Hesitation issue
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Junior User
Joined: Sep 2009
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From: CT
Hesitation issue
Hi folks, I have a recurring issue with my '48 F-3 that I would like to get sorted once and for all. Seems to happen every year when the cold weather hits--an off-idle stumble where the throttle response is interrupted for about a second, then the rpms "catch up" all at once with a perceptible jerk, and then normal operation resumes until my driving next brings me back to deceleration, and then again.
The engine is a 6-cylinder and is in tune. New points, condensor and rotor 1,000 miles ago, points set with dwell meter at 36 degrees, timing set at mark.
I'm thinking this is a carb issue, because when I run it partially choked, the problem is lessened; it ceases altogether in warm weather. This is an original Ford 1-barrel carb, with the three settings for accelerator pump set at the richest because that's where it always ran the best. Could it be the accelerator pump shot? Any thoughts to help me?
The engine is a 6-cylinder and is in tune. New points, condensor and rotor 1,000 miles ago, points set with dwell meter at 36 degrees, timing set at mark.
I'm thinking this is a carb issue, because when I run it partially choked, the problem is lessened; it ceases altogether in warm weather. This is an original Ford 1-barrel carb, with the three settings for accelerator pump set at the richest because that's where it always ran the best. Could it be the accelerator pump shot? Any thoughts to help me?
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
You're thinking correctly and troubleshooting right. But, keep in mind a lean fuel mixture is a lot harder to ignite. Consequently Richening the air/fuel mixture is an easy way to compensate for a weak ignition.
Believe Nothing
Joined: Jun 2004
Posts: 7,516
Likes: 403
From: W. Central FL.
With the engine static, turned off, look down the carburetor throat and work the throttle. You should be getting a squirt of fuel starting with the movement of the throttle and continue thru full movement of the throttle.
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Junior User
Joined: Sep 2009
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From: CT
I was thinking along the lines of weak ignition as well, and trying to figure how the cold weather component factors into things....cold air is denser than warm and the air molecules are packed closer, which I guess strengthens the air part of the A/F mix in cold weather. Thus the better response when the fuel is richened. But this only occurs coming off idle, and I'm already at the strongest setting for the accelerator shot.
BTW I have run it with the air cleaner both on and off...doesn't make any difference.
BTW I have run it with the air cleaner both on and off...doesn't make any difference.
Logistics Pro
Joined: Nov 2006
Posts: 3,679
Likes: 370
From: Fallon,NV & Bainbridge OH
I will put my Christmas money on the accelerator pump in the carb producing a weak squirt of fuel. The cold is causing something to shrink or stick, resulting in a less than adequate shot of fuel. I would check the the accelerator pump diaphragm and the check ball after doing as Ray directed.
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Junior User
Joined: Sep 2009
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From: CT
I don't own a vacuum gauge. I wonder if I should buy one. I will check the accelerator pump shot though and see if it is providing a shot throughout throttle movement. If not, I will have to remove the carb to my workbench and take it apart.
I think I replace the accelerator pump diaphram while I have things apart. I will also replace the baseplate gasket (can't remember having done this--have owned the truck since 1970) while I'm at it.
I think I replace the accelerator pump diaphram while I have things apart. I will also replace the baseplate gasket (can't remember having done this--have owned the truck since 1970) while I'm at it.
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Logistics Pro
Joined: Sep 2014
Posts: 4,920
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From: Bothell & Silverdale, WA
Vacuum gauges are invaluable. You can fine tune carburetor settings and ignition timing, check for vacuum leaks, and check for burned valves and valve lash that's too tight. And they are cheap. Some even have a fuel pump pressure scale. Don't get the type for dash mounting because they are dampened, get the large 3" hand-held dial type with various hose connections included.
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Junior User
Joined: Sep 2009
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From: CT
OK, upon inspection (in between xmas obligations) here is what I found. The accelerator pump shot is weak and not entirely consistent. Also, after having worked the throttle a couple times there is a slight but noticeable leak of gas coming from under the accelerator pump shaft.
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