How would I go about desmogging this old 300 in my 86 F150? I ask because the PO has done a terrible job at starting to desmog.

 

Your best bet is to completely revert back to a DuraSpark II ignition. You'll need the wiring harness from a DSII truck (or make your own), and then you'll need the distributor, ignition module, and a non-computer controlled carburetor (which the '86 came with stock).

Do a search for "DuraSpark II swap" and you should come up with plenty of info.


From there, you'll just need to remove all the multitude of vacuum lines, hoses, and wires that have to do with the ignition and carburetor, the big "brick" of wires going through the firewall, and the computer inside. You can remove the solenoids on the valve cover too. Buy fittings that plug the EGR and AIR setup and you should be good to go.

But, at least leave/put a cat in the exhaust. They're there for more than just passing a smog test.

 

This is not correct!!! If you make these changes you will end up with an engine that gets poor mileage less power and torque, burns valves and pings at partial throttle and wants to run on after you cut the key off. The easiest and cheepest would be to restore the smog equipment.
Without the EGR the carb needs to be one from the early 70s then rejetted for Ethanol (larger jets). If you go with Duraspark II or any modern Distributor it will need the internal advance plate welded and reslotted for the correct gap along with slightly stronger springs. If you don't do these two things you will have dismal MPG, hard starting and more.

 

Or just recurve the distributor ^

 

Then again..I never had a computer controlled truck..so I'm not sure if it applies to me...plus I did a whole lot more modifying to my engine

 

Wrong. It's completely correct based on the situation. Remember, the previous owner of the OP's truck has already ripped off all of the old feedback equipment, so the computer has locked the fuel mixture and timing. Provided he doesn't have emissions inspections in his area for his truck, he can safely revert to the DSII without any problem.

Pinging, run on, and burned up valves are usually the results of incorrect ignition timing and lean fuel mixtures. He can run ANY 1bbl carburetor that isn't computer controlled if it fits on his intake. Poor fuel mileage and low power can also be a lot of things, but a DSII swap isn't one of them.

He can get a Carter YFA 1bbl that's non-feedback, put it on his intake, tune the fuel mixture with a vacuum gauge, swap to DSII with a vacuum advance distributor, time it at 10* BTDC and he can do whatever he wants with that truck afterwards. And it's all a plug and play swap!

In fact, once he does it, I'd be willing to bet the title to my 83 F150 on the fact that his truck will not only run better this way, but run just as good or better than the stock TFI ignition system. This is, of course, provided that the swap is done correctly and that the motor is looked over and there are no loose ends left that could cause a problem with how the motor runs (vacuum leaks, bad gaskets, loose bolts, etc.)

Regarding recurving the ignition timing and manipulating the springs and weights inside the distributor, the general rule of thumb here is to tune it to run the most mechanical advance that you can without pinging. That will net the best mpg and power that your vehicle can produce. You also want to run the most initial timing that you can run without hard starts. This produces a higher vacuum signal, better fuel atomization, better gas mileage, more torque and horsepower, and better throttle response. However, it can be a hassle to tune the mechanical advance with a DSII distributor, and it's recommended to go with an aftermarket distributor so that you can tune the advance easier. To end this point, a DSII distributor, out of the box, will have an advance curve that is satisfactory and will not cause any issues with how the motor runs. Can there be improvements made? Yes. Can you run more advance? More than likely. Can you make your advance come in sooner? If you want.

Also, going with stronger springs inside the distributor will cause your advance to come in later, which is BAD for gas mileage and power. You want to run the most advance it'll handle, and you want smooth advance off idle up to the point where you want the mechanical advance all in. Depending on how the motor is set up, this can be anywhere from around 2000 RPM or higher. For a stock 300, 2000 RPM is a good point for the advance to be all in.

However, if he wanted to STAY with the feedback carburetor or he had no choice, then yes it would be better to replace all of the emissions equipment. But you also have to realize that some of the components to a TFI system are very hard to find 20+ years after the last one rolled off the assembly line. This is why some states have paperwork regarding inspections that allows them to wave off some missing components. These components that qualify are either discontinued or can't be found.

No disrespect or hard feelings meant, but there is no downside whatsoever to a DSII swap.

 

Thanks 83F150, I was going to reply with a lot of the same things.

This is a common swap, and the feedback setup is commonly known as problematic at this age. Going to a DSII is almost standard procedure.

And yes, since the feedback setup was made for only around 3 - 4 years, the parts are HARD to find.

If (BIG IF) it had been maintained, it's a great setup, and should be kept as is. That's just rarely the case. And going back and trying to get it back up to running order can be near impossible without someone who's pulled it all in working order off their truck.

 

Thanks for all the help and info y'all have provided me with. Hopefully I am right and my state doesn't require the smog stuff to be intact as its just all torn up.

 

A Carter YFA cannot be jetted to compensate for a removed EGR.
YFA air bleeds are enormous.
You can take the jets completely out. and the mixture will still be too lean and eventually damage the engine.Been their, done it, it don't work.
If you use a Carter, the YF is the only option that will work.
Not all carbs will work. Sounds good in theory but it don't work on the street.
DSII does not have the right curve for non-EGR, although it can be modified.It will work stock but it will ping at partial throttle with a load in high gear.

 

many of us here have went 100% desmog with no issues, state laws do come into effect but not really an issue from what i have read here with 3 way cats and the such.. DS11 dizzy on a non feedback card and setup for a 300 will work wonders and alot of great help here on how to do it.... shops will recurve ya dizzy for you if need be, myself i went the lazy way with a DUI setup

 

300s have low compression and a very conservative timing curve from the factory. They're made to tow. If anything the vacuum advance may need to be adjusted. MIne drove fine with late '70's vintage YF until I swapped on a 4bbl. I wouldn't sweat it unless you notice pinging at cruise.

And for all its negatives ethanol has a higher octane rating than gas, so there's that.

 

Explain to me why mine doesn't do any such thing, then. My truck is a 300 with Duraspark II, stock motor, Carter YFA carburetor. All of my emissions equipment is gone. I've had the bed squatting and loaded down with an entire elm tree, hauled firewood with it around the property more than half a dozen times, it has snatched a 10x12 building off of the block it was sitting on and drug it 200 feet with an 800 lb load in the bed and the truck squatting, and it then proceeded to drive down the road at highway speeds for over 30 miles with that same 800 lb load in the bed, although it did want to wander a bit due to the uneven weight distribution. It has also assisted in pulling trees while they were being cut to prevent them from falling on a well house. And, it has hauled around a dozen loads of brush. All of this within the past 4 months.

Did I mention it pulled that building across the ground in 2nd gear 4 low? It wasn't even in 1st gear. Wouldn't do it in 1st gear 4 lo because it didn't have enough wheel speed due to the low ratio of the NP435.

I can lean the mixture out enough to kill the motor, or I can enrich the mixture to where the motor is starting to shake at idle. How can I not adjust the fuel mixture to remove a lean condition with the YFA?

 

It's not the idle mix thats the problem its the running mix. This is controled by several things on a Carter. The main ones are the main jets, metering rods and the air bleeds.
Have you ever checked to see what your running mixture ratio is going down the Highway? You do this by running an o2 senser in the exhaust and recording the voltage output at different speeds and loads.
In my testing, a YFA is too lean no matter what you do to it and I didnt test just one, I tested several YFAs from different years. I put the largest jets made, no go. Then I started making my own jets with larger holes and support to center the metering rod, it was a no go, close but still to lean.
I am glad your engine runs perfect. There are always exceptions to every rule. Maybe you have a YFA that is a model I did not test.

I am not here to start trouble. I have just spent hundreds of hours and a lot of money trying to figure this out. I have also done the same testing on Toyoto truck 22r engines with emissions removed. I ran into identical problems.
I readily admit you can pull the emissions equipment and it will run pretty good but you risk excessive combustion temps (read this as short valve life, cylinder scoring, head gasket leaks and more)
I am just trying to let folks know what I found in my testing.
By the way an engine can be pinging and have excessive combustion temps and not be heard in the cab and the temp gauge will show the engine has normal coolant temperature.
Just my two cents.

 

There have been many postings here on removing smog equipment...and much of it is by those that have acquired trucks where the equipment has been removed, plugged, etc., and this is somehow thought of as being a profound bit of re-engineering. It is profound...but not as a compliment. To be re-engineered, all the systems have to go back to pre-smog equipment and tuning. It's more than just removing stuff and plugging vacuum lines.

 

But can't you compensate? To at least get the right conditions?