New Member! Need help!

[nilknarf007]

Hello everyone!  Rob here, got this beauty for a steal.  A tree fell on it and really damaged the bed, so the 92 year old original owner decided to sell it.  120k original miles, and previous owner says he rebuilt the engine at 110k.  Engine runs great, and doesn't use oil.  I put a wooden bed on it, and some new rims and tires.  But - there always is a but - this truck has a lack of power.  Even at highway speeds (2400 rpm) it will lose significant speed on anything more than the slightest grade, and that was before the bigger tires.  

I'm fairly mechanically competent, but carbs have always been a mystery to me.  On this YFA single barrel, I've checked for vacuum leaks, adjusted it as best I could, and even ran some Seafoam through it, and nothing has helped.  I know that if I try a carb rebuild it will be disaster (I know my limitations).  I've also checked the timing, and I think it's spot on.

All of the smog stuff has been taken off, and there are a ton of plugged vacuum lines.

I'm not really interested in upgrading the carb, such as going to a 2 or 4 barrel, but does anyone think that a newly rebuilt YFA will be an improvement?

[grumpin]

Welcome!

I usually check for vacuum leaks first.

[Sac79]

Welcome. I'm not an expert, barely competent in fact, but when I started tinkering with my truck, I was told I had two options, replace all the systems to original spec or delete the computer. From what I understand, the computer requires everything to be just right before giving you full power. So all the PO achieved by removing stuff is reducing power. To remove the EEC unit you can either replace the ignition with a Duraspark system or HEI distributor. I'm sure someone else will chime in with more details...

[Gary Lewis]

Yes, welcome!  Glad you joined.  

Where's home?  We have a member's map I'd be happy to put you if I had a city and state.

On the lack of power, Rob has a good point.  If you have a computer it will be controlling the timing.  But if the emissions stuff has been removed the computer will have its knickers in a twist and won't advance the timing and you won't have any power.

So put your timing light on and see if the timing changes as you rev the engine.  It should go up with R's, starting around 1500 to 2000 RPM.  If it doesn't then timing is locked by the computer and you'll either need to put everything back, or better yet put a DS-II ignition on it.  It'll make a huge difference.

[1986F150Six]

Welcome, Rob! How is the gas mileage?

David

[nilknarf007]

I get a solid 11 mpg no matter how I drive it.

[nilknarf007]

I'm in Marietta, GA, and glad to be a part of the forum.

I'm going to check the timing within the hour and report back.

About the ignition, I have electronic ignition already (no points).  Does that mean that the DS-11 is all I need to bypass the computer issues?

[1986F150Six]

Rob, I used to work in Marietta and lived in Powder Springs. Small world!

The carburetion and ignition system for the 4.9L engine was the same from 1984-1986. When I first bought my 1986, it returned 9-11 mpg, the first two tanks. The computer was not receiving its needed input due to faulty sensors and leaking vacuum lines. The engine ran poorly and bucked on deceleration.

If I remember correctly, you no longer have to pass emissions testing [greater than 25 years old]. Is that correct? If so, and you have a little time, you might gain some information from my quest to improve performance and fuel efficiency.

https://www.ford-trucks.com/forums/1325963-gas-mileage-recipe-4-9l-300-a.html

[Gary Lewis]

Rob - You are on the map.

As for the ignition, all Bullnose trucks had electronic ignition.  But some trucks had computer-controlled electronic ignition.  And if you did much to the system the computer put the timing into limp-home mode, meaning it locked the timing to the initial advance.

I once bought an '82 351W that set on a used car lot for years because someone did something that made the computer mad and the MPG and HP went away.  But by swapping out the computer-controlled system with a standalone DS-II ignition system it ran well.

David's thread, in his link, chronicles quite a saga of going from what you are getting now in MPG to over 20.  I'm pretty sure you can do the same, but before we get too far please post some pics of the distributor.  Just want to be sure of what you have.

[844rd]

Mine was the same way, flat. Had to accelerate slowly. If you pushed harder on the gas it would not go any faster and would loose speed on a hill. I replaced the 1 barrel Carter that had the "feedback" system with a rebuilt one with no feedback. Replaced the ignition system which was the EECIV computer controlled to the DurasparkII and now runs great. All the power I need and gas mileage 20-21 mpg.

[nilknarf007]

Wow!  Thanks for all the good info.  It seems the timing was at least part of the issue.  I put a timing light on it and saw NO MARKS.  I shut off the engine and searched for marks and found nothing I could be sure looked like a manufactured mark.

I did some reading and found a debate as to whether or not the notch was the factory mark.  The debate seemed to be 50/50 so I made a white mark on the notch and tried again.  Nothing.

I put the timing light on the #4 plug and bingo, I saw the mark at about 15 degrees AFTER TDC.  I advanced it to 14 degrees before TDC.  The idle went up from a rough 650 RPM to 1300 RPM.  Tried to adjust the idle speed but the adjustment screw didn't seem to do anything.

Anyway, I took it for a test drive and it ran like it had 50 more HP.  Came back and checked the advance, and discovered that the timing does not advance as you rev the motor.

Questions: Anyone have any feelings as to the notch and it's relationship to TDC?  I guess the lack of advance proves the computer is in limp mode?  Any ideas on why the idle adjustment has no effect?  I bottomed it out both directions and nothing.

[Gary Lewis]

You may have multiple problems.  But first, when you say "adjustment screw", you do mean the curb idle adjusting screw shown below.  Right?

If that has no effect then you have a significant air leak.  On the 300 six the carb attaching nuts have a tendency of loosening, so make sure it is tightened down, but don't break anything.  If that isn't it check all of the hoses and vacuum caps for cracks.  David will teach you how to do the smoke test to check for leaks if needed.  

I'll let someone else speak to the notch.

And yes the computer is in limp mode.  You will need to to replace the ignition system, but you may get by with the existing carb.

[nilknarf007]

Yes, that's the screw I'm adjusting.  I'll check the other things you mentioned.

[nilknarf007]

844rd You went from this carb



to this one?

[844rd]

The feedback one wires going to it for computer control. The one I put on came from O'Reillys Part#1-506 372.86 Rebuilt by TAMCO.

[ArdWrknTrk]

Welcome Rob!  

When you checked the timing did you remove the SPark OUT plug?

If not, you're not really checking base timing.
Much like if you were to check a conventional distributor without disconnecting or clamping the vacuum hose.

Not meaning to question your ability, just gathering clues.

[ArdWrknTrk]

That's a working truck!
I like it.  😎

Soft-8's fit, but you might consider small side reflectors with signal lamps.

I'd get busted around here for that, and it's always better if other drivers know where you are and what your intentions are.

[1986F150Six]

Gary Lewis wrote

If that has no effect then you have a significant air leak.  On the 300 six the carb attaching nuts have a tendency of loosening, so make sure it is tightened down, but don't break anything.  If that isn't it check all of the hoses and vacuum caps for cracks.  David will teach you how to do the smoke test to check for leaks if needed.  

Here you are: https://www.ford-trucks.com/forums/1478167-vacuum-leak-detection-effective-and-inexpensive.html

[nilknarf007]

Hadn't thought of that, but it makes sense.  I'll take care of that today.

[1986F150Six]

Note that under the carburetor on the passenger side is a "vacuum tree" which has about 6 or 7 ports. This is attached to the intake manifold. Not all ports are used and some are covered with a rubber cap. During the years, the heat and exposure to the atmosphere reeks havoc on the rubber and it hardens and cracks or falls off. I have found on my son's 1984 and my 1986 [both with 4.9L], that there is one particular cap which is hidden by the "spaghetti" of vacuum hoses on the passenger side. This particular port is nearest the intake manifold and nearest the exhaust manifold [heat source]. On mine, it had cracked; on my son's, it had a large opening in the center.

Be sure to look closely at that one.

By the way, that smoke test was on a 1984 with the feedback emissions system still in operation [original].