a couple brass fittings apart would be greatly appreciated..

can you heat up the thread junction with something other than a flame (shop light maybe) & melt some candle wax into the threads or the old standby WD40 applied daily for several days in a row

its soaking in WD now..

Tri-flow works better and faster than wd40 for this sort of thing.

You could unbolt the carb and turn it, instead of the fitting...

Are you using Line Wrenches?

One "trick", sometimes it actually helps to tighten the fittings (which can sometimes break them loose, especially if the fittings are damaged or rounded off a bit), before attempting to loosen/remove the fitting.

Another possibility, you could undue the fuel-line at the fuel pump, and then use two box-end wrenches on the fittings to try to get them apart.

If that doesn't work, hack-saw through the fuel Line, then remove the carb or just the float bowl, then you can work on it at a work-bench with Boxed-End Wrenches, Also, that way you can remove the fuel from the equation and heat the fittings a bit if necessary. I have had to go that route before.

You can also try some PB Blaster. Or, you can soak the fuel bowl with brass fittings, overnight, submerged in penetrant.

I had a similar problem with some transmission lines years ago. My father inlaw stopped by after I struggled trying to break them loose after a 1/2 hour of messing with it. He put two line wrenches on it. Then he held one tight and smacked the other wrench with a hammer. It broke loose instantly. Also IMO PB blaster works better then WD40.

As silly as it seems, get the handles of both wrenches within 20 degrees of one another and wrap both hands around the both wrenches. Squeeze them together to break it loose. It sometimes works for me when I'm dealing with something stuck hard.

As stated earlier, if you can't get box end wrenches on there then use line wrenches.
Open end stuff is not your friend in this situation.

Jim...

Line wrenches and a good penetrant...

WD is 'water displacement'...