Dustin_429

I can't get the timing set right and it's getting really frustrated . Please help me if I'm doing something wrong . timin the vacuum advanced off , plug it . Hook up timing light , have idle set at 900rpms . And when I move the distributor to adjust the timing the rpms slow or speed up and moves the timing and have to re set it and it never lands where I want it . Should the timing retard itself as the rpms get higher , ( or rev the engine ) with the vacuum advanced off ??

zraffz

Just to clarify, you cap the end of the vacuum advance at the vacuum source and not at the distributor.

Yes, as you turn the distributor the idle will raise or lower a little bit. The timing will advance/increase as you rev it up.


The way I like to set timing is to put the lightest springs and weights in the distributor that I have. I bring the RPMs up to about 3800 and set my timing all in at anywhere from 34-37 degrees. Then I rev it up a little higher to make sure the timing isn't still increasing past 34-37 degrees.

This lets my base/idle timing drop wherever it wants to. Too many people get hung up on running "XX" timing at idle but that won't help or hurt your performance as long as the timing is all in nice and early.

AlkyIROC

Base timing really depends on the cam grind. For a stock cam, 6-8* is normal but can also be bumped up to around 12* but if the base timing is too high, the engine can be hard to start because the plugs are being fired too soon at such a low RPM.

As mentioned above, total timing is very important to make max power. Where an engine likes it's total timing depends on each engine. Once the best timing is determined, you never change it. Anything else you do to improve performance through tuning, jets etc, won't change where the engine wants the timing.

What camshaft is in the engine? How many degrees @ 0.050" lift?

sofakingdom

iTrader: (1)

Put down the light and forget about cap the vacuum and all that.

Then, give the engine the timing IT wants, not make up some random number in your head that YOU want. Odds are, they won't be ANYWHERE NEAR the same. ASK it what it wants, not TELL IT what YOU want.

Of course, make sure your distributor is working right, and has an appropriate centrifugal (RPM) curve in it. "327" is not a factor. The fuel you run, the compression, and the cam (insofar as it affects actual cyl pressure at low speeds), are what matters.

Since you run gasoline, the engine will run best with about 36° of advance at full power and at the max torque RPM which should be somewhere in the 3000ish range for a typical street motor. It will probably run best with springs, weights, and weight cam in the dist, that give a low-RPM retard (aka "centrifugal advance") of around 15 - 18°, with the retard starting at around 2800 RPM and reaching full retard just off idle, below your converter stall, maybe 1200 or so. Then you'll want about 15° of vac adv on top of all that; the engine will probably appreciate it hooked up to full-time manifold vacuum rather than "ported".

It REALLY helps to think of timing that way, i.e. as the thing you are trying to hit, is that magic 36° full-power high-RPM number, whatever it is exactly for YOUR engine combo. 99.999% of the time it will be between 34 and 38°, that being determined by how fast gasoline burns. Then as the RPMs decrease, your curve should back it off so that combustion continues to occur at the optimum time, which is, just reaching completion at or shortly after TDC. Obviously at low RPMs the burning process takes up less of the time of upward piston motion, which is why you typically want less advance at low RPMs.

Unfortunately that's not how a mechanical distributor actually works, which is why even though that's how THE ENGINE works, you have to set the dist up backwards to that; that is, start with "static" advance at idle, then add "centrifugal advance" as RPMs climb, reaching "total" advance at some point. But if you look at the description I just gave of the "ideal" curve, it means that you'll want around 18° of "static" advance, a total of about 18° of added "centrifugal" advance as the RPMs increase, starting at around 1200 RPM and reaching a "total" of around 36° at about 3000 RPM or maybe a little earlier. Then of course when the engine is under very light load at high speeds (aka "cruising") you want the addl 15° or so of "vacuum" (load-based) advance, to start the combustion process earlier when burning is very slow due to less cyl fill at cruise (throttle blades mostly closed, blocking the intake) and the leaner mixture at those times as well, all of which make combustion last that much longer, but you still want it reaching completion at or slightly after TDC.

All of these numbers assuming of course, that your timing marks are ACCURATE, which I would bet MONEY they're not, not in your engine any more than they are on anybody else's. The "mark" is on the OUTSIDE of the crank damper, on the inertia ring, which isn't even CONNECTED to the crankshaft. It's merely LOOSELY ASSOCIATED with the crank by way of a blob of spooge which is subject to all manner of failure. Yet another reason to put down "light", don't waste your time on "mark" and "tab", and forget about "number" and "spec" and "book", and just give the engine what it wants.

Give THE ENGINE what IT wants.

Remember, if I may paraphrase the wisdom of one of The Greatest Ones Ever in a completely unrelated field,

"If it RUNS good, it IS good".

So simple. Don't outsmart yourself unnecessarily.

paulo57509

Just to be clear on your description of what's happening....

You twist the distributor to where you want it by looking at the mark on the crankshaft balancer and the timing tab. It's all lined up and you tighten down the hold down clamp and when you go to re-check the timing mark the mark has moved.

Is this what's happening?

You can also try lowering the idle speed down to ensure that the mechanical advance is not affecting the timing as well.