next steps, carb and tuning questions

[cjarvis]

Hello again from MI. I have a few more questions before taking the next steps on this truck.

The brief history is:

- 1971 F-250 360. Believed to have 26K original miles, having sat from 73 until May 2009
- Work done by PO May-August: new gas tank, sender, fuel pump, coolant hoses and coolant change, front/rear brakes, hoses, wheel cylinders, calipers rebuilt, spark plugs and wires, engine oil change, battery
- Work done by me since getting the truck in Sept: changed trans/torgue converter oil and filter, changed rear end oil, replaced right exhaust manifold gasket, replaced all lifters and push rods (seized lifters and 2 bent rods), engine oil change

As of now it runs pretty good, but there are a few issues like poor gas mileage and poor performance taking it off idle (especially cold). If you take it off idle too quickly, it will at least hesitate. Sometimes it will fall on its face, sometimes it will die, sometimes it will have a small pop through the intake. Its a lot worse when cold. Sounds to me like its running rich, but it doesn't smoke, and there inst any gas in the oil. When I set the timing after the lifter job, I couldn't read the numbers on the dampener so I went with the white mark on the dampener. Probably a good bet the mark is on the spec. Haven't checked dwell yet, but will.

So I am thinking carb adjustments might be next step, but I have a few questions.

- What do the 2 lines that come of the right exhaust manifold do? See pic: http://picasaweb.google.com/cjarvis99/S ... 1972877650. the one that goes to the choke has rotted in two. Are replacements available? Or do I have to fabricate one?

- How do you adjust the choke? Pic: http://picasaweb.google.com/cjarvis99/S ... 1491371666. After loosening the screws and rotate it while cold, but do you rotate it until the choke flap is just closed? mostly closed? Some other way?

- How do you adjust the jets? I seem to remember back when they were adjusted for best idle. But this carb has 2 adjustment screws. Do you go back and forth make small similar adjustments to each until the best idle? does anyone use a wideband O2 sensor and adjust based on AFR? overkill?

- My cold idle seems low, and I dont see a cold idle cam on the linkage. Is the device at the bottom of the pic here some type of thermal cold idle:
http://picasaweb.google.com/cjarvis99/S ... 0503117778

I really appreciate any advice, information.

Craig in MI

[TNIceWolf]

The way I see it every problem you mentioned could be caused by the condition of the lines in the first photo.Those are for a heat circulation system to the carb. It has a lot to do with smooth running and choke operation. Get a vacum leak and it wont idle or run right when you grab the throttle.........no heat to the choke.....it's gonna be even worse.

[rd100]

I just rebuilt my carb on my '71 302 and those carb choke heat lines weren't attached down at the manifold, they were just sort of hovering around the holes they fit into.

I took off the old tubes and got 1/4" brake line and bent it into a U shape and got hose to attach the ends to where the old setup went. I clamped the new U part onto the exhaust manifold near where the previous was.

When I took the old tubes apart, one end near the carb that had a bend in it was solid packed with some sort of carbon residue.

[cjarvis]

Update...
Truck is running great! Turns out the white mark on the balancer that I set the timing to was at TDC, not 6' BTDC. I reset timing to the 6' BTDC (Chilton says that is the spec) and all is now good. Dwell was at 31', adjusted to 28'. Replaced the choke stove pipe from the exhaust manifold with a kit from Napa. I haven't touched the carb yet, but it cant be far off with how well its running. Put tires and shocks on and had it on the highway doing 80. Zero vibration, even in the steering wheel. Oh Yea!

I am assuming there is a centrifugal advance in the stock distributor because I see most of the advance in timing whether the vacuum line is connected or not. I am not sure how much advance I am getting, but it seemed like about 20' based on how far my mark moved. I only see 5 in of vacuum on the hose that feeds the distributor at idle, and 15-17 in of vacuum at a port at the back of the intake. The hose to the distributor will get to 10-15 in of vacuum at higher RPMs. Air cleaner was off for all these checks. Does all this sound pretty typical?

Anyway, I am pretty thrilled with how its running. I'm not thinking there is a lot left in adjustments.

Thanks for all the info and advice. This is a great forum!

Craig in MI

[knightfire83]

If you want to wake up the old 360, set the timing between 12-14* and adjust the carb accordingly for a good idle. I'm running 14* on low octane fuel with no detonation, it really made a difference in power. Make sure to disconnect and plug the dist. hose when timing.

As far as the vacuum thing, there should be no vacuum at the distributor advance unit at idle. Sounds like the hose leading from the carb is on the wrong port or your idle screw is set to high opening the port just a bit.

Find a port on the carb. that only has vacuum when the throttle linkage is moved, and hook the dist. advance to that.

And yes, in addition to the vacuum advance the distributor has little weights & springs inside for cintrifical advance.