Cutting out on acceleration
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Senior User
Joined: Nov 2000
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From: sunny san diego
Cutting out on acceleration
OK...1985 F250 460 C6....Runs perfect around town except for a slight surge around a steady 40 mph, but merging on to freeway it will start to loose power, pop 1 or 2 times through the carb, sputter, die, sputter, ect. Exit off ramp and all is well again. Does it on front and rear tank so fuel pump failure possible but not likely (?). Here's what I have checked:
-Float levels OK
-Plugs and wires less than 1 year old (not the cheap stuff)
-replaced Duraspark with a spare good one, no change.
-all vacuum hoses good, no leaks
- vacuum at idle 20-21
I'm at a loss...............
-Float levels OK
-Plugs and wires less than 1 year old (not the cheap stuff)
-replaced Duraspark with a spare good one, no change.
-all vacuum hoses good, no leaks
- vacuum at idle 20-21
I'm at a loss...............
Thread Starter
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Senior User
Joined: Nov 2000
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From: sunny san diego
Timing spot on, vacuum advance OK, no leaks. I rebuilt the carb myself about 2 years ago and consider myself somewhat of an expert on the 4180, so I doubt seriously if there is a problem with that. I suspect the ignition module, coil, or possibly the fuel pumps even though I'm not convinced they are going bad.
Cargo Master
Joined: Nov 2010
Posts: 3,244
Likes: 40
Checked for vapor lock and or too small of a fuel line/carb?
ETA noted that you are running a 4180, so unless your motor is hotrodded those things should be fine. One thing I have heard about these carbs is that the powervalves are blown to busting on a back fire....
ETA noted that you are running a 4180, so unless your motor is hotrodded those things should be fine. One thing I have heard about these carbs is that the powervalves are blown to busting on a back fire....
Posting Guru
Joined: Jun 2009
Posts: 1,509
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From: Wagener, SC
I dunno. The thing is a relatively sustained higher RPM is what's causing your issue. Kinda sounds like a fuel starving issue. Maybe you have a kink in your line that causing the carb to be pulled dry under demand?
You've checked everything else that's fuel related... Is it ONLY under load, or can you duplicate the issue by holding a high RPM for a few in your driveway?
Have you checked your coil, module, and pickup? There is more of a demand on your ignition parts at higher RPM.
I'm just throwing some things out there...
You've checked everything else that's fuel related... Is it ONLY under load, or can you duplicate the issue by holding a high RPM for a few in your driveway?
Have you checked your coil, module, and pickup? There is more of a demand on your ignition parts at higher RPM.
I'm just throwing some things out there...
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Elder User
Joined: Apr 2009
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back idle vacuum down to around 17-19 and see if that helps. Timing might be a bit high causing a misfire or detonation at part / full throttle. I would start at 17 then drive it, if it acts ok got to 18, repeat until symptoms return then back it back off.
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Thread Starter
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Senior User
Joined: Nov 2000
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From: sunny san diego
I don't want use the hit and miss method by simply replacing parts like some mechanics do and still have a problem, but I appreciate all of the suggestions. The problem is beyond the scope of my abilities.........to the shop it goes today and I will post up. Thanks all
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Senior User
Joined: Nov 2000
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From: sunny san diego
Mine has electric fuel pumps in each tank. It doesn't matter which tank I use, it still cuts out. I don't see how both pumps could go bad at the same time, but they are original and 25 years old, so 
Elder User
Joined: Apr 2009
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tweeking timing / idle vaccum is free...My 302 and 300 both acted up like that with that much vacuum at idle. Timing was advanced way too far.
Senior User
Joined: Dec 2010
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From: Strasburg, Va.
On the front of the carb itself is a mechanical pump that is used for aceelleration only.
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Joined: Jul 2011
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From: Columbus
They have actually lasted that long?
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Senior User
Joined: Nov 2000
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From: sunny san diego
That's right............I was careful never to let the fuel level drop below 1/4. Lots of peeps do that and then wonder why the fuel pump goes bad so soon.