Carb problem/question
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Senior User
Joined: May 2007
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From: Laurel, MT
Carb problem/question
Searched a bit but found little...:
My 250 turns over, but won't start. I move the throttle linkage and I hear no squirt of fuel going into the carb. I pour gas in the carb and it starts and runs fine - but occasionally will stall out if the RPMs drop. But I let it sit for a day or two and the same thing occurs. Do I have a problem with my fuel pump? Or maybe a check valve? I installed a manual choke and it is closed when I attempt to start it.
Seems like my initial fuel pressure goes away...I'm running the stock MC carb setup - on a 1972 190 swap. I recently replaced the accelerator pump parts on the front of the carb. New battery. Any suggestions?
My 250 turns over, but won't start. I move the throttle linkage and I hear no squirt of fuel going into the carb. I pour gas in the carb and it starts and runs fine - but occasionally will stall out if the RPMs drop. But I let it sit for a day or two and the same thing occurs. Do I have a problem with my fuel pump? Or maybe a check valve? I installed a manual choke and it is closed when I attempt to start it.
Seems like my initial fuel pressure goes away...I'm running the stock MC carb setup - on a 1972 190 swap. I recently replaced the accelerator pump parts on the front of the carb. New battery. Any suggestions?
Post Fiend
Joined: Jul 2006
Posts: 6,948
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Fuel starvation could be a supply problem, like a bad pump, or a stuck needle and seat, stuck float.
You can loosten the supply line, and crank the engine (from under th hood with ignition off. Done at the solenoid) to verify pump operation. If you get a decent supply of gas (you will spill, so be carefull) then you can rule out the pump, and concentrate your troubleshoting on the carb. Really sounds like a simple stuck float that is restricting the fuel flow.
The fact that the accelerator pump does not squirt is an indication of an empty bowl.
You can loosten the supply line, and crank the engine (from under th hood with ignition off. Done at the solenoid) to verify pump operation. If you get a decent supply of gas (you will spill, so be carefull) then you can rule out the pump, and concentrate your troubleshoting on the carb. Really sounds like a simple stuck float that is restricting the fuel flow.
The fact that the accelerator pump does not squirt is an indication of an empty bowl.
New User
Joined: Jan 2008
Posts: 0
Likes: 24
Gasoline evaporates.
Also fuel can be sucked back ot leak down the line toward the pump.
My one truck sits so long between starts and runs I always squirt some fuel before I even crank it.... this way it will fire up at first crank.
Look for leaking rubber line and/or fuel evaporation
Also fuel can be sucked back ot leak down the line toward the pump.
My one truck sits so long between starts and runs I always squirt some fuel before I even crank it.... this way it will fire up at first crank.
Look for leaking rubber line and/or fuel evaporation
Thread Starter
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Senior User
Joined: May 2007
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From: Laurel, MT
Originally Posted by 75F350
Fuel starvation could be a supply problem, like a bad pump, or a stuck needle and seat, stuck float.
You can loosten the supply line, and crank the engine (from under th hood with ignition off. Done at the solenoid) to verify pump operation. If you get a decent supply of gas (you will spill, so be carefull) then you can rule out the pump, and concentrate your troubleshoting on the carb. Really sounds like a simple stuck float that is restricting the fuel flow.
The fact that the accelerator pump does not squirt is an indication of an empty bowl.
You can loosten the supply line, and crank the engine (from under th hood with ignition off. Done at the solenoid) to verify pump operation. If you get a decent supply of gas (you will spill, so be carefull) then you can rule out the pump, and concentrate your troubleshoting on the carb. Really sounds like a simple stuck float that is restricting the fuel flow.
The fact that the accelerator pump does not squirt is an indication of an empty bowl.
Mil1ion: I can see a couple of weeks maybe, but I'm talking like a day or two. Gets annoying when I need to move it from the street to the driveway. Besides, if the fuel evaps, the pump should kick enough up to fill the bowl after a few seconds of cranking, correct? No leaks...I should/would see it in the driveway...all I know that leaks is the power assist control valve (another problem).
Post Fiend
Joined: Jul 2006
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Forcing fuel the oposite direction is pretty difficult to do. Now It seems logical that the pump is working well since after you prime the carb the thing stays running and will start again. This would indicate that the fuel in the bowl is draining, or discharging, probably into the intake manifold.
This may take a while, but once you get it running again, and can start the truck with repeatability. Remove the air cleaner and open the choke horn. Wedge it wide open if you have to with a screwdriver or something so you can see doun the troat of the carb. Then check to see if there is any fuel dripping into the venturis.
You may not have a supply problem, you may just have a needle that is not stopping the fuel flow when there is no demand. Since the pressure is still in the line, it could be leaking gas into the carb, and if the float is set too high, the needle may never be closing. After it sits, the little bit of gas drains into the engine, and evaporates leaving a dry bowl. This would explain your symptoms. Might not be right, but for now, it is the best I have got. Lol.
Sounds like it could be the case.
Again, bad needle and seat, or float problem.
This may take a while, but once you get it running again, and can start the truck with repeatability. Remove the air cleaner and open the choke horn. Wedge it wide open if you have to with a screwdriver or something so you can see doun the troat of the carb. Then check to see if there is any fuel dripping into the venturis.
You may not have a supply problem, you may just have a needle that is not stopping the fuel flow when there is no demand. Since the pressure is still in the line, it could be leaking gas into the carb, and if the float is set too high, the needle may never be closing. After it sits, the little bit of gas drains into the engine, and evaporates leaving a dry bowl. This would explain your symptoms. Might not be right, but for now, it is the best I have got. Lol.
Sounds like it could be the case.
Again, bad needle and seat, or float problem.
Junior User
Joined: Jun 2003
Posts: 94
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From: Arizona
my 78 350 same issue
my 78 350 has same issue, carb needs good cleaning or partial rebuild, and I have cracked filler hoses on rear tank, all gas leaks back into system not onto ground, one shot of gas in carb and VROOOOM no worries just added it to my morning routing, shot of coffe for me shot of gas for truck! lol until i can afford the other stuff, good luck and keep on truckin!
Postmaster
Joined: Aug 2000
Posts: 3,312
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From: Eldorado Ca. USA
I had the same problem. Here was where my fuel was going.
Take the carb off the truck, put it on the bench in a way you can see where any gas is leaking out. Fill it with fuel up to about the needle and seat, and keep an eye on it. While you have it apart, blow all of the passageways out with carb cleaner and air. Check your powervalve cover plate, make sure it is not warped, and that no gasoline has gotten past it. Gas should only come out after you unscrew the powervalve, not take the cover off. I would also check your oil, smell it for gasoline, and the proper level. If the oil level is rising, you for sure have a problem.
Take the carb off the truck, put it on the bench in a way you can see where any gas is leaking out. Fill it with fuel up to about the needle and seat, and keep an eye on it. While you have it apart, blow all of the passageways out with carb cleaner and air. Check your powervalve cover plate, make sure it is not warped, and that no gasoline has gotten past it. Gas should only come out after you unscrew the powervalve, not take the cover off. I would also check your oil, smell it for gasoline, and the proper level. If the oil level is rising, you for sure have a problem.
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From: Laurel, MT
Wow thanks guys - i will pull the carb and do what you suggest. All of that makes sense - the thing did sit for a while, so it may be varnished up pretty good. Maybe a rebuild kit?
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Postmaster
Joined: Aug 2000
Posts: 3,312
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From: Eldorado Ca. USA
I re-read your post, you say you are running a '72 190 with the Motorcraft carb? If you really meant 190, then I have no clue what carb you are running, but if you made a typo and meant 390, then that makes better sense.
How much cranking does it take to get the truck to start?
How much cranking does it take to get the truck to start?
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Senior User
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From: Laurel, MT
Sorry that should be 390 of course. slipped I guess. How much cranking? Till the battery dies...
I have to pour fuel down the carb for it to even stutter. But again, after it starts and runs for a minute it will continue to start up fine until parked. Until the next day or so when I have to do the same thing again.
I have to pour fuel down the carb for it to even stutter. But again, after it starts and runs for a minute it will continue to start up fine until parked. Until the next day or so when I have to do the same thing again.
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