OK, I'm being lazy...

I want to work on switching out the old rubber fuel lines on my '86 f-250 6.9 tonight, but have no idea what size fuel lines to pick up on the way home. The return lines appear to be 1/4 and the one leading from the tank(s) 3/8 or 5/8.

Any ideas?

 

E3TZ-9324-AA Comes In A 10ft Roll 3/16 this is the fuel lines for the injectors.

 

Exactly which fuel lines............if you mean the injector return lines get the complete kit, due to the fact the plastic caps distort and will not always seal.

Here is how to....
First disconnect injector cap nuts, "do not bend lines" but move them away enough to get the return line caps off as a complete set per side.
After removal of the complete return cap and lines sets, build new sets identical. To remove old orings use a dental or oring pick with a razor knife, do not mark the injector body. When installing orings use lots of grease and roll first one into top groove, then roll second over that to bottom groove. When installing the new lines and caps use grease inside the cap and on orings, place them on respective injectors and gently push straight down until it pops into place on the orings. Install the line capnuts 22ftlbs torque. There should be a small space between the return cap and line capnut when finished, any major leaks mean caps are not seated or orings are cut or line cap nut is not tight. I have done two sets lately and found bleeding 1-2 injectors at a time on opposite side the best. Tighten lines then place fuel pedal to floor and fast idle and timing advance on, crank for 15 seconds max, mine started after 4th injector was on line.
Note when cranking engine and bleeding there will only be a slight amount of fuel/bubbles seen, no major squirting gysers, that only happens with engine running at idle RPM.

 

I replaced the injector return lines this weekend - What a difference! Before dropping $70 for the rail kit (that's what the FLAPS wanted), I decided to take it apart, inspect, then decide if it was worth it.

The lines were definitely past their prime - cracking everywhere. I initially purchased 3 feet of 3/8 fuel line and later had to get another foot. The tough part was getting the o-rings. Not because they were hard to find, it's just everyone was out of stock. I wound up getting them from a Lowe's about 30 minutes south of here. They're #9 o-rings, just for reference.

Other than that, I did a lot of cleaning and inspecting. I cleaned the heck out of the injector 'collars', then lubricated the o-rings with ATF before slipping the collars back on. I pushed down firmly, but not forcefully, twisting the colar as I went. There was a noticeable click when the collars were in place.

To prime the lines, I just threaded the lines back onto the ends of the injectors, leaving them slightly loose. Within 4 -5 good cranks, I had fuel bubbling out the top of the cap nuts on top of the injectors. In between cranks, I would check to see which had fuel bubbling out and tightened them down.

When it finally started, it chugged a little and smoked quite a bit. I'm assuming that this is because it was purging the remaining air and because I had replaced the fuel filter and filled it with ATF.

The change in the truck is like night and day. Now it accellerates like crazy. On the slight grade just up the road from the house that I was always loosing speed on, it now accellerates and I can get up to 65 before I crest the hill.

I appreciate the input and the other threads that I found related to this issue.