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HELP stalling when decelerating / quick drop in RPMs

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Old 12-28-2015, 04:43 PM   #1
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Default HELP stalling when decelerating / quick drop in RPMs

Hey guys need some help solving this one. 86 F150 4.9L I6, carbureted + manual.

To start, I was stuck behind an accident and led me to miscalculate gas for first time. Few days later ran low/out and it died. Sure I sucked some unwanted sludge up as truck had sat some before PO started making repairs.

The truck has been running great until then, now it has started doing something it has never done before. When the rpm's drop to idle the truck will stall. It does this going down the road and you pull up to a light, stop sign or slow for a turn. The truck does restart easily and maintains idle till you let the rpm's fall rapidly. You can prevent it from stalling by feathering the throttle allowing the rpm's to drop slowly.

I replaced the old, dirty fuel filter and it's running better but problem still around. I replaced cap, rotor, plugs and wire recently after the running out of gas incident. Found a similar post in diesel forum but their 'fix' wouldn't apply here:
http://www.ford-trucks.com/forums/10...l-to-idle.html

Any thoughts / suggestions? Need to get her back out on the road!

Last edited by 86FordF150Philly; 12-28-2015 at 05:00 PM.
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Old 12-28-2015, 09:14 PM   #2
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Sound like the carburetor may need adjustment/rebuild. Which carb. are you running?
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Old 12-29-2015, 06:25 PM   #3
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Haven't been messing with a carb in a while, but it seems to me they used to come with an "anti stall dashpot" which was a little thing on the side that caught the linkage and let it close a little more slowly.
Kind of like a cushion effect so it didn't slam the throttle plates shut.
I don't know if you even have that on your truck, but it's worth a look.
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Old 12-30-2015, 11:53 AM   #4
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Quote:
Originally Posted by GhostriderI View Post
Sound like the carburetor may need adjustment/rebuild. Which carb. are you running?
Just the stock one for the year, I'm not sure how to identify it specifically
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Old 12-30-2015, 11:54 AM   #5
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Quote:
Originally Posted by Chris_1 View Post
Haven't been messing with a carb in a while, but it seems to me they used to come with an "anti stall dashpot" which was a little thing on the side that caught the linkage and let it close a little more slowly.
Kind of like a cushion effect so it didn't slam the throttle plates shut.
I don't know if you even have that on your truck, but it's worth a look.
Thanks Chris definitely a good lead, that seems to be what is happening here, do you happen to remember specifically where that was located so I can test/clean? Cheers
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Old 12-30-2015, 10:17 PM   #6
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"Anti stall dash-pot" is mounted on the carb. next to the throttle. When the throttle is closed it is touching it. To my knowledge it can be adjusted and tested, it is a screw adjustment, there is a small (about 1/8" diameter) pin sticking out touching the throttle that slows the throttle for about the last 1/8" to 1/4" depending on the length of the pin and condition of the spring inside the pot. I have seen where people thought it was useless and backed them all the way back so they don't get used and just sit there, or they use them to adjust curb idle and wonder why it will not stay set (as the pin and spring wears out). It will look something like this (I do not know which carb you have so this is as close as I can guess)
http://www.ebay.com/itm/213-W18A-Car...VWZvya&vxp=mtr

May or may not have electrical or vacuum connection

Hope this helps
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Old 12-31-2015, 02:43 AM   #7
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I actually removed my dashpot because it was worn and I haven't gotten around to replacing it yet and mine doesn't have this problem, but its worth a look.

Take a picture of your carb and post it and we can help you identify it as well as tell you if you've got the dashpot on it.
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Old 01-11-2016, 03:50 PM   #8
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Sorry for the delay finally snapped a picture, just the stock single barrel it looks like. Upped the idle a quarter turn and seems to be running better already, idling around 900 rpm or so and hasn't died like it was (so far with minimal driving tests)




Quote:
Originally Posted by GhostriderI View Post
"Anti stall dash-pot" is mounted on the carb. next to the throttle. When the throttle is closed it is touching it. To my knowledge it can be adjusted and tested, it is a screw adjustment, there is a small (about 1/8" diameter) pin sticking out touching the throttle that slows the throttle for about the last 1/8" to 1/4" depending on the length of the pin and condition of the spring inside the pot. I have seen where people thought it was useless and backed them all the way back so they don't get used and just sit there, or they use them to adjust curb idle and wonder why it will not stay set (as the pin and spring wears out). It will look something like this (I do not know which carb you have so this is as close as I can guess)
http://www.ebay.com/itm/213-W18A-Car...VWZvya&vxp=mtr

May or may not have electrical or vacuum connection

Hope this helps
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Old 01-13-2016, 12:02 AM   #9
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Quote:
Originally Posted by 86FordF150Philly View Post
Sorry for the delay finally snapped a picture, just the stock single barrel it looks like. Upped the idle a quarter turn and seems to be running better already, idling around 900 rpm or so and hasn't died like it was (so far with minimal driving tests)


Looks like a Carter. If there is a dash pod it would be where the electronic solenoid is at the bracket under the heal of your hand in the photo. Does that part touch the throttle linkage? If it does it may be to bump the idle up when the AC (if equipped) or Defroster (if you have AC) are on to compensate for the load on the engine. and (with AC)/or (no AC) to slow the throttle closing near idle
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Old 04-19-2017, 11:25 PM   #10
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Default solution?

did you ever figure out what it was my friends is doing this as well?
thanks!
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