Fuel Line Nuts - In & Out (2025)

You want to support the throttle body with a wrench when you put those
fittings in, OR take them out. I broke one years ago taking it out.

I found a supplier who manufactures those fittings. They are expensive
because of low volume production. I may have saved it, but the easiest
solution is the junk yard.
I can not find the article I just read 2 days ago which said Manny, Gene
and someone else sourced the SS braided lines for the GM TBI. One is
long enough to reach to the filler neck.
Perhaps someone knows where to find the article or has purchased the lines?

Here's the info on what I used to go to AN fittings:
Russell 640800 GM TBI Adapter Fitting -06 to 12mm x 1.25 O-Ring Seal
Bought from an eBay seller for

Ken,
When I had my tanks down, I had a fitting welded to the top of the front tank so I could have the return from my mechanical fuel pump routed to the front tank. When I eventually go to EFI, I will use this fitting for the return from the pressure regulator. I mentioned this plan to our good friend Bob Drews and he expressed a concern about aerating the fuel with this arrangement. He suggested bringing in the fuel at the bottom of the tank or installing a dip tube from the top. Does this sending unit provide that arrangement?? As a matter of information, I did find that the rear tank had a pickup tube inside the tank for the Onan but it was sealed on top because Coachman did not use this location for the Onan ( my coach is a Royale). I think this was a mistake on their part. I drilled and tapped the bung that was at the top of the tube and ran a new fuel line to the Onan. I am a strong believer that if the Onan drains the rear tank ,one knows that you have a reserve in the front tank. I also have heard about folks with the Coachman arrangement having engine fuel problems. The Onan float can be open because of Onan non use which would allow air getting into the fuel line to the engine. Same thinking that a return from the engine fuel system should only go to the front reserve tank to maintain a reserve. ie no question where the reserve is.
John B

John,
I can't remember having to cut off the return tube inside the tank sender I
installed, so I suspect it doesn't reach to the bottom of the tank -- and
the photos on eBay seem to confirm that. However, my memory and those
photos do seem to indicate that there is enough tube on the inside to allow
for easy connection of an extension with a compression coupling -- just as
I used to re-connect the pickup tube I had to shorten. I haven't lost any
sleep over the return-to-drain arrangement, so using the top entry is more
a whim than anything else. However, whatever the arrangement on the sender
is, it should be satisfactory, since it's what GM designed for the air
conditioned cars for which it was intended. The returning fuel had to fall
a lot further in them than in our pancake tanks.
My Birchaven also had an unused fuel pickup which is now used by the
Troy-Bilt generator. I too have heard of Coachmen engines being starved by
the Onan, so I was anxious to make that change.
Ken H.

Why would it matter if the Onan float was open? There is an electric solenoid valve on the fuel line. Did Coachman do away with this valve or put the T on the wrong side of this valve?

How can an open float on the Onan let air back past the solenoid valve?

On Coachmen-fitted GMC's, the Onan supply line is Tee'd into the engine
supply line from the rear tank. So if the Onan's float bowl is empty,
opening the needle valve, the engine fuel pump sees an air leaking supply
line and can't suck fuel. Selecting the forward tank should correct the
problem.
Ken H.

I'm sorry, I guess I am mistaken? I have 4 Onans and each of them has a fuel shut off solenoid just before the fuel pump. When the Onan is off, the solenoid is shut off, fuel can not get to the carb and air can not get back in the fuel line from the carb. Are all of my Onans unique?

Each of my 4 onans has a solenoid right before the electric fuel pump. When the oOnan is off, air can not get back from the carb. Are all of myOnans unique? These solenoids do not open unless the Onan is running.

On my 4 Onans there is a fuel solenoid just before the electric pump. It is closed when the Onan is not running. How can air get from the carb past this valve? Do I have 4 unique Onans?

No, you do not, that was added to later units because the tank pressure
on some coaches (not necessarily GMC and I don't know which) could over
pressure the fuel pump and float.
The older of the BF (4kW) that I have does not have the stop solenoid valve.
Matt Colie

I have 2 BF, one NH, and an Emerald Plus. I had assumed this fuel shut off was part of the low oil pressure safety circuit.