need help
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need help
I bought a 1979 f250 with a 351m about a year ago. rebuilt the motor and put it back in the truck. now it will start but only for 5 seconds and die out. if fully choked out will stay running but at high idle. can't figure this out went through vacuum line. just had the carburetor rebuilt by a kit. ran before I pulled motor. the carburetor is a 2 barrel motor craft.if I let it idle at the high rpm it comes down but if I open the choke any it will die.
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help
the motor is a 351m with a automatic transmission. with a stock rebuild. took it apart and put new seals in. replaced piston rings all good. it is getting fuel has a electric fuel pump. fresh fuel out of can. when it is fully choked it smokes a lot. i bought a junk yard carburetor to see if it was my carb but same problem. put the rebuilt one back on and started it up choked it out and let it warm up at the high RPM started to drop in RPMS but still will die if open the butterfly at all.
Posting Guru
Joined: Nov 2011
Posts: 1,302
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From: Burlington, WI
Are you sure you have all the vacuum lines plugged in correctly?
Sounds like you're getting enough gas to the carb if it can high idle with the choke closed.
Does the carb fit the manifold (square bore vs spread bore if it's a 4bbl)?
What model carb do you have on it now? Did you rebuild the original carb yourself, have a shop do it, or buy a *shudders* reman carb?
I've never had good luck with remanufactured carbs on any of my cars that Ive owned. Theyre all usually assembled in Japan by a 12 year old named Ping who likely can't speak English. Occasionally you get a good one don't get me wrong, but many are filled with issues.
Junkyard carbs are a hit and miss usually as well because you don't know how long they've been sitting, what their history is, what their settings are, etc.
I would be inclined to look for a vacuum leak...and a big one at that. Either that or maybe something in your carb is still plugged up with gunk.
What color is the smoke?
What's the history of the engine (reason for rebuild, etc)?
Sounds like you're getting enough gas to the carb if it can high idle with the choke closed.
Does the carb fit the manifold (square bore vs spread bore if it's a 4bbl)?
What model carb do you have on it now? Did you rebuild the original carb yourself, have a shop do it, or buy a *shudders* reman carb?
I've never had good luck with remanufactured carbs on any of my cars that Ive owned. Theyre all usually assembled in Japan by a 12 year old named Ping who likely can't speak English. Occasionally you get a good one don't get me wrong, but many are filled with issues.
Junkyard carbs are a hit and miss usually as well because you don't know how long they've been sitting, what their history is, what their settings are, etc.
I would be inclined to look for a vacuum leak...and a big one at that. Either that or maybe something in your carb is still plugged up with gunk.
What color is the smoke?
What's the history of the engine (reason for rebuild, etc)?
Cargo Master
Joined: Nov 2011
Posts: 3,354
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From: Great American SouthWest
Sounds like a big vacuum leak - one you should be able to hear the "hiss". perhaps the big connector at the rear base of the carb or the vacuum tree.
You could try pulling all the hoses off the tree, and capping those connectors. Then you'd only have the couple on the carb. But I'm guessing the big vacuum connector in the back - it's hard to see, as it's under the carb and in the back.
You could try pulling all the hoses off the tree, and capping those connectors. Then you'd only have the couple on the carb. But I'm guessing the big vacuum connector in the back - it's hard to see, as it's under the carb and in the back.
Fleet Mechanic
Joined: Feb 2004
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From: River Valley AR
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I just honed the cylinders. also it is the original carburetor Motorcraft 2 barrel. and is white but inside of exhaust pipe is black. the reason I rebuilt the motor was I had to reseal and I wanted to put headers on. and the manifolds where stuck on so I figured I have to pull half the motor apart why not just change them out of the vehicle.
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Fleet Mechanic
Joined: Feb 2004
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From: River Valley AR
I've been on several forums for a long time. You have to ask to know that the basics are covered.
Have you tried to pinch off or plug any vacuum connections? Have you tried to unplug any?If an engine is running lean and you unplug a vacuum hose, it may die or spit and sputter. If it's running rich, it may run better or faster.
I agree with the other posts, vacuum leaks need to be investigated. A vacuum gauge can help. Like papa bear said, check for big leaks. Just because it's capped doesn't mean the cap is good, or that the fitting it's on isn't leaking.
Have you tried to pinch off or plug any vacuum connections? Have you tried to unplug any?If an engine is running lean and you unplug a vacuum hose, it may die or spit and sputter. If it's running rich, it may run better or faster.
I agree with the other posts, vacuum leaks need to be investigated. A vacuum gauge can help. Like papa bear said, check for big leaks. Just because it's capped doesn't mean the cap is good, or that the fitting it's on isn't leaking.
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