Hey folks,
I'm looking for some direction on the engine tune up procedure. I have a 67 F250 4x4 with the 352 engine. The engine is reliable and runs well, but I feel like I should be able to squeeze a little more out of it.
I have owned the truck for about a year and am going through the systems one at a time.
I've seen here in the forum several times that the carburetor is the last thing that gets touched in the tune up process.
I've also looked in the service manual and couldn't find a "tune up" procedure. From my research, here and on line, it looks like the following would be a good procedure:
Replace spark plugs, replace points/condenser in distributor, adjust timing with a timing light, after all that is good, then adjust the carb
Anything that I'm missing?
Appreciate the help. If anyone can direct me to where that is in the factory manual, I'll follow that procedure.
Thanks
Jeff

 

A careful rebuild of the carburetor pays off, paying particular attention to the throttle butterfly shaft for sloppiness and vacuum leaks. Your timing light for setting ignition timing is good, but also use a vacuum gauge for fine-tuning. Check for vacuum leaks and the PCV system for correct operation. Check the compression in each cylinder so you know what you can reasonably expect in performance. If you're looking for loads of power, a 390/410/428 built for torque at lower RPM might give you what you're looking for. Also, if you're looking for speed, the 4.56:1 differential ratios aren't going to give it to you! 4-8 MPG was common in the F250 4WD when they were new, which is why so many folks put auxiliary tanks on.

Good luck and post pics for us as you make progress!

 

If you don't have a Vacuum gauge get one , they are inexpensive and IMHO A must have for tuning old engines .

 

Don't forget about the spark plug wires. Old wires can have cracks.

 

Great stuff, guys
Thanks for the suggestions
Jeff

 

In the older manuals I think it was in "General Engine", I'd have to look, mostly dealing with compression specs and vacuum gauge reading. Ignition section has quite a bit, and then each section might have some troubleshooting.

I like the older MoToRs Repair and Chilton's for basic Tune-Up in one place. You can tune the carburetor a little bit as you go anytime, but every time some major operating point has changed (Ignition Timing) it doesn't hurt to make a pass through of the idle mixture. As the seasons change too idle mixture could be adjusted, and there is an accelerator pump rod on Autolite/Motorcraft carbs that are adjusted for the season as well.

Or let's say the fuel pump is replaced. It would be wise to take a static fuel pump pressure output test with your vacuum gauge to see that it is in spec, 4 to 5 psi say, and adjust/check the "wet height" to spec in the carb bowl. Then, adjust idle mixture again. It's easy to foul spark plugs with carburetors if they aren't setup right.

Be careful buying Ignition tune-up parts, things like distributor caps, rotors, points, condenser, they look the same but the cheap stuff is no good. There is nothing better than Motorcraft or Autolite when it comes to ignition components, or maybe NOS replacements like Standard Auto parts. Lots of crappy solenoids out there, battery cables, even spark plugs are junk now.

 

Hey Tedster. Really appreciate the suggestions. Rep sent.
Thanks for sharing.

 

Mikes 68 F100 is right about the mechanic's vacuum gauge. They really are the best bang for the buck in terms of utility. If you live at sea level for example, a stock engine in good condition and good tune will pull 18" to 20" steady needle at idle. If it doesn't, then there is a defect or defects somewhere, and need to find out why, because it won't run right no matter what you do. Sticky valves, exhaust restriction, leaky valve guides, weak valve springs, valve timing, compression, ignition timing etc, there are quite a few other faults and conditions that can be found if the user knows how to interpret the results.

One reason to utilize a vacuum gauge as part of a tune-up is because of how a carburetor works, they are calibrated to atomise an air fuel mixture through a restriction or venturi and then on to the cylinders right?The ignition timing advance and/or the valve timing, affects the amount of engine manifold vacuum directly. More advance = higher manifold vacuum, not just at idle but also throughout the RPM range.

Very little air actually flows through a carburetor at idle or just off idle where a lot of driving is done. So, the carburetor was designed to work around this problem by utilizing a special separate idle circuit that is open to the manifold and incorporates this engine vacuum for a strong signal or source of velocity to efficiently mix the air and fuel together at low RPM.

Now while it's called the "idle circuit", it's important for smooth acceleration just off idle up to around 35 mph or so together with the transition circuit. At higher speeds and RPM the carb is still calibrated around a certain expected air flow/velocity. What I'm getting at, is if the ignition timing isn't set to specification the carburetor won't work correctly anywhere along its operating range and it won't respond to adjustments the way it should. The power valve (economiser) for example would open and close at a different operating point than designed. The metering jets might not flow the same. Getting a sharp tune means making sure ignition and timing are correct.

Now someone might say "I have a timing light, what's the problem", one thing a vacuum gauge does is serves as a check or kind of QC on this and other adjustments. When the initial base ignition timing is set to spec, the engine vacuum should correspond to this. If it doesn't then that is a clue to investigate further. Sometimes balancers have the timing marks placed inaccurately, or the pointer is in the wrong place. Another common problem is the outer steel ring has slipped. So it's a good idea to verify TDC with a piston stop tool because all ignition timing events are based off this. If TDC on the balancer is wrong, everything that follows will be wrong as well.

A cylinder compression test let's you know right away the internal health of the motor. If compression is very low and/or uneven, then it probably isn't worth trying to tune it up. A big part of a thorough tune-up is just making sure things are within factory spec like, voltages, ohms resistance, fuel pressure, vacuum, temperature, psi. etc. The vacuum gauge will also help peak up the idle mixture, and every one I've ever seen also measures static fuel pump pressure output.

 

Ted tells it clear. Also be careful about changing out condensers. Most of the old ones are fine. A lot of Chinese crap out there. Find the Motorcraft stuff if you must change the condenser.

 

Thanks Ted and Brian, very helpful.
Tedster, your explanation was quite valuable. This is my first carb engine, so I'm learning the ropes. That helped a bunch.
Tried to rep you again, but it wouldn't let me.
I'll get you at a later date. Thanks for sharing.
Jeff

 

I would invest in a pertronix to replace the points and condenser....its really night and day for how well these old engines fire up and run with one installed...no one will know you did install one unless you show them under the distributor cap....no more dealing with setting dwell or gap etc....in an emp attack you can always throw your points and condenser back in the distributor....that would be the only reason I would ever run points and condenser again...lol....https://www.summitracing.com/parts/pnx-1281/reviews/

 

An overlooked part of a tune-up is ground straps or cables to the frame and block, firewall, and battery cables to starter, to relay, etc. Make sure first they aren't loose or even missing, they are important. They corrode internally and at the crimp, and were a bit undersized as gauge goes even when new from the factory. Copper is more expensive than steel, and the OEM kind of cheaped out when it came to cables.

If the cables are original or even just old they need to go bye-bye. Good solid clean tight shiny bright ground connections are important for starting, charging, ignition, lights, and accessories. Every single electrical connection, ground, bullet connector, multi-pin block connector through firewall, etc is a potential source of failure, they WILL fail, it's just a matter of "when". Oftentimes just cracking them open is enough to help. Dissimilar metal contact, air pollution, road spray and salt, it will ccorrode and eventually, fail altogether. A brass bristle brush and some kerosene or WD40 works good to clean them up. 12 volts is not a lot to begin with, and there are very high current demands in automotive circuits. I think the starter draws 100 or 150 amps, so ensuring clean, low resistance electrical connections pays for itself.

Even an almost invisible paper thin layer of corrosion at a connection is enough to cause problems. Another overlooked tool is an external battery charger of 2/6 amps, a good item to have on hand to keep the battery healthy and plussed up to 100%, it will pay for itself too by extending battery service life. Good batteries have become damnably expensive.

A good tune-up saves wear and tear on the starting system too. A poorly tuned engine costs money in more ways than one, grinding on the starter for more than just a few seconds at any one time will roast it, along with the starter relay. Modern fuel injection and electronic ignition have made jumper cables almost obsolete. Back in the day, it was a wintertime morning ritual in cold climates to see just whose car wasn't going to start, neglecting tune-ups and preventive maintenance would always catch up to certain guys.

 

Where do you buy Motorcraft parts at? The Ford dealer here in town says to get it online because their books don't go back that far (1967).

 

That famous auction site. Type in "NOS Autolite" or "NOS Ford" etc.. Now sometimes dealers may have old inventory on hand, but either way you'll have to have a valid part # to be sure a part will work.