Hesitation
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From: Wingo, Ky
Hesitation
Past week or so I have noticed while going down the road in my F100 302 if I accelerate quickly the truck will hesitate or stumble for a second. Revs up fine when in neutral/park. It didn't use to do this.
Things that I have done in the past week that might have something to do with it.
1.Hot air choke was plugged off because I didn't have a tube ran. Ran and bent new tubing and hooked it up and is working properly. Choke is wide open after it is warmed up.
2. I played with the idle mixture screws some, maybe I didn't set them as good as I thought. I need to pick me up a vacuum guage.
3.Removed stock style filter from carb. Replaced with a fitting that screwed into carb so I could but a hose on it and install clear filter. Maybe the fitting I used is screwing into the carb to far and disrupting something? Filter is constantly full, so pump is good.
Only thing else I can think of is points need adjusting. I put them in new and they now have close to 3,000 miles on them.
Things that I have done in the past week that might have something to do with it.
1.Hot air choke was plugged off because I didn't have a tube ran. Ran and bent new tubing and hooked it up and is working properly. Choke is wide open after it is warmed up.
2. I played with the idle mixture screws some, maybe I didn't set them as good as I thought. I need to pick me up a vacuum guage.
3.Removed stock style filter from carb. Replaced with a fitting that screwed into carb so I could but a hose on it and install clear filter. Maybe the fitting I used is screwing into the carb to far and disrupting something? Filter is constantly full, so pump is good.
Only thing else I can think of is points need adjusting. I put them in new and they now have close to 3,000 miles on them.
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From: Wingo, Ky
I bought me a vacuum gauge today. I guess now I will be re-tuning all three of my trucks and all my friend's trucks.
I'm going to start off with the 73 F100 302 since thats what the post is about.
Will hooking into the pcv valve port on the carb be a good place?
Have engine to operating temp. Turn each screw in gently all the way then back them off equally till the engine will idle. Then continue to back the screws out equally till highest vacuum reading is acheived. Would this be the correct procedure? Thanks in advance.
I'm going to start off with the 73 F100 302 since thats what the post is about.
Will hooking into the pcv valve port on the carb be a good place?
Have engine to operating temp. Turn each screw in gently all the way then back them off equally till the engine will idle. Then continue to back the screws out equally till highest vacuum reading is acheived. Would this be the correct procedure? Thanks in advance.
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Joined: Jun 2008
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From: Duncan B.C.
Try this link. It has a whole bunch of stuff you can diagnose with a vacuum guage and instructions on how to do it.
(check out "scenario 15")
How to Use and Interpret a Vacuum Gauge
(check out "scenario 15")
How to Use and Interpret a Vacuum Gauge
Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
Will hooking into the pcv valve port on the carb be a good place?
Have engine to operating temp. Turn each screw in gently all the way then back them off equally till the engine will idle. Then continue to back the screws out equally till highest vacuum reading is acheived. Would this be the correct procedure?
Have engine to operating temp. Turn each screw in gently all the way then back them off equally till the engine will idle. Then continue to back the screws out equally till highest vacuum reading is acheived. Would this be the correct procedure?
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From: Wingo, Ky
Runs good but while going down the road if I quickly depress the gas it will stumble( I guess I could describe it as a hicup) a second, then catch up and be fine.
Feels like a four barrel with the secondaries not set properly kinda, giving you a kick that sets you back in the seat.
I will set mixture screws then get back with yall.
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MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Sounds like a faulty accelerator pump. Air is lighter than fuel per unit volume, therefore when you get on the accelerator, the fuel in the carburetor can't travel as quickly as the inrush of air through the throat of the carburetor. This is solved through the use of an accelerator pump.
The stock 2-barrel carburetor also has an idle transfer circuit to transition the fuel mixture between idle and open throttle, as shown by two small vertical slots in the throttle bores of the carburetor. If these are obstructed, you will see symptoms which are similar to those you are seeing.
The stock 2-barrel carburetor also has an idle transfer circuit to transition the fuel mixture between idle and open throttle, as shown by two small vertical slots in the throttle bores of the carburetor. If these are obstructed, you will see symptoms which are similar to those you are seeing.
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From: Wingo, Ky
The carb has only been on the truck about 3 months. Its a rebuild unit from the parts store. New fuel pump, all rubber line replaced, clear inline filter.
It didn't have the slight stumble till about 3 or 4 weeks ago. Something that I did do to it before I started notcing the stumble was play around with the mixture screws. Thats why I decided to get a vacuum gauge and set them right and go from there.
Surely it hasnt got trash in it, filter is clean as can be. And surely the accelerator pump isn't faulty, but could be.
It didn't have the slight stumble till about 3 or 4 weeks ago. Something that I did do to it before I started notcing the stumble was play around with the mixture screws. Thats why I decided to get a vacuum gauge and set them right and go from there.
Surely it hasnt got trash in it, filter is clean as can be. And surely the accelerator pump isn't faulty, but could be.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
It's quite possible the mixture screws could be the problem as well, because if the mixture chemistry at idle is off, the condition can be exacerbated as the throttle is opened. Adjust the mixture screws such that the vacuum gauge pegs, let us know what happens.
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From: Wingo, Ky
I was just looking through my manual and it says for a 73 F100 with 302 and auto tranny that accelerator pump rod should be on inboard hole and and in notch B(2nd from bottom). It says during winter use increase stroke by moving to notch C or D(the higher notches). I will take a look at all this stuff tommorow and get back.
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Joined: Jan 2010
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From: bellevue ne
i have a 2000 ford f250 with the 5.4, doing almost the same thing. i was wondering if it could be the beginning of a fuel filter going bad? please let me know, i just bought the truck like two weeks ago.
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From: Wingo, Ky
Well it was 25 degrees here today but I put my coveralls and everything on and went and and messed with the truck. I cranked it up let it run till it was fully warmed up.
Hooked up the vacuum gauge and adjusted everything and it is just a hair short of pulling 21. It was setting on about 20 and a half. Im not sure if it was at the correct idle or not(need to get a tach). I actually think its probably a little to low.
After doing this I could really hear the difference when it picked up and idles alot better.
Hooked up the vacuum gauge and adjusted everything and it is just a hair short of pulling 21. It was setting on about 20 and a half. Im not sure if it was at the correct idle or not(need to get a tach). I actually think its probably a little to low.
After doing this I could really hear the difference when it picked up and idles alot better.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
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