I have an 86 f150 which is running lean. I've done the DSII conversion, and with it, replaced the carb (1973 carter yf, manual choke), distributor, ignition module, plugs and wires, fuel pump, fuel filter, fuel sending unit, and coil. I am just about at the end of my rope with this thing. I've set, and re-set, timing. Adjusted the carb more times than
i care to remember. Checked for vacuum leaks everywhere I could...I cant figure it out!

The truck starts and idles great. No surging or anything. It even revs fine in neutral. However, once in gear and driving it has no power (even less if I mash the pedal), and it pops and sputters ALOT when decelerating. I read about cat's getting clogged, but i don't have one. And in fact, my exhaust just rusted through and broke in half the other day, so now I just have a straight pipe, so that's not it.

Please, wise and all knowing gurus...HELP!

 

I'm not an I-6 guru.
Maybe David or someone who actually owns one has a better idea, but have you checked your cam timing gears?

You say you have replaced all the ignition/fuel components and this is still a problem.
I'm not sure how your distributor is curved but being a 300 I doubt there are too many different ones available.

Your symptoms (won't take load, popping, spitting) seem to fit sloppy cam timing.
How many miles on the engine?
Is this the original phenolic cam gear, or has a metal (aftermarket) timing set been installed?

 

How was the engine running before the DS conversion? What makes you think it is running lean? What about the EGR? Did you block it off? What did you do about the EGR adapter located between the carburetor and the intake manifold?


How did you set the timing? If with a timing light, the harmonic balancer might have shifted. Try using a vacuum gauge.

 

I vote this route. Loosen the dist bolt just enough till you can turn it. With the engine idling, turn the dist till the engine speed increases just a little bit. Then take it out and see if there is any improvement. If there is, start playing with it and see how it reacts. Now that you have changed it around you can't really go by the factory numbers, and I do know the v8 balancers do like to slip when they get old and throw the marks off.

 

If your plugs are running lean than rejetting might be the cure. Why do you think it's a lean issue, though?

 

I agree with the two Daves - how do you *know* it's running lean (what proof do you have? Exhaust sniffer? AFR meter?) and how do you know the timing is set to what you think it is?

 

https://www.motorcraftservice.com/pu...9/VT120017.HTM

try this.

 

My truck had the similar symptoms which were fixed partially with a carb rebuild, but it still backfired on deceleration. I unhooked the AIR pump and it's been purring like a kitten ever since, not one backfire

 

Wow, I need to adjust my notification settings. Didn't know I had all these responses!
ArdWrknTrk, I do not know if the cam timing is correct, nor do I know if the cam gear has been replaced. This truck is said to have been rebuilt and have about 50,000 on it (after rebuild). While I can't confirm this, there is nice cross hatching on cylinder walls, motor holds great vacuum, and prior to this conversion seemed to have much more power.


1986F150SIX, How's it going? You helped me a while back when I was originally doing the DSII conversion, and I ended up going with the same carb as you (73 f-350 carter from Rock?) I know its running lean because the plugs where covered in white ash. Did you have to re-jet? I blocked the EGR at the spacer with the old aluminum can trick. Short-term shot in the dark, but the EGR was stuck open anyway. I set the timing both ways, and neither has really netted a solution.


I do believe my harmonic balancer has slipped or was put on wrong, and in addition I do not have the timing tab!! Now having said that, I have found TDC manually (screwdriver in the hole) marked this on the balancer at the driver side cast marks, and set to 6 BTDC. Re-checked timing a week later and it was still dead on. Today I checked the mechanical advance and vacuum advance and both seem to working correctly.


Frankiln2, Now that I have a verified good mark for TDC, I'll re-time by vacuum and see where it ends up.


NOW, after all that, I decided to re-jet today...the cheap way. I took the main jet from my feedback carb and checked it against my new carb. They are both stamped 120. Tried it out...same condition. So I drilled it out with a 1/8 bit...knowing that this should make it run pig rich. Put it in today, (WITH the metering rod completely tightened= as high as it can go) and it runs marginally better. Still doesn't have a lot of power after 1/2 throttle, but par throttle is a little better...most likely due to the metering rod being all the way out. At this point I'm looking into a faulty distributor or ignition module (though i'm leaning towards the former.)


Roadrash, I see you're also in PA. I'll try the diagnostics you sent and see where i'm at.


DeereFrod300, where is the AIR pump located?


Thanks to all!

 

I forgot to add that before the choke linkage on my manual choked carter FELL OFF, I could partially choke and get it to run great, with MUCH improved power. This to me suggested a lean condition, but I have read of people experiencing similar conditions with a faulty distributor. I still partially choke to get it to run better, but without that linkage, (1986F150SIX you know the one), it only restricts the amount of air coming in and no longer adds fuel.

 

I have used a DVM to read the voltage output of the O2 sensor to see if it is running rich or lean.
This might help as you work to get the correct mixture.
Jim

 

1986F150SIX, How's it going? You helped me a while back when I was originally doing the DSII conversion, and I ended up going with the same carb as you (73 f-350 carter from Rock?) I know its running lean because the plugs where covered in white ash. Did you have to re-jet? I blocked the EGR at the spacer with the old aluminum can trick. Short-term shot in the dark, but the EGR was stuck open anyway. I set the timing both ways, and neither has really netted a solution.


I did not have to re-jet.


I do believe my harmonic balancer has slipped or was put on wrong, and in addition I do not have the timing tab!! Now having said that, I have found TDC manually (screwdriver in the hole) marked this on the balancer at the driver side cast marks, and set to 6 BTDC. Re-checked timing a week later and it was still dead on. Today I checked the mechanical advance and vacuum advance and both seem to working correctly.


My static timing is @ 14 degrees BTDC. Mine would be a d-o-g if set @ 6 degrees BTDC!!!

 

JimsRebel, I've heard of reading voltage from an O2 sensor for tuning the mixture, but am unsure of how to do it...I'll look into it.

86- Strange that we have very similar set-ups with very different results. If I ran 16 i'd be pinging the whole way. I'm guessing you re-curved your distributor if you're running that much initial. That's another thing i'm not sure how to do. Change one of the spring I believe...also will look into it. Thanks guys, this has been a real headache/wallet ache for some time now.

 

bg_,

Carry a 1/2" wrench with you in the truck. Loosen the distributor hold-down bolt and rotate the distributor clockwise slightly. Drive with warm engine and place under a load. If no pinging, stop and repeat the procedure. Once pinging is detected, stop and retard the timing [turn distributor counter clockwise] just enough to where the pinging stops, or is just very slight while under light load.

Once you get to that point, gently insert an 1/8" long shank allen wrench into the vacuum advance canister [remove the vacuum hose] canister and turn the adjustment about 2 full turns and then drive. Reattach the vacuum hose. Listen for pinging while under light load. This is adjusting the vacuum advance. Keep up with the number of turns so you can go back, if necessary. Once too much pinging is detected, turn the adjustment counter clockwise enough to lessen the pinging.

Most Duraspark vacuum canisters are adjustable. Mine was turned 6 1/2 turns from where it was as delivered. Gas mileage increased with each adjustment.

This light load pinging will go away once the vacuum drops while accelerating.


Of course, one can advance the initial timing too far and the starter motor will drag. Each and every engine has its own set of characteristics, especially as "we" re-engineer them by making changes. The balancing act regarding timing is to find the "sweet spots" for three areas: initial timing + centrifugal timing advance as well as the vacuum advance!

 

Haha, I've been carrying that wrench up front so long it has it's own seat! But you're right, I guess I feel like this must be a timing issue portraying itself as a lean condition. But I keep thinking about how choking the engine made it run normal??? And the white plugs? A mystery...

Anyway, I decided to cash in on my distributors lifetime warranty and start fresh with a new one. I'll put it in today and report back....of course if the old distributor WAS the problem, I'll be running pig rich and crappy! HA