73 FE390 Carb problem
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Senior User
Joined: Aug 2013
Posts: 133
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From: San Diego
73 FE390 Carb problem
Hey guys,
I'm hoping this is a simple question... yesterday my truck started running rough as I left work heading home. Engine wouldn't run, seemed like flooding. With the pedal held to the floor I could get it to start but it'd bog down and die if I took my foot off full throttle. I eventually made it home after a rough 5 miles, but the carb is misbehaving badly.
Today while cranking it over, I noticed there's fuel spewing out of the small nozzle in front of the carb right by the butterfly valve, enough to make a deep puddle on the manifold. That's after only a few turns cranking it over.
I'm not that familiar with these old carbs, anyone have a suggestions what might be causing it? Stuck float? Carb totally fuqued? Can I use one of those cheapo replacement carbs from Kragen or Autozone?
Help!
Thanks,
John
I'm hoping this is a simple question... yesterday my truck started running rough as I left work heading home. Engine wouldn't run, seemed like flooding. With the pedal held to the floor I could get it to start but it'd bog down and die if I took my foot off full throttle. I eventually made it home after a rough 5 miles, but the carb is misbehaving badly.
Today while cranking it over, I noticed there's fuel spewing out of the small nozzle in front of the carb right by the butterfly valve, enough to make a deep puddle on the manifold. That's after only a few turns cranking it over.
I'm not that familiar with these old carbs, anyone have a suggestions what might be causing it? Stuck float? Carb totally fuqued? Can I use one of those cheapo replacement carbs from Kragen or Autozone?
Help!
Thanks,
John
Senior User
Joined: Dec 2013
Posts: 348
Likes: 4
From: Bakersfield,CA
Agree with the theory that the cause is a faulty float.
1. Sometimes the plastic floats absorb sufficient fuel to sink or loose
boyancy.
2. Sometimes the elastomer seal in the needle and seat valve is dissolved
by ethanol/gasoline mixture.
3. Sometimes a particle will get trapped in the needle and seat shut off valve and prevent fuel shut off to the bowl.
Anyone of these conditions will cause fuel to be pumped out of the bowl vent.
Some carburetor vents go directly to atmosphere and some are routed by hose to a evorative charcoal emmsions canister.
If the carburetor vent goes directly to atmosphere , fuel will be pumped out of the vent onto the intake manifold while the engine is also running rich on excessive fuel.
This the reason why the engine would only run on full throttle, to burn up the excessive fuel.
If the carburetor back fires from running too rich from excessive fuel, which is quite common, the back fire could ignite the fuel collected on the manifold.
This event happed to my 73 CJ5 Jeep with an Holley 4150 carburetor.
The gasoline fire burned up everything, except the steel parts, including the pot metal steering wheel adapter, speedometer, battery, seats, belts and melted the carburetor, spark plug wires, all wiring, cap, rotor, paint, etc.
1. Sometimes the plastic floats absorb sufficient fuel to sink or loose
boyancy.
2. Sometimes the elastomer seal in the needle and seat valve is dissolved
by ethanol/gasoline mixture.
3. Sometimes a particle will get trapped in the needle and seat shut off valve and prevent fuel shut off to the bowl.
Anyone of these conditions will cause fuel to be pumped out of the bowl vent.
Some carburetor vents go directly to atmosphere and some are routed by hose to a evorative charcoal emmsions canister.
If the carburetor vent goes directly to atmosphere , fuel will be pumped out of the vent onto the intake manifold while the engine is also running rich on excessive fuel.
This the reason why the engine would only run on full throttle, to burn up the excessive fuel.
If the carburetor back fires from running too rich from excessive fuel, which is quite common, the back fire could ignite the fuel collected on the manifold.
This event happed to my 73 CJ5 Jeep with an Holley 4150 carburetor.
The gasoline fire burned up everything, except the steel parts, including the pot metal steering wheel adapter, speedometer, battery, seats, belts and melted the carburetor, spark plug wires, all wiring, cap, rotor, paint, etc.
Thread Starter
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Senior User
Joined: Aug 2013
Posts: 133
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From: San Diego
Thanks for the info guys, I was pretty sure a stuck float was the issue. With your confirmation I went ahead and ordered a new carb to avoid any other issues with the 40+ year-old original. Got it today, so I know what;s on for Saturday....
I had a fire last year too, but that was sudden, caused by a fuel line leak onto the intake and lit up by a stray spark. Only burned my wiring and dizzy cap etc, so relatively painless fix.
I'll be back with an update once the new carb is installed.
Thanks again doods!
Update: Picked up new carb last night, pulled the old one this morning. Sat the two side-by-side to match up all the linkage parts for the kickdown etc.... Trouble.
The lever that actuates the accelerator pump came in the bag of linkage parts instead of attached to the new carb. After investigating, I find that the spindle that mounts the actuator is sheared, so I look at re-using the old one. Then I find that the screw thread is still inside the hole in the carb body!!!
I could spend hours working on pulling the old thread, but this is a brand new f'n carb! Thanks O'Reilly!
Now the replacement isn't going to arrive until Tuesday evening....
I had a fire last year too, but that was sudden, caused by a fuel line leak onto the intake and lit up by a stray spark. Only burned my wiring and dizzy cap etc, so relatively painless fix.
I'll be back with an update once the new carb is installed.
Thanks again doods!
Update: Picked up new carb last night, pulled the old one this morning. Sat the two side-by-side to match up all the linkage parts for the kickdown etc.... Trouble.
The lever that actuates the accelerator pump came in the bag of linkage parts instead of attached to the new carb. After investigating, I find that the spindle that mounts the actuator is sheared, so I look at re-using the old one. Then I find that the screw thread is still inside the hole in the carb body!!!
I could spend hours working on pulling the old thread, but this is a brand new f'n carb! Thanks O'Reilly!
Now the replacement isn't going to arrive until Tuesday evening....
Last edited by notthemaniusedtobe; Dec 6, 2014 at 03:44 PM. Reason: Update to story
Thread Starter
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Senior User
Joined: Aug 2013
Posts: 133
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From: San Diego
OK so... I went to pick up my new carb on the "promise" day of Tuesday. Surprise, surpise, O'Reilly let me down AGAIN! How I got out of there without swearing even once is beyond me. And they now know for damn sure that they've lost a 10+ year customer as soon as they complete this one last transaction...
A phone call came in on Wednesday at 8am, long before they opened, confessing that they did in fact have my carb the previous evening. Now I'm seriously twisted... Do they have employee training to become THAT incompetent?
All that said, I picked up the new carb Wednesday, installed it in about 30 mins, and the truck is running like a champ. Now I just have to swap in the electric choke, since the new carb has a cable operated choke mechanism, but my truck has a conversion kit (or came with it in 1973..?)
Thanks for the spot-on accurate diagnosis way back at the beginning though guys!
So 5 days and 1 hour (1 hour was the total labor time) to get my "stuck float" issue resolved. This was way more ****-ache than it needed to be.
A phone call came in on Wednesday at 8am, long before they opened, confessing that they did in fact have my carb the previous evening. Now I'm seriously twisted... Do they have employee training to become THAT incompetent?
All that said, I picked up the new carb Wednesday, installed it in about 30 mins, and the truck is running like a champ. Now I just have to swap in the electric choke, since the new carb has a cable operated choke mechanism, but my truck has a conversion kit (or came with it in 1973..?)
Thanks for the spot-on accurate diagnosis way back at the beginning though guys!
So 5 days and 1 hour (1 hour was the total labor time) to get my "stuck float" issue resolved. This was way more ****-ache than it needed to be.
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