I was told by a long time mechanic that getting a carbureted straight 6 to idle smoothly was impossible. Is there some truth to this? My 83 runs well, really well, but the idle is a tad lumpy. I've done everything I could to tune this baby up. New Motorcraft plugs, wires, cap and rotor. New fuel filter and pump. New ignition module and coil. Rebuilt the carb and replaced the rusted out choke stove heat tube. Checked all vacuum hosing. Yet, the idle does not purr steady.

Your thoughts?

 

What you call smooth someone else will say is ruff.


It all has to do with where the carb is on that log of an intake.
The holes closer to the carb run rich and the others far away run lean.
Because of the rich/lean can make the motor run ruff.
Dave ----

 

Is it all original? Does it have the computer system?

Was just posting the other day I have been trying to find the source of a rough idle on my 2.9 EFI 86 ranger for the past 6 years. I tried somewhat to straighten it out when I first got it with the standard stuff, and then through the years have changed various things out for various reasons, never have gotten rid of it. The other day I finally figured it out, the oxygen sensor is bogus. It doesn't throw a code but it isn't right either, it runs so much better with it unplugged. I am finding out these things probably should be changed out like quality sparkplugs should, probably every 50,000 or so.

Does your six have the computer system with the carb and the oxygen sensor? Does your distributor have a vacuum line going to it?

 

My 82 idles smoothly. Four problems I found
1. Vacuum leaks
2. Bad accelerator pump diaphragm leaking gas while running
3. Coil - I put a new coil on it just because I didn't want to repaint the rusty on I had and it improved the idle quality.
4. initial timing set with a vacuum gauge

 

Explain "initial timing with a vacuum gauge" please..

 

I set the initial timing advance using a vacuum gauge.
Please search here for this procedure or google it. These folks will do a better job of explaining it than I can.

 

A mechanics vacuum gauge is a great tool for diagnostics and tuning. Cheap too.

 

Yup. All original. 27,500 kms. No computer system. Carter FYA non feedback. No oxygen sensor that I know about. Base model with no power assist. Distributor does have a vacuum line.

 

My I6 idles very smoothly. It's still feedback, with a rebuilt carb, new plugs, distributor cap, and wires. Runs like a champ for the most part. I plan on going Duraspark or HEI along with a bigger carb and intake in the summer though in hopes of improving the abysmal MPGs and power.

 

So where is the initial timing set? Are you using ported or manifold for the vacuum advance? If manifold what is timing at idle? What idle RPM? Compression test numbers?

 

Please consider offering the feedback related components to someone on the forum who is trying to maintain their feedback system [don't just throw them away].

 

Just be greatfull you have a carb, us efi bullnose owners go threw all kinds of problems an just as you think you have it all sorted out, the next darn day your idle is back to crap! I plan on a aluminum intake an a hei with a holly an a electric fuel pump asap!

 

Ported vacuum advance.
Idle at 750 rpm
compression test was 150 in all 6 cyl.

 

I never throw anything away haha! If I decide to sell them this is the first place they're going up.

 

And initial timing is set to what? If too advanced it can run a little rough, too low and it can be lopey. Idle mixture set for highest RPM/highest vacuum? For smoothest idle you may end up a hair richer than highest RPM/vacuum. Verify the mechanical advance is working smoothly and fully returning every time, that initial timing does not vary if you rev it and let it return to idle. Mechanical advance needs to be cleaned and lubricated periodically. Sometimes springs may be weak and not fully return.