1978 FJ40 2F Carburetor return line flow questions. (1 Viewer)

[Helimancan]

The main question that I have is this... Did the original return line fitting on the carburetor or return line connection to the fuel tank have a restricted orifice or step down in size ?

I have rebuilt my carburetor everything works very well aside from the return line flow which affects my fuel float bowl level.

I have routed a hose from the return line fitting on the carburetor and i have tee'd it back into the fuel feed line upstream of the mechanical fuel pump.

At low RPM's everything functions well.

At higher RPM's the fuel float bowl level in the carburetor drops to a point where the engine starves for fuel.

I have solved this issue temporarily by pinching off the return line fuel hose slightly with vise grips to maintain my fuel float bowl level in the carburetor. It works but not ideal.

The main question that I have is this... Did the original return line fitting on the carburetor or return line connection to the fuel tank have a restricted orifice or step down in size ?

 

[Solace in Solitude]

I don’t believe so... I honestly never noticed. But, nothing ever jumped out at me.

My return runs from the carb return outlet, to the tank return inlet.

It’s possible, by tee’ing into the fuel feed line, you are causing the fuel pump to suck returned fuel (and not enough of it, when the secondary kicks in) and are thereby losing prime from the tank.

The secondary gulps a lot more gas.

Is this always occurring at higher rpms, or only when under load... e.g. petal to the metal, uphill?

 

[Helimancan]

Is this always occurring at higher rpms, or only when under load... e.g. petal to the metal, uphill?
[/QUOTE]

Hi Solace thanks for the reply.

The float level drops without load as well actually just holding the throttle open by hand in neutral I have watched the level drop.

 

[Solace in Solitude]

Why not return to the tank return port?

I think your return is causing your problem.

But, I was wrong yesterday too.

 

[Helimancan]

I only have an aluminum fuel cell in the rear which doesn't have a return line fitting. So unless I have the tank doctored up to accept a return line I may just have to cap the return line fitting.

 

[Helimancan]

The original mid body tank started to leak and I haven't been able to find a replacement I am almost certain that they are not available !

 

[Solace in Solitude]

Cap the return and drill a 1/8” hole in a cheap gas cap. See if that helps.

 

[Helimancan]

Thank you for all the advice !

My Aluminum Cell is vented very well through the vented cap when it hasn't fallen off or I haven't forgotten to put it back on

 

[SteveH]

I installed a 1982 2F in an FJ45 and had various fuel flow problems and ended up capping off the return line permanently, and the truck ran great. So, if capping off your return line doesn't result in float height issues, you may get what you need out of doing so.

 

[65swb45]

1. Cap the return line as suggested by others.

2. That may not be your only problem. You may have a fuel delivery issue as well.

 

[Helimancan]

1. Cap the return line as suggested by others.

2. That may not be your only problem. You may have a fuel delivery issue as well.

I will cap the return line until I can install a mid tank with a proper return fitting.

I have successfully pinched off return fuel flow to maintain float bowl level so I am fairly certain that it is a return flow issue now as well.

With regards to the fuel feed. I have also installed a new Aisin OEM style mechanical pump and it seems to be pumping as it should when the return is pinched back. My tank is clean pickup is clean fuel line is all new and clean up to the pump.

I was looking at the cutaway view of the 72-78 style FJ40 tank on Coolcruisers. The return on this tank is about half way up the tank so would normally be under fuel when your tank level is above half; it is also quite a bit smaller in diameter compared to the return hose that I have currently installed.

Now correct me if I am wrong. I am guessing that these are non vented pressurized tanks (72-78) looking at the vent/charcoal can system so this might also add a slight amount of back pressure to the return fuel flow along with the fact the the return is under liquid level above half tank ?

 

[Helimancan]

I installed a 1982 2F in an FJ45 and had various fuel flow problems and ended up capping off the return line permanently, and the truck ran great. So, if capping off your return line doesn't result in float height issues, you may get what you need out of doing so.

Steve do you happen to know what the diameter and pitch of the fitting might be for the carburetor return line fitting ?

 

[SteveH]

Not offhand. I initially clamped off the hose with a vise-grip pliers, and I don't recall what my long term solution was. Of course, you would want a robust, non-rubber-cap solution that would be fire safe. I would study the fittings and/or find a carb-guru with the correct knowledge of the fitting size and style. Maybe use an old section of fuel line with the end brazed shut?

 

[Helimancan]

Not offhand. I initially clamped off the hose with a vise-grip pliers, and I don't recall what my long term solution was. Of course, you would want a robust, non-rubber-cap solution that would be fire safe. I would study the fittings and/or find a carb-guru with the correct knowledge of the fitting size and style. Maybe use an old section of fuel line with the end brazed shut?

I had posted a new thread asking what the plug diameter and pitch would be.

Discovered that my fuel feed is connected to the banjo style fitting and this is what people are referring to as the return fitting.

My return hose has been connected to the other union style fitting which is facing forward. This being what others have been referring to as the normal fuel feed connection.

If this is right it means my lines have been swapped. It has been like this as long as I have owned the Toyota.

Right or wrong I do believe that the banjo bolt will give me the return restriction I need.

Worth a try !

 

[thebigredrocker]

Sounds like you are making progress. You can get a fuel cap that will breathe both ways, should you ever one, ping me and I can find the part #'s.

Banjo fitting = 13mm
Banjo Bolt = 11mm

On the 1976 carb pictured, the banjo bolt is a bastard 11mm coarse thread. The plug that goes in that hole is found on the top of 1970-1972 F carbs.

The banjo fitting & line nut has a bastard 13mm thread.

So Mark, What years had return ports on the carb.

I think February 1973 rigs came with a return Banjo on the carb

 

[lcwizard]

Sounds like you are making progress. You can get a fuel cap that will breathe both ways, should you ever one, ping me and I can find the part #'s.

Banjo fitting = 13mm
Banjo Bolt = 11mm




I think February 1973 rigs came with a return Banjo on the carb
View attachment 2072700

I must have an odd one. The carb I have appears to be a '78. the banjo bolt is 12mm 1.25pitch

 

[w460traitor]

That's what mine is too. '78 carb, M12 x 1.25.

 

[Helimancan]

Thanks everybody for the input !

My power train/drive line is also a 1978 year range.

Hopefully when I get back to the Toy here in a couple weeks I can report back with a follow up on whether or not I have solved the issue with all of this new information I have to use !

 

[65swb45]

I had posted a new thread asking what the plug diameter and pitch would be.

Discovered that my fuel feed is connected to the banjo style fitting and this is what people are referring to as the return fitting.

My return hose has been connected to the other union style fitting which is facing forward. This being what others have been referring to as the normal fuel feed connection.

If this is right it means my lines have been swapped. It has been like this as long as I have owned the Toyota.

Right or wrong I do believe that the banjo bolt will give me the return restriction I need.

Worth a try !

The picture @thebigredrocker posted for the VERTICAL banjo bolt is the 73-74 type, which DOES have a restrictor. The 75-78 HORIZONTAL banjo bolt does not have a restrictor.

SOOOOOO, if you want to try adding a restrictor into your return line, then you would need the earlier style bolt. Problem is, I've never tried to see if that bolt would fit in a 2F carb. It seems like a bandaid, and I don't advocate bandaids.

Fuel, like water, will take the path of least resistance. Logic says that if the hole in the needle and seat were insufficient, marginally increasing the size of that fitting would make it easier for the fuel to go INTO the carburetor than the return line, without the need to put a restriction in the return line.

That said, considering hundreds of thousands of engines and carburetors are out there running around without this modification, it is far more likely that the fuel delivery is inadequate, rather than the size of the opening in the seat.

I did open up a needle/seat assembly once, AFTER determining that fuel delivery was adequate. And it did solve the problem on that vehicle.

Cheers.

 

[w460traitor]

So given that the carburetor is a 78, it’s theoretically possible to just hook up an M12 connection to the carb using a copper O-ring (headed to the fuel tank) and call it a day? That is, without any restrictor?

My particular carburetor is missing all of this stuff, so I can't examine. I wasn’t sure if the bolt going through the banjo was a particular length, or a particular flare at the end that served to restrict fuel flow.

Sorry if I’m hijacking – I assumed I wasn’t because we appear to have a similar issue.