need a little timing help

[oldiron]

Need a little direction on this one. I just got the new harmonic balancer installed (Thanks Wild Horses), so that I can finally accurately time this engine. At first, initial timing (set by ear) was at 26 but idled great.
I backed that off to 12 degrees. Idle is a little rough but I'm still dialing in.
Problem is this: 12 deg initial...12 deg mechanical at 2500...but I'm getting 16-18 deg from the vacuum advance which is ported. With that much vacuum advance, and more initital timing (that this engine really seems to like) it adds up to way more than is allowable and the engine starts to break up at higher rpm. Any ideas? Is there a way to adjust the vac adv downward? This is an '86 5.0ho roller engine long block. The dist is an off the shelf unit for an '85 gt.
Greg

 

[DirtDonk]

Look inside the vacuum nipple on the end of the can (or feel inside with an allen wrench) and see if there is an allen bolt that can be adjusted.
This should be a limiter that might effect a little of when it happens, but mostly how much advance is added from the vacuum can.

Most do have them, but not all.

Paul

 

[oldiron]

Counter clockwise to subtract?

 

[DirtDonk]

Sorry, I forget. Didn't use them often, but I thought it was clock-wise to reduce/subtract.

One way to find out though!

Paul

 

[oldiron]

I'll let you know in about 10 minutes. lolol;D

 

[oldiron]

It's counter to subtract. But even at full out it's still adding too much timing.
Greg

 

[jckkys]

I have no idea what you mean by setting initial timing by "ear". At idle any engine will turn at higher RPM with timing far more advanced than it could run with. To explain what contributes to ideal ignition timing for a particular engine takes too long. Read this article;https://www.fordmuscle.com/archives/2000/03/timing/index.php.

 

[oldiron]

Exactly what i was looking for!!!
Thanks.

 

[SHX669]

I think Ford says limit the vacuum advance to 10 degrees - if i remember correctly. With my MSD ready to run distributors I had to use an Accell vacuum canister to limit mine to 10 * . They're adjustable .
That Ford Muscle site has a writeup on how to set your advance curve and limit your total mechanical advance .
Initial + mechanical advance should add up to about 34 * . Vacuum advance is separate

 

[DirtDonk]

There might be something else going on here as well after re-reading your first comments.
If it's breaking up at high rpm, is it doing it under light throttle? Because if it's during acceleration then the vacuum advance is not doing much at all under that low-vacuum condition.
If you're cruising and it's doing it, that might be different. But under load, you may have another issue because 24-25 degrees is not too much for one of these engines. Normally they don't respond negatively (as far as I remember) until you get into the 40+ range.
If you have an issue at under 30 degrees advance, maybe it's more of a jetting thing.

You said it runs rough at idle and 12 degrees. A rough idle is not necessarily a function of advance except where the carburetor is mis-matched to the timing. Not the other way around. And 12° is usually right in the sweet spot.

So keep messing with the timing by all means, but don't overlook other possibilities.

Paul