Strange issue
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Tuned
Joined: Apr 2019
Posts: 310
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Strange issue
1977 F250, automatic, 460 V8..... The truck won't start on its own. It cranks just fine, but won't start until i pour a little fuel into the carburetor. After it starts, it runs fine and then will restart if i shut it off and start it again. If i try to start it the next day, it won't start. Spark is good and the fuel pump is pumping fuel. Amy ideas?
Cargo Master
Joined: Jun 2014
Posts: 2,217
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From: Central Florida
Take a quick look at the accelerator pump on the carb. Look down into the carb while you actuate the acc pump via acc linkage. You should see gas squirting into the carb. If not, replace the acc pump and these symptoms should abate. However, when the acc pump is worn out other carb sub systems may be on the verge of failure. Perhaps time for a carb rebuild.
Lead Driver
Joined: Oct 2018
Posts: 7,892
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I assume you're talking cold starts, If it won't start while you're pumping the gas the accelerator pump sure might need looked at. but if your choke is working properly you shouldn't need an accelerator pump to start it. one pump to set the choke and it should fire up and run .
Hotshot
Joined: Feb 2004
Posts: 10,834
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From: The Shenandoah Valley
Until the engine is actually running, there's not a lot of vacuum through the carburetor bores and so there is little incentive for gasoline to be crawl up through the jets & passages from the float bowl. That's where the accelerator pump helps, it kicks in raw gasoline through the shooters into the throttle bores, to enter the intake with air. That one pump to set the choke also operates the accelerator pump, causing a shot. A choke cutting off air supply way up on top can't make a rich fuel mix without fuel.
Lead Driver
Joined: Oct 2018
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Maybe on junk carbs not a properly functioning Holley. I could go pump the pedal tonight on my carbed vehicles and they'd start in a few revolutions in the morning without touching the pedal. the accelerator pump definitely does set up the instant start though, agree on that.
But the OP says he has to add gas to get it to start. but he didn't say he was pumping it, the choke isn't working correctly, and if he's pumping it and it won't start neither is the AP. need more information.
But the OP says he has to add gas to get it to start. but he didn't say he was pumping it, the choke isn't working correctly, and if he's pumping it and it won't start neither is the AP. need more information.
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Tuned
Joined: Apr 2019
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Thanks for the replies. Further info.....
I am talking about cold starts. I have done a rebuild, after which it started and ran fine.... This is a new issue. The carb in question is a Motorcraft 4350. I have tried starting with AND without pumping.... Same results. My buddy said he couldn't see any fuel squirting, but it runs fine when it's started so it must be getting fuel, correct?. We pulled the carb back off to take a look and there appears to be 2 different pumps,.... One with a diaphragm situated in the edge of the fuel bowl and another between the floats that is a cylinder with an O ring on it. The O ring didn't seem to be large enough to make contact with the wall of the chamber.
I am talking about cold starts. I have done a rebuild, after which it started and ran fine.... This is a new issue. The carb in question is a Motorcraft 4350. I have tried starting with AND without pumping.... Same results. My buddy said he couldn't see any fuel squirting, but it runs fine when it's started so it must be getting fuel, correct?. We pulled the carb back off to take a look and there appears to be 2 different pumps,.... One with a diaphragm situated in the edge of the fuel bowl and another between the floats that is a cylinder with an O ring on it. The O ring didn't seem to be large enough to make contact with the wall of the chamber.
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Lead Driver
Joined: Oct 2018
Posts: 7,892
Likes: 2,370
Just look into it and open the throttle, you should see the fuel streams when the pump is actuated. You should be noticing a hesitation and stumbling when you open the throttle if you have a pump problem. but you're correct if it runs fine after start up if's not your delivery.
Maybe ask Santa for a new 4160 this Christmas.
Maybe ask Santa for a new 4160 this Christmas.
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Thread Starter
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Tuned
Joined: Apr 2019
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So I've localized the problem. The choke plate isn't closing during my cold starts. I was going to pour fuel in the carb to start it, but figured I'd give it a try without. Took off the air cleaner, tried to set the choke by pressing the accelerator and it didn't close so i closed it with my hands and the truck started on the second try. What would cause the choke to not set? Some adjustment of die i miss something when i put the carb back together? Or am I maybe not pressing the accelerator down far enough?
Hotshot
Joined: Feb 2004
Posts: 10,834
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From: The Shenandoah Valley
Do you see a round black plastic or bakelite housing over on the passenger side of the carburetor? It has a wound up like clock spring inside it ... that uncoils as it heats up ... and when cold, it tightens up. There are three screws and a triangular round retainer ring. Up top, you'll see marks. Loosen the screws, but do not remove the screws and rotate the black round piece back and forth. Doing so should cause the choke plate to move if the throttle is held open a little. It's how you adjust a choke "rich" (more closed) ... versus ... "lean" (more open). Sounds like you need it richer?
Thread Starter
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Tuned
Joined: Apr 2019
Posts: 310
Likes: 50
Do you see a round black plastic or bakelite housing over on the passenger side of the carburetor? It has a wound up like clock spring inside it ... that uncoils as it heats up ... and when cold, it tightens up. There are three screws and a triangular round retainer ring. Up top, you'll see marks. Loosen the screws, but do not remove the screws and rotate the black round piece back and forth. Doing so should cause the choke plate to move if the throttle is held open a little. It's how you adjust a choke "rich" (more closed) ... versus ... "lean" (more open). Sounds like you need it richer?
Thread Starter
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Tuned
Joined: Apr 2019
Posts: 310
Likes: 50
I did not because it was running well before i took it off to change a leaky gasket and i thought it'd be better to not touch or adjust anything other than what was necessary. I was apparently wrong in that assumption.