Need Help
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Joined: Sep 2012
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From: Tularosa NM
Need Help
I recently purchased a 73 L48. Sometime ago, it started to stumble at highway speeds. It progressively got worse. Now, it will no longer maintain highway speeds and will stall while driving. I can only describe the symptom as like the fuel is shut off. While driving it, it loses power and the RPM's will drop about 500 rpm. Getting more on the pedal may get you to maintain about 35 MPH. If you pump the accelerator, it may come back. If not, it will do this until it stalls. It usually takes a few minutes until it will crank back up. Until then, it just turns over. It does have a spark when this happens. Like I said, I recently purchased it. It LOOKS like it has a new fuel tank. I have replaced the fuel pump, filter and even a brand new carb. Problem is still there. I am going to check the fuel lines but from what I see, they look fairly new. Does anyone have any ideas as to what it may be? Any help would be GREATLY appreciated as this has been going on for some time now
Burning Brakes
Joined: Jul 2012
Posts: 980
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From: West Hartford CT
Air Filter?
I have a 73 SB 350. With a stalling engine I have seen that if the air is limited the engine will choke out as it starts to lack for air I assume the air filter is clean and clear but if you haven't checked that's an easy one to look for..
Another suggestion would be to drain that gas tank even though its unlikely that you have bad gas blocking the lines, pump, or filter.
Third suggestion is to see if you have a vented fuel cap or not. As some folks block off the charcoal canister and it may cause the system to starve for air as the intake calls for more. A vented fuel cap allows for make up air into the tank and relieve the vacuum that can be created.
Good luck
Another suggestion would be to drain that gas tank even though its unlikely that you have bad gas blocking the lines, pump, or filter.
Third suggestion is to see if you have a vented fuel cap or not. As some folks block off the charcoal canister and it may cause the system to starve for air as the intake calls for more. A vented fuel cap allows for make up air into the tank and relieve the vacuum that can be created.
Good luck
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
If your charcoal canister is hooked up and working properly, you should keep a non-vented gas cap but a temporary switch to a vented cap (or maybe a short careful drive with the cap off) will let you know if you have a tank venting problem.
Is your fuel return line connected and operating properly?
Check carefully for another fuel filter installed by the previous owner and hidden from normal view. I had the exact symptoms as you on an old pickup I bought one time and after a lot of wasted effort discovered a second old fuel filter hidden underneath that was clogged and needed to be removed.
Peek in the tank and see if you can see the sock filter on the fuel pickup. If it looks like it is clogged, you may need to clean or replace it.
Make sure the float(s) in the carb is set properly.
DC
Is your fuel return line connected and operating properly?
Check carefully for another fuel filter installed by the previous owner and hidden from normal view. I had the exact symptoms as you on an old pickup I bought one time and after a lot of wasted effort discovered a second old fuel filter hidden underneath that was clogged and needed to be removed.
Peek in the tank and see if you can see the sock filter on the fuel pickup. If it looks like it is clogged, you may need to clean or replace it.
Make sure the float(s) in the carb is set properly.
DC
Melting Slicks
Joined: Mar 2007
Posts: 2,520
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From: Hinckley OH
You can check to see if you need a vented gas cap by running the car until it stalls then opening the gas cap. If you hear the air getting sucked in and/or you can start the car after opening the cap, that's it. You might need to crank the engine for about 10 seconds to get gas to the carb.
The other thing is that someone may have replaced the "S" shaped hoses from the fuel lines to the fuel pump with regular fuel hose. If that's the case, the hoses can collapse and restrict fuel flow. They might be OK when cold but become softer as they heat up which allows the suction from the fuel pump to collapse them.
The other thing I would do is look down the carb throat and push the accelerator linkage after it stalls. If you don't see two squirts of fuel that will at least confirm that it's a fuel delivery problem.
A restricted exhaust is the only other thing I can think of that might cause those symptoms. If you still have a heat riser between the exhaust manifold and the exhaust pipe, make sure it is able to open.
Good luck.
The other thing is that someone may have replaced the "S" shaped hoses from the fuel lines to the fuel pump with regular fuel hose. If that's the case, the hoses can collapse and restrict fuel flow. They might be OK when cold but become softer as they heat up which allows the suction from the fuel pump to collapse them.
The other thing I would do is look down the carb throat and push the accelerator linkage after it stalls. If you don't see two squirts of fuel that will at least confirm that it's a fuel delivery problem.
A restricted exhaust is the only other thing I can think of that might cause those symptoms. If you still have a heat riser between the exhaust manifold and the exhaust pipe, make sure it is able to open.
Good luck.
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Joined: Sep 2012
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From: Tularosa NM
First, thanks for all your inputs. I have checked the fuel cap and even ran the vehicle while the cap was off. Still had the same problem so I have ruled that out. Problem also occured while I had the air filter off.
Fuel return is connected, working properly??? Will check. Will check inside the tank and for another filter. Will also check fuel lines. I hope I find this soon. Any other suggestions would be appreciated...
Fuel return is connected, working properly??? Will check. Will check inside the tank and for another filter. Will also check fuel lines. I hope I find this soon. Any other suggestions would be appreciated...
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Joined: Sep 2012
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From: Tularosa NM
OK, found an aftermarket fuel filter and replaced it. Still had the same problem. Looked at the sock filter and ripped it in two. Then I found what I think is my problem. A kinked fuel line between the fuel tube and the fuel pump. Will get that replaced today. So now, Where can I get a replacement fuel sock for the pickup in the fuel tank and more importantly, how do i get to it to remove whats left and to install the new one???
Melting Slicks
Joined: Apr 2001
Posts: 2,030
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From: Lubbock Texas
As a Plan B, you could install another filter just outside the tank. But, for this filter you don't really want a regular filter. Look for one called a "pre-filter" - the efi installations often use them before the electric pumps. You basically just want something that keeps larger particles from getting to the fuel pump without making the fuel pump suck hard through a normal filter.
DC
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From: Shearwater Nova Scotia
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Joined: Sep 2012
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From: Tularosa NM
Since a screw on fuel filter/water separator is installed just out side on the tank before the fuel pump and I have a inline fuel filter before the carb, should I be concerned about the sock not being installed?
Melting Slicks
Joined: Apr 2001
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From: Lubbock Texas
DC
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Joined: Sep 2012
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From: Tularosa NM
Thank you all for the help. Turned out the problem was the fuel line to the fuel pump. Next job will be to get the sock back on but with the external filter, I am not going to try and get it done "tomorrow", just soon. Course, found something else wrong, but that will be a different thread. Again, thank you all for the help!!!