Brand new here. . .haven't spun wrenches since my go-kart racing days, excited to get going on this project.

I just got a 1981 F150 4.9 300 I6, not running well. I replaced belts, battery, brake booster, cap & rotor, exhaust leak at donut, fuel filter, got someone to take the carter yf carb (elec. choke) and rebuild. We tried to fix the vacuum emissions system as it was TOTALLY wrong but not sure we got it completely right. Think it's missing a few things.

Engine has a hard time starting and idling, if I do get it started, seems to run well for a few min, then wants to die, then runs fine for a few min again.

Wants to keep running a bit when I turn it off.

I was thinking about taking off the smog crap, is that easy? Is that part of my problem? Plan to run a test on the fuel pump (not electric pump).

No emissions test for this vehicle in Austin. Not sure where to go from here, ideas?


". . .but outside a' that, she's cherry." - C.W. McCall

 

If there is no risk of a smog test go ahead and toss that smog junk.
It is not hard to do. The easiest way is to rip it all off and toss it in a garbage can then go buy a reman carb that will work without all that stuff. Some carbs need the smog stuff some dont. You have to decide that.
I think the 4.9 had only EGR and dashpot for emissions though..........

Have you simply tried timing it?

 

Thanks for a quick response!

I plan on checking the timing as soon as I get the timing light.

Can I just cap off the vacuum lines that I don't need coming from the engine?

Can I just cap off the inlets on the carb that I don't need?

 

Hey texascraig, welcome to the forums.

The '81 300 is pretty bare bones on emissions stuff. When I removed mine (had to since I changed the exhaust manifolds), there wasn't a lot to do. There's the AIR pump that shoots air into the exhaust manifold, and then the EGR valve below the carb. That's about it. Unlike later years, there's no air injection in the head or anything.

To remove, just put a block off plate (you'll probably have to make one, shouldn't be hard though) over the EGR port, or just make a gasket that covers the holes and leave the EGR in place (no vacuum hose) to hold it on. If you want to go all the way, you can remove the EGR pipe, but I don't think it's necessary.

Then, just unbolt the air pump and remove it. Go down to a hardware/plumbing store, and get a pipe end cap that has the same thread pattern and put it in the EGR spacer where the air hose comes in.

That'll do it.


After that, I'd recommend replacing ALL your vacuum lines with fresh new lines. Those plastic ones get brittle and start to leak through dozens of hairline cracks that you can't see.


Your carb will run a little lean because the EGR system richens it up a touch, so you can either put a slightly larger jet in it, or replace it with a pre-emissions carter 1bbl.

If you're want to run clean still (hope you do), put on a 3-way cat and you'll still be running cleaner than when your engine was new. With all the emissions stuff removed on mine, I still easily passed my local emissions.

 

I have never seen a working smog pump on any vehicle from 85-forward. I seen pictures but never a pump. I thought it was just a legend.

 

Okay, so I guess I will need to find a pulley to replace the air pump, can I find one for this vehicle that uses the same belt, or do I need to change the belt too? Thanks for the ideas on making this thing run better.

 

If yours is an '81, you should have a separate belt for each accessory. Just remove the air pump's belt with the air pump. It'll just leave an open belt slot on the main pulley.

 

an open belt slot

Can't have THAT, now can we? Need 2 put a sno plow pump or on-board-air on other nice accessory on ;-)

 

Hrm...that's an interesting idea. What size of belts do those use though? The air pump belt is, if I remember right, only about 1/8" - 1/4" thick.

An on board air could fit right where the air pump was.

 

Thanks y'all!! I got all the smog stuff off of it and pluged everything up, homemade gasket and all. The truck runs great! Never idled or ran better.

Only thing is, it's hard to start; fires right up when I put gas in the carb. . .hmm. I probably need to mess with the electric choke, but not sure where to start.

I am supposed to get my dad's timing light in the mail today so I will check the timing this weekend, could that be part of the problem with the hard starts too?

I can post this as a new thread if anyone thinks I should.

Thanks again.

 

Hard starts *can* be a symptom of too much timing advance. However, if putting gas into the carb helps it to start better, than probably not.

To check the choke, when the engine is ice cold, push and release the gas pedal, and then pull the air cleaner off and look at the butterfly valve on the top. It should be almost fully closed. If it's more than 1/16" - 1/8" open, it's too much and you need to back it down a little bit. If it's completely closed, you'll have a really hard time starting it, if it starts at all.
After it's fully warmed up, look at it again, it should be completely open. If not, loosen the three choke screws and rotate it until it's just barely enough to keep it 100% open. If you go too far, it'll still be completely open, but won't close down all the way when the engine cools off again.

Lastly, when I got my Bronco, it had the same problem where it would only fire right up when I poured gas into the carb. Other than that, it was a real pain. It was a dying/half dead fuel pump.



Removing all of the emissions equipment can make it run a bit lean, since the EGR richens the mixture up a touch. You may want to look into getting a slightly larger jet in the carb. It helped a lot with mine. Mine would also bog off of acceleration before that, which is another symptom of running lean.

 

Is the choke supposed to flap open and shut when I'm starting it?

 

No, it is not.

 

Didnt think so. Gonna take apart the choke, maybe it's a bad spring or it's put together wrong. Thanks!

so close

 

I took it all apart and it all looks good to me, I have no idea why that choke flap is moving when I'm trying to start it.