‘77 fj40 cranks and runs for short period but then stalls

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I’ve come along way on this vehicle. Just two weeks ago it would not crank and I had no spark. I was able to find a short in the wiring harness which was causing me to not have power to the ignition coil. now it will start and run. I have also installed a new perTronics ignition system in the distributor cap. Now I am back to the original problem which is that the vehicle cranks and runs for a short period of time but then starts to sputter and stall. It feels electrical to me but could be gas related. What are the most common problems for a situation such as this? It will idle endlessly in the driveway, and when it stalls, it immediately cranks and idles again. Thanks in advance!
 
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could be a blocked main jet. The aisin carbs will still idle when the main jet is blocked.
remove The lug just below and to the left of the sight glass and poke a air nozzle in there and blow it out. Or you can use a guitar g-string to clean it out.
Good luck.
 
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A little more detail - it will rev up in the driveway. It seems to be taking gas fine until I drive it down the road. When driving around the neighborhood, after I get up to speed, it chugs and stalls. When it stalls, I can pop the hood quickly and look at the glass on the carburetor and it is empty. I can then pump the accelerator and re-crank it quickly and the glass is now full. I assume this means I have some type of fuel delivery problem. The previous owner replaced the fuel pump, and it looks like I have a new fuel pump on the vehicle. I hate to replace the fuel pump if that is not the problem. Any thoughts on what it could be other than fuel pump? Anyway to test a fuel pump other than replacing it?
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You need to install an inline fuel pressure gauge and monitor the fuel pressure under load (higher demand). The fuel pump was replaced for a reason, maybe it did not fix the issue. You could have sticky float issues as well.
 
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Make sure fuel is flowing freely from your gas tank. Might be some kind of junk in the tank or the lines. Rust in tank, rusty lines, some bad gas.

It sounds like the fuel is flowing, but too slowly to keep up with the engine demand off idle.
 
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OK, I think I may have found the problem. This is a picture of the way my fuel tank is attached. It’s hard to see from the picture but there is a hose that attaches to a nipple at the bottom right of the fuel tank. This is the hose that leads to the fuel filter which in turn leads to the fuel pump. When I detach this hose very little fuel trickles out. I assume
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the other hose was for the return. However, the PO may have gotten them reversed. Or these may be the wrong hoses/attachment points altogether. Can anyone please give me some insight as to how the hoses should be properly attached to the fuel tank. Thanks!
 
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OK, I think I may have found the problem. This is a picture of the way my fuel tank is attached. It’s hard to see from the picture but there is a hose that attaches to a nipple at the bottom right of the fuel tank. This is the hose that leads to the fuel filter which in turn leads to the fuel pump. When I detach this hose very little fuel trickles out. I assume View attachment 2765654the other hose was for the return. However, the PO may have gotten them reversed. Or these may be the wrong hoses/attachment points altogether. Can anyone please give me some insight as to how the hoses should be properly attached to the fuel tank. Thanks!
1629580324015.jpeg
 
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so i didnt get much feed back on the above post, but i think i was able to figure out online that the attachments are correct. however, the engine is still starving for fuel. i think the tank may have a blockage. what's the best way to clean out the tank short of ripping it out and putting a new one in?

Also, in order to test my theory, i thought i might just detach the fuel line from the tank to the motor and drop in in an external tank - and then see if motor runs correctly. Is this feasible? the tank works on siphon pressure from the vacuum from the motor and fuel pump, correct?

Any other thoughts appreciated!
 

JayDoc

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so i didnt get much feed back on the above post, but i think i was able to figure out online that the attachments are correct. however, the engine is still starving for fuel. i think the tank may have a blockage. what's the best way to clean out the tank short of ripping it out and putting a new one in?

Also, in order to test my theory, i thought i might just detach the fuel line from the tank to the motor and drop in in an external tank - and then see if motor runs correctly. Is this feasible? the tank works on siphon pressure from the vacuum from the motor and fuel pump, correct?

Any other thoughts appreciated!
If you want to rule out the tank as the source you can put your intake fuel line into a portable gas can - make sure the fuel pump is between the can and the engine of course - if the problem persists then the issue is closer to the engine.
Someone else mentioned checking/replacing the inline fuel filters, I'd also consider replacing the electric fuel pump.
 
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Thanks. I'll try the external tank thing. BTW- i have a mechanical pump as pictured towards the top of this thread. is there another electric fuel pump somewhere in the system that i dont know about?
 

JayDoc

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Thanks. I'll try the external tank thing. BTW- i have a mechanical pump as pictured towards the top of this thread. is there another electric fuel pump somewhere in the system that i dont know about?
Ah, maybe I misread. The PO replaced the mechanical pump? Didn't add an electric? Then no, a stock 40 doesn't have an electric pump but I and many others have added one.
 
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I have an earlier tank, so it may be different; My tank feeds the fuel pump via the port at the center of the tank. (Left circle in your picture).

If your research is correct, and the lower port is your feed, I would think you should have fuel flowing out of the hose in that picture (if there is fuel in the tank). Maybe give that hose a short burst from an air compressor….
 
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i have very little confidence my research is correct. fuel barely drips out of that bottom outlet with the hose detached (and there is plenty of fuel in tank). but, fuel is getting to the engine somehow. i figured the vacuum from the engine and the fuel pump sucks it out when the hose is attached [?] so maybe i should reverse the hoses and see what happens[?]
 
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You can try. Someone may chime in who know’s that tank better.

I may have missed it, but what would be the reason the line could be switched? Was the tank serviced or new lines put in?


BTW (slightly OT):
One thing I see a lot of people do is pumping the accelerator to get fuel into the float bowl.

Carburetors don’t work that way.
Abbreviated workings-
• The fuel pump provides fuel to the carburetor (the float bowl).
•The float bowl provides fuel for all circuits; Idle, transition (accelerator), and main.

The accelerator (pump) pumps fuel into the air horn from the float bowl. Simply, if the float bowl is empty, you’re only pumping air. You are not pumping fuel into the carburetor / float bowl. That is the job of the fuel pump.

If you don’t see fuel in the bowl using the sight glass (working your way back to the tank):
You have a
•stuck or out of adjustment float
•stuck or clogged float needle
•bad fuel pump
•clogged fuel filter
•clogged tank

•or a fuel line blockage somewhere along the way
 
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You can try. Someone may chime in who know’s that tank better.

I may have missed it, but what would be the reason the line could be switched? Was the tank serviced or new lines put in?


BTW (slightly OT):
One thing I see a lot of people do is pumping the accelerator to get fuel into the float bowl.

Carburetors don’t work that way.
Abbreviated workings-
• The fuel pump provides fuel to the carburetor (the float bowl).
•The float bowl provides fuel for all circuits; Idle, transition (accelerator), and main.

The accelerator (pump) pumps fuel into the air horn from the float bowl. Simply, if the float bowl is empty, you’re only pumping air. You are not pumping fuel into the carburetor / float bowl. That is the job of the fuel pump.

If you don’t see fuel in the bowl using the sight glass (working your way back to the tank):
You have a
•stuck or out of adjustment float
•stuck or clogged float needle
•bad fuel pump
•clogged fuel filter
•clogged tank

•or a fuel line blockage somewhere along the way
very helpful info! Thanks!

Yes, the PO changed out the fuel lines (the black flexible hose) before i purchased - so maybe they got swapped.[?] Also, a new mechanical fuel pump was installed by PO.
And i just put a new fuel filter on which did not change the situation.

Question- should the fuel in the bowl go down when accelerating, or should the fuel pressure keep it level? when i'm at idle, its level in the window, then when I push the accelerator in the driveway it goes down. when it stalls, the window is empty.
 
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very helpful info! Thanks!

Yes, the PO changed out the fuel lines (the black flexible hose) before i purchased - so maybe they got swapped.[?] Also, a new mechanical fuel pump was installed by PO.
And i just put a new fuel filter on which did not change the situation.

Question- should the fuel in the bowl go down when accelerating, or should the fuel pressure keep it level? when i'm at idle, its level in the window, then when I push the accelerator in the driveway it goes down. when it stalls, the window is empty.
The fuel level should stay relatively level.
As the fuel level drops, the float lowers and opens up the flow of fuel from the pump. If it is not filling up, you have an issue up stream, starting with the float itself.
 

Pighead

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There might be a very small screen sock, just below the fuel inlet on the top corner of the carb.
Between the fuel inlet and the needle valve. Eyeball that and make sure it's clear, if it's there.
 
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Major breakthrough! Unhooked the fuel line from the tank and dropped it into an external tank and I’m up and running! Now to figure out how to clean out the tank or whether I need to replace!

Thanks to all for the advice!
 

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