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Generation 7 1980-1986 F150, F250, F350

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Old 08-21-2015, 06:58 PM
johnb johnb is offline
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Question bad choke?

Hi All,
I have this great truck, itís a 1984 F150 short bed with a 4.9 L 300 cu in 6 cylinder, twin tanks and an automatic transmission with Overdrive. This is the first vehicle I ever bought brand new from the Ford dealer. Last year I decided to have it redone, I had the engine rebuilt, the body repainted and the interior reupholstered. It looks great and turns heads when I am on the road. I only have two issue that my mechanic canít figure out. The first is no big deal, whenever I gas up the rear tank, it keeps shutting off the pump unless I hold the nozzle at just the right angle and donít try to fill it too fast. The second issue is driving me crazy. I have to wait until the truck is completely warmed up before I drive it or it will miss and knock and lose power when I try to give it any gas. This is real scary when I try to merge onto the freeway. Actually, it will run good when itís cold but when it starts to warm up, thatís when it gets real flaky. This is a California truck so it has all kind of emission related components attached to the carburetor and I think it may have something to do with the choke? If anyone has any thoughts on this or has an idea what may be the cause I would love to hear from you.
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File Type: jpg carb right side.jpg (445.7 KB, 7 views)
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Old 08-23-2015, 07:25 PM
jebadiah04 jebadiah04 is offline
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the choke as 2 functions, and the best way to see if its working is this.

If the motor is cold, is the choke closed?

If the motor is hot, is the choke open?

If so, then you are good.

But clanking and rattling under acceleration...i would put a crisp 1 dollar bill on it that you have a timing issue. And to further elaborate i would guess its not retarding under thottle. However, if i remember right, these years (the last of the carbs) had some wierd computer controlled stuff that advanced the timing based on the carburetor and such. I dont fully understand how it works, but i do know if you swap out a stock carb for aftermarket you also have to swap out the distributor to a vac advance model. Because of the same reasons you are having, wont retard under throttle. So that leads me to believe that you may actually have carb issues, but i wouldnt rule out distributor issue either.

Other possible causes could be a lean condition. which would be easily diagnosed by pulling a plug out and checking what color it is. Pull either plug 2 or plug 5, since 1 and 6 run a little lean and 3 and 4 run a little rich anyways. make sure its a nice clean brown color, not wet or black or white

The hard to fill gas tanks is usually caused by 1 of 2 things, plugged or kinked vent, or evap canister.
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Old 08-24-2015, 12:56 AM
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Ozzie Ozzie is offline
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California has vapor recovery units on their fuel pumps unlike many other states. When I was there, I had the same filling problem you describe with my '76 F-250. The pumps without this feature elsewhere were much better to use. As a matter of fact, I never spilled so much fuel during the filling process as I did in CA. It's hard to understand how this helps the environment. Regarding the choke, I could never get it to work correctly on the 4350 carburetor. I changed to a manual choke. It is excellent as long as the operator understands how to use it.
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california emission, runs bad unless warmed up, yfa-1v

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