I have pulled up several older threads on this subject, but I still have a couple of questions. First off I do not have a timing light, but I do have a vacuum gauge from Harbor Freight. I read on this forum that a vacuum gauge is a must. So now to the two questions: Full disclosure I know nothing about this subject but I must learn.

1.) Using only the vacuum gauge I am getting 15 to 16 degrees (or inches of mercury, are these terms interchangeable?) vacuum at idle with the engine warmed up. Should I now turn the distributor to get 17 to 18 degrees?? I have read that I should be shooting for 17 to 22 degrees.
or
2.) Should I use the two carb mixture screws to try and bring it to 17 to 18 degrees vacuum?

Which comes first moving the dist. or adj. the mixture screws?
I hope this is not too confusing.
rsh

 

My fingers would fall off tring to explain everything. Hope this helps.

Get one of these it comes with a how to manual. Ebay; https://www.ebay.com/itm/Vintage-SUN...MAAOSwNPZdHnDu

 

Can use a mechanic's vacuum gauge to get real close to a good base or initial timing setting, but there's a catch to this. And still need a timing light to verify the internal distributor mechanical advance mechanism, the springs and weights works correctly through the entire RPM range, this is important. Then too, a timing light is pretty much needed to check that the vacuum advance diaphragm is working as it should too, that's also important.

The vacuum gauge will find what a particular engine "likes" for an initial timing setting, but this isn't necessarily what Ford decided to use. Keep in mind the initial or base timing is only a small part of the big picture, the OEM mechanical timing curve is almost always "too slow and too much". So if you get the initial timing set optimal with your gauge, and have a stock Ford distributor, what you'll likely find is it's engine knock or ping city out on the highway. You might even find your engine likes say, close to 20° BTDC base timing, but engine starter kickback looms if the starting system, battery, and cables aren't up to snuff, especially in hot weather.

For troubleshooting and familiarization, first disconnect and plug the vacuum advance port. Forget about vacuum advance for a bit.

The vacuum gauge is always connected to a source of constant manifold vacuum. If your engine is stock, or close to stock, and you live around sea level, the gauge should show 18" to 20" at factory idle in a healthy engine in good tune. If it doesn't, you want to find out why. You can try advancing the distributor clockwise slowly if it's only reading 15" or 16", but it's important that the needle is steady. If the engine is really worn, 16" might be the best you can get. There are some tests with the vacuum gauge you can do that will give a good indication of cylinder compression, but here again a compression test or leakdown test is something you should have done already.

Set the carburetor idle mixture needles last. Or, go back and forth really. Engine vacuum changes the optimum idle mixture point slightly. Turn them in (clockwise) from a start point of 1.5 turns out, one at a time alternating about a 1/4 turn at a time. You might see a rise in vacuum along with an increase in the idle RPM. This is good. Turn the idle RPM screw back down to spec. Then turn the idle mixture screws in slowly a bit more. At a definite point the idle RPM will start to stumble as it leans out. Back both screws out just slightly from this point. You can kind of go back and forth between the distributor timing and idle screws for the highest possible steady vacuum reading. Though they are called idle mixture screws, this adjustment has a big effect on the just off idle acceleration where most city driving is done, up to around 40 mph. If they are set too rich the spark plugs will start to load up after a couple minutes idle time.

When the idle mixture is missdjusted the gauge needle might float or waver about 1". For the initial timing backing off the distributor about 1/2" of vacuum from the highest steady vacuum achieved makes for a smooth idle and should run good on pump gas, but again this may be too much initial timing depending how the distributor is setup inside. Unless you're willing to get inside the distributor and change this, there is a limit to how much timing you can add without engine knock. Take it for a test drive, still without the vacuum advance hooked up and see if it pings or knocks upon hard acceleration in high gear at around 20 mph, something like that. Can play around with the initial timing that way.

When you are satisfied with the mechanical ignition timing, then you can re-connect the vacuum advance, and take yet another short test drive. Now at this point you're looking for part throttle ping or rattle, or rattle at steady level ground highway cruise that might go away as soon as you accelerate, it's kind of the opposite as before. The remedy here is to take timing out of the vacuum advance, or maybe add some more, depending on what it's doing or not doing. The takeaway, is don't mess with the distributor advance to try and compensate for too much vacuum advance. The two systems are always tuned separately, and the vacuum advance last.

You still absolutely need a timing light, the vacuum gauge is a great tool, but there's no getting around the need for a timing light.

 

Thanks for taking the time to type out and explain. I will print this off and do my best to follow.

thanks
rsh