So I have a 1980 F-150, with the 300-6 engine. The carburetor on it was recently (~500 miles ago) rebuilt, but I have since learned that no adjustments were made to it once it was bolted back on the truck. The truck runs rich and suffers from a lack of power at speed, so I think it's time to get in there and see what can be done.

I've found lots of good advice for adjusting these carburetors, but they all assume you know which screw or other doodad is which - and I don't. So I found a website (Carter YF Manual - The Old Car Manual Project) that has a guide to these carburetors, but the most relevant one is for 1972 Fords. My question is this: are there any major differences between the carburetor on my truck and what's in the diagram that I need to be aware of? My carburetor certainly looks like what's in the pictures, but I'm sure *something* was changed in 8 years.

 

The carbs are relatively the same.

There is a fuel mixture screw on the passenger side of the carb, and the two idle adjustment screws are on the drivers side. (left hand drive)

To adjust the fuel mixture, make sure the idle screws are adjusted properly, Use the safety certification lable for idle speeds.

Turn the fuel mixture screw a couple of turns out, with the engine running, then turn the screw back in untill the engine starts to idle slower, then turn the screw back out one and a half to two turns. This will get you in the ballpark.

 

Thanks - that's the kind of advice I've found elsewhere, but without knowing which screw was which, it didn't do me any good.

Any words of wisdom on choke adjustments? My dad (who rebuilt the carburetor) suggested that maybe the choke wasn't opening up fully when warm.

 

The mixture screw on the pass side is just the idle mixture adjustment. It affects the mixture at idle and near idle operation. Changing the mixture at higher flow when you are mainly running on the main jet requires either a jet change or adjustment of the step rod, both of which are inside the fuel bowl.

 

Dorsai,

With the engine at operating temperature and turned off [for safety's sake], carefully remove the air filter assembly.Make a mental note of where everything goes [i.e. vacuum lines and hoses], so you can get it back together. Looking in the throat of the carburetor, there is a plate which should be fully open [meaning straight up], so the most air can enter the carburetor. This plate is attached to a shaft which allows the choke plate to pivot. The plate should be fully open when at operating temperature and almost completely closed when cold. The plate is opened by a bi-metalic spring attached to the end of the shaft with a black plastic or phenolic cap. The cap is held in place by a metal ring with 3 screws. On the metal housing where the cap is located will be marks with the words "lean" and "rich" on either side of the marks. Once the screws are loosened [not taken out], this black housing can be rotated. When rotated toward the "rich" end, the plate will close more and open later while the engine is warming. Likewise, when rotated toward "lean", the plate will open more and open more quickly.

Look at your choke plate... is it opened fully, while engine is still hot? If not, mark where you are starting from, so you can undo any adjustments later if you desire. Next, loosen the 3 screws and turn to where the plate just opens fully. You will need to repeat this procedure when the engine is cold, to see if the plate is closed, usually with a slight opening.

Make sure the wire providing electricity is attached to the one tab on the choke [black plastic housing]. If wired as original, this power comes directly off the alternator and is only "hot" when the engine is running.

Most likely, you also have a metal tube with an insulating covering attached to the choke housing. This gets hot air from the exhaust manifold area and facilitates the heating of the choke. Many times, this rusts off, but can be replaced. Without it, the choke takes longer to open up.

All of this is based on the assumption that you have a non-manual choke.

Hope this helps!

 

Dude...that is *exactly* what I was looking for. Thanks!

 

Not specific to the posters question but for completion sake, On the feedback equipped carter carbs, the mixture screw also controls base mixture. If it's not set right at idle it will effect the whole driving range of the engine. this only affects 1981 and later with feedback carbs.

 

Some of these choke housings are "NON Adjustable" from the factory and take a little modification to make them adjustable.

Look at the emissions control lable under the hood, under Choke settings, and it will either give you the specs for adjustment, or say NON-adjustable in the space provided.

So if you can't turn the housing, this may be the reason why.

 

Good to know, thanks. I plan to try this over the weekend, and I will report back on Monday.

 

On a feedback carb how is this set up?
On my feedback carb I could run the mixture screw in all the way... didnt seem to change anything so I just set it at 1 1/2 turns out or so.

This is good info, I will hook up the DVM to the O2 sensor again (when it gets warmer outside) and try to fine tune the mixture. I am currently a bit rich (.7 to .8 volts) at around 35 mph. Freeway driveing at 55-60 is when it goes lean.
Jim

 

This is most likely because the computer adjusted the fuel mixture and basicly fought with you on adjustment. This is why a propane enrichment proceedure is recommended in the Ford manual for feedback carbs.

However forgoing that, because the tools are most likely no longer avaliable at the dealer. Hooking up the truck to a smog check sniffer, can get good results if avaliable in your area. This is the closest you can get to fine tuning.

The lack of fuel mixture adjustment could also mean the carb is sucking air in, where it shouldn't be sucking as well.

With my feedback carb, I found I can adjust it like a regular carb, but the computer will try and fight you, so you shut it off and clear the computer and restart it several times untill the adjustments no longer changes. This is counting the turns of the screw in about 1 and 1/2 to two turns untill the engine starts to slow down, and backing it back out the same amount, and the adjustment does not change after two consecutive attempts.