84 F150 carb question
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From: Kansas City, MO
84 F150 carb question
I bought a beater 84 4x4 for work and play purposes. It has been running rich and has been backfiring on decceleration. I wanted to lean out the fuel mixture (while I wait for my buddy to bring in his vaccuum gauge to test the advance). I can't find a idle air mixture needle on the carb anywhere. It's a 351 with the Holley 4180 4bl carb. Did these carbs come from the factory without the needle? I bought a rebuild kit for it a few weeks back and the kit doesn't have a new needle in it. Any help appreciated.
Zac
Zac
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The 4180 is an emissions carb and as such has limited adjustment. The idle mixture screws are under the fuel bowl (some have a total of four screws with two under the front and two under the rear fuel bowls) and probably have caps over them to keep them from being adjusted. A rebuild kit will not have new screws.
To get the caps off you will probably have to remove the carb. Then you will have the problem of finding a way to turn the screws. They seem to take some kind of special wrench that I was unable to locate when I was attempting to adjust mine.
Based on your comments as to how it is running I suspect the power valve is blown and causing an over rich situation.
I gave up on mine and got an Edelbrock - I’m now a happy camper.
Good luck,
Mark
To get the caps off you will probably have to remove the carb. Then you will have the problem of finding a way to turn the screws. They seem to take some kind of special wrench that I was unable to locate when I was attempting to adjust mine.
Based on your comments as to how it is running I suspect the power valve is blown and causing an over rich situation.
I gave up on mine and got an Edelbrock - I’m now a happy camper.
Good luck,
Mark
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Senior User
Joined: Feb 2004
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From: Kansas City, MO
Getting a new carb is not really an option for me. This truck will primarily see use as a commuter vehicle/beater for the next 6 months. After that I plan to sell it and buy a 96 Bronco.
Rebuilding the carb is about as far as I really want to get into this thing. I have a feeling the timing advance may be non-functional or not working properly. The truck has developed an exaust leak on the right manifold. I'm pretty sure this was caused by the late firing of the cylinder burning through the gasket. But, me not so smart when it comes to diagnosing engine stuff.
As far as the power valve. What is that, where is it located, can it be fixed, and how hard is it to fix? I'm pretty much a layman here, so bear with me.
Thanks,
Zac
Rebuilding the carb is about as far as I really want to get into this thing. I have a feeling the timing advance may be non-functional or not working properly. The truck has developed an exaust leak on the right manifold. I'm pretty sure this was caused by the late firing of the cylinder burning through the gasket. But, me not so smart when it comes to diagnosing engine stuff.
As far as the power valve. What is that, where is it located, can it be fixed, and how hard is it to fix? I'm pretty much a layman here, so bear with me.
Thanks,
Zac
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Joined: Aug 2000
Posts: 407
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Zac,
A good rebuild kit should have the proper replacement power valve. Is round –about the size of a quarter and is located in the primary (front) metering block. The valve provides additional fuel when the motor is under load. It opens when there is low engine vacuum as when the motor is under load. Once the load has been reduced, such as the vehicle getting up to speed and the vacuum increases again, the valve then closes.
Trucks generally have two stage valves because the load capabilities are so wide. One stage for when the truck is empty and the other for when it is carrying a load. Therefore, a power valve for a car would not be appropriate for use with a truck.
A design defect on the Holley carbs allows the pressure from a backfire to blow out the valve. New Holleys have a blow out check valve and older Holleys can be retrofitted.
The exhaust manifold gasket can be blown. Ford motors are notorious for the exhaust manifold studs to break and the manifold warping.
Good luck,
Mark
A good rebuild kit should have the proper replacement power valve. Is round –about the size of a quarter and is located in the primary (front) metering block. The valve provides additional fuel when the motor is under load. It opens when there is low engine vacuum as when the motor is under load. Once the load has been reduced, such as the vehicle getting up to speed and the vacuum increases again, the valve then closes.
Trucks generally have two stage valves because the load capabilities are so wide. One stage for when the truck is empty and the other for when it is carrying a load. Therefore, a power valve for a car would not be appropriate for use with a truck.
A design defect on the Holley carbs allows the pressure from a backfire to blow out the valve. New Holleys have a blow out check valve and older Holleys can be retrofitted.
The exhaust manifold gasket can be blown. Ford motors are notorious for the exhaust manifold studs to break and the manifold warping.
Good luck,
Mark
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From: TIJUANA/SANDIEGO
The 4180 has 4 scews that are caped or covered with metal.
Remove the carb from the car
You will need to drill the 4 small caps off. then a small allen wrench or better yet a Carb adjustung screw driver cable ( Its a screw drivier like handel hooked to a flex cable and has allen wrench attachements to it ) Sears / Pepboys or Harbor Freight has them)
At harbor freight tools they sell a O-Ring kit for about $9 If you ever work on a carb get one as many of the Carb kits dont come with orings for the needle valves.
To adjust your carb after you have the cabs opened.
1. Use your wrench and close ( But not with force, just untill it stops) the needle valves. 2. Open them 2 full turns- Each one .
Then start the motor. Have a Vacum line hoocked up with motor at 600 to 700 RPMs. Close each one untill you see a beginnig of a drop in vacum. Then open it back 1/4 to 1/2 turn. Do the same for all 4 screws.
Thats is as close as you can get to prefect.
Remove the carb from the car
You will need to drill the 4 small caps off. then a small allen wrench or better yet a Carb adjustung screw driver cable ( Its a screw drivier like handel hooked to a flex cable and has allen wrench attachements to it ) Sears / Pepboys or Harbor Freight has them)
At harbor freight tools they sell a O-Ring kit for about $9 If you ever work on a carb get one as many of the Carb kits dont come with orings for the needle valves.
To adjust your carb after you have the cabs opened.
1. Use your wrench and close ( But not with force, just untill it stops) the needle valves. 2. Open them 2 full turns- Each one .
Then start the motor. Have a Vacum line hoocked up with motor at 600 to 700 RPMs. Close each one untill you see a beginnig of a drop in vacum. Then open it back 1/4 to 1/2 turn. Do the same for all 4 screws.
Thats is as close as you can get to prefect.
