Carb Expert Advice on 74 FJ40

[VitaminC914]

I have a 74 and it has the original carb. Timing is set perfectly, truck idles nice but we were having an issue where it would die every time we come to a stop. My mechanic decided to block/shut off the return fuel line out of the carb by pinching the line with a pair of vicegrips. The return line goes into the frame on the passenger side. The truck came with an extra new Aisin Carb, and when we looked at it, it did not have a return line, so he decided to do the same for the Carb that is on the truck. So far it has not died and seems to be running much better.
Also and maybe unrelated, when looking at the firewall by the passenger side, there are 2 metal lines sticking out (See pics), does anyone know where they go?
Any help or diagrams are appreciated. We are not going to completely remove the return fuel line until we are 100% sure that it is the cause of the truck dying.

 

[pb4ugo]

I think the lines your pointing at are for the charcoal canister. Im pretty sure the 2 lines I circled are fuel supply and return.

 

[AntFarm]

Not a carb expert, but I have a US spec 9/74 build date, and there are at least three different OEM carburetors for that year. The US fed spec carb has a fuel return line but no EGR. US cali spec carb has fuel return line and an EGR (the cali spec carb is taller to account for the EGR spacer). The non-US carb has no EGR and no fuel return line. Years ago I swapped a freshly rebuilt non-US carb into my '74 and just plugged the fuel return line at the firewall and it ran great with no issues related to plugging the fuel return line. That particular era of non-US carb is one of the best IMO with the mechanical secondary and overall simplicity. Might be important to note that my Evap system is still intact and functioning. Hope that helps.

 

[Pighead]

until we are 100% sure that it is the cause of the truck dying.

Could be one or a combination of a few things I can think of right off (not a carb expert too, but I dabble).
1) that carb comes with a "Throttle Positioner" that's supposed to keep the engine from doing that. Could be it's out of adjustment or the diaphragm leaks or it's missing
B) could it be you're running the vacuum retard carb that came on that engine? maybe it retards too much as you come down to an idle? How can you tell if your timing is set perfectly?
III) maybe is your float level set too low and blocking off the return line somehow lets more gas into the bowl?
You can figure all this out by just fiddling with it. You don't need to take it to a mechanic ( is whoever left the vicegrips on the return line a real mechanic?), take more and better pics and we can help.
Might need just a simple tune-up.

 

[charliemeyer007]

Vice grips on rubber fuel lines - seems over kill to me.
9" stainless steel hemostats are $12 for a pair on Amoron. I use them for lots of different tasks.

https://www.amazon.com/Straight-Hemostat-Forceps-Locking-Stainless/dp/B07CRM7XB3?tag=ihco-20

Then there are the carbide jaw ones (needle drivers). I have sewn tires/shoes/and other heavy duty stuff with them 10" $19

https://www.amazon.com/Cynamed-Needle-Tungsten-Carbide-Inserts/dp/B07W8TTK6G?tag=ihco-20

 

[mattressking]

Put a vacuum gauge on it. Tell us what vacuum is at idle when running. Your truck operates on vacuum, so vacuum is always the first place to start then spark and fuel level in sight glass.

Dying when coming to a stop is a failure to maintain air/fuel balance so you either have too much fuel (likely not if you can easily restart) so you likely have a condition where you have excess 'air' (or too little fuel to match because guess what, you don't have MAF/MAP and O2 sensor to make those adjustments via ECU).

Pointed hardlines are your charcoal canister ports.

If changing carbs improved condition, then you found one fault area to inspect, but return line won't affect running condition as long as it is either capped off or routed to fuel pump.

 

[VitaminC914]

Thank you everyone for all the pointers.. just want to clarify that my mechanic who is amazing, put the vice grips on the fuel line as a temporary measure for me to test drive and see if it dies. If blocking the fuel line worked, we are just going to eliminate it and obviously remove the vice grips.

I will drive it a bit more in the next week or two.. still not great weather here in MI.

 

[65swb45]

Adding to the points made by @mattressking, AF mixture would be drastically affected if your brake booster was developing a leak. Further, this symptom is most likely to occur coming to a stop. This should be something that your mechanic can test for too.

FWIW, I routinely delete the fuel return line on the 73&74 carbs I rebuild here. No one has ever expressed an issue with how their truck runs without it.

Marks Off Road Home Page - https://marksoffroad.net/index2.html

 

[65swb45]

Update?

 

[VitaminC914]

Update?

I have not been back to the mechanic. I did drive it about 15 miles in one direction and it did not die. However, on the way home, it died at every light. When I got home, I heard a whistling sound and when I removed the fuel cap, there was a lot of pressurized fumes. I thought that maybe my cap is not correct, but I looked online and it looks OEM. Not sure what to think anymore. We are definitely going to disconnect the return fuel line and now I am wondering if the lack of a charcoal canister has anything do it with it.