Timing advice

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Orionsax7

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So after educating myself on all the useful timing articles I could find on the net and buying an advance timing light(FINALLY) I just got back in from setting the timing on my 1971 Demon 318 with all the bolt-ons and mild cam. Daily driver.

I checked where it was set first and then I realized that the vacuum advance was plugged into MANIFOLD VACUUM at the base of the Holley carb. I checked the timing and it turned out to be 25 at idle, if I understand correctly. (The timing light set at 25 had the timing mark right at zero).

I disconnected it and plugged the line and set the timing to 5 BTDC. Reconnected the distributer to the PORT VACUUM and the car runs good, seems to idle better now too. Only thing is now that I have it set, I'm getting a slight but constant puff of white smoke from the left tailpipe that I don't remember being there before. Any ideas what this might be?

I'll be checking the vacuum as well as soon as I get my vacuum gauge in the mail probably today or tomorrow.
 
My 340 originally ran at 5* with points. More than that , it pinged like a bastard. With electronics, I know run it at 13* initial and 33* total not including vaccum. Most 'A' engines like around 32* to 36* total. Just keep increasing it until it starts to ping, (with vac plugged), then back off a bit.

The white smoke may be caused by a lean carb condition. To run the higher timing numbers, a lean carb will cause pinging also. The two really go hand in hand.

Since I removed the heat riser from my exhaust manifold, I now get that white smoke during warm up, but eventually goes away. I believe that happens because its lean until it warms up smooths out. Not quite sure on that though.

Jim
 
it may just be heat in the exh that is burning stuff away that got built up in it when the timing was so far off. Drive it, see if it stops after a few miles. You may want to take it out on the highway and flog it a little...
 
You mentioned that you have a mild cam in that engine so you'll need to find the sweet timing spot for that particular cam in conjunction with your other bolt-on goodies. I would say that the 5* is not enough advance in your case. Try reving the engine to 2000 RPM, check the total advance there, then do the same thing at 3000 RPM, and see what you get for total timing, with the vacuum line disconnected and plugged of course. As previously stated, most small blocks like between 34* and 38* total. Once you're set in that ballpark, then just re-check your timing at idle again. I bet it will be more than 5* - probably 14 to 18*. :)
 
Cool, I'll do that tomorrow when I get home from school. Thanks for the help. I think you were right about the smoke because now that I've driven it to work and back I didn't notice it when I got home. What I do notice now is that it seems to run a little hotter now?? I'll keep my eye on it tomorrow.
 
OldVart said:
You mentioned that you have a mild cam in that engine so you'll need to find the sweet timing spot for that particular cam in conjunction with your other bolt-on goodies. I would say that the 5* is not enough advance in your case. Try reving the engine to 2000 RPM, check the total advance there, then do the same thing at 3000 RPM, and see what you get for total timing, with the vacuum line disconnected and plugged of course. As previously stated, most small blocks like between 34* and 38* total. Once you're set in that ballpark, then just re-check your timing at idle again. I bet it will be more than 5* - probably 14 to 18*. :)
Click to expand...


DITTO
 
If you have made mods like a cam carb and exhaust the factroy timing in the distributor is not going to me ideal for the engine any more. The total mechanical advance numbers people have sited are good ball park numbers but it will take getting the car on a dyno or many runs down the drag strip to zero in on the best setting. The same for the rate at which the mecahnical advance comes in. The ball park for that is some where in the low to mid 2000 range. Most stock distributors have it well past 3000 and some of the early 70's emission distributors it won't all be in to 4000 or more. Vacuum advance can be tweaked by driving the car but total advance with vacuum should be in the low 50 degree range.

If you are really interested in dialing in your distributor here is how I would approach it.

1. Don't worry about initial or total timing for this step. With your vacuum advance disconnected. Using your timing light and a tach increase the rpm until the timing stops advancing. If it's in the 2000-2500 range you are good to go. If it's over 3000 rpm you need to change the springs in the distributor. There are usually one heavy spring and one lighter spring on the counter weights under the points/pickup. If you replace the heavy spring with one of the light springs from the Mopar Performance spring kit that should get you back into the 2k to 2.5K range. Using both light springs and the advance will be all in just above idle which will likely cause detonation problems. Optimizing this will make power improvements in the mid range.

2. This step you will be finding out what the engine wants for initial timing and you will need a vacuum gauge. Increase the initial timing is small increments (2 degrees or so) until the manifold vacuum stops increasing. Rember to reset the idle speed back to what it was when you started after each increase in the timing. Once you find the initial timing for max advance check to make sure the engine starts OK. You could have a situation where it wants the timing to be far enough advanced that ignition will fight the cranking of the engine. If you have this situation you will need to back off a couple of degrees at a time to find the point the engine starts well. You will likely find that the engine is happeist with initial timing of 10-15 degrees. Optimizing this setting will improve the throttle reponse off idle dramtically.

3. Now using your set back timing light rev the engine until the timing stops advancing, now see where the total timing is. If it's in the 32 to 36 range your are golden but it's likely a lot more if the distributor is from a low performance or early mid 70's engine. If it is then you will need to rework the slots in the advance mechanism or look for a distributor with less timing in the slots. The top half of the shaft with the slotted piece that the weights act on should be stamped with the number of distributor degrees of advance, double this number for crank degrees. If you aren't inclined to get this much into the distributor tweaking then just set the total timing in the 32-36 range and take the hit on not having optimal initial timing.

4. Now for vacuum advance. The arm on the vacuum pot is stamped with the distributor degrees of advance, again double this number and add it to the total advance number you have. If it's in the low 50's you are good to go. If it's not then you will need to pick one up that has the correct number of degrees.

5. Most all mopar vacuum advance modules can be adjusted by inserting a small allen wrench into the port the vacuum line connects to. The adjustment sets the amount of vacuum at which the pot starts moving and the vacuum level to reach max advance. Adjusting this is a trial and error excersise. You want it to come in ASAP without causing any part throttle detonation. Getting this dialed in will maximize your mileage at steady state cruising and with $3/gal it's well worth the time.
 
NEVER RELY ON TIMING TAPE OR DAMPER MARKS!!!
At least, not on a stock, unknown damper.
In order to get the proper markings onto the damper, you need to use the dial indicator method, on a KNOWN GOOD damper, to lay out the timing marks on the damper. Even then, with stock dampers, it's only "close", since rubber allows the outer ring to move.

Here is another "ballpark" method of timing an engine, but it seems to work:

Get a diagnostic tach (your timing light should have one), leave the distributor slightly loose, then rev the engine to @ 2,000-2500 RPMs. Listen closely to the exhaust and watch to see if the engine is twitching, or the exhaust is "fluttering".
While at this RPM, adjust the timing until the engine runs smooth, usually you need to back it off (retard it).

What this does is get the timing at or below the point of fuel detonation, though it'll change slightly the next time you add fuel.

I time all of mine with this method and it's never done me wrong.

Also, use the lightest centrifugal advance springs you can, in the distributor.
The sooner you can get all the timing in, up to the fuel's detonation point, is always best for overall performance.

Mark.
 
Some great info here. This thread should go to the tech archive section. :thumblef:

I do not have much to add, except for a caution on using dial back timing lights with a multi-spark CD ignition box (like MSD). You will likely get false readings below 3000rpm. This is about where the ignition switches from multi-spark to single spark. MSD recommends using a non-adjustable timing light.
 
Timing doesnt affect detonation. Poor chamber design, poor fuel, or excessive cylinder pressure does..Least that's what all the books say. If you have a stock distributor, you wont be able to get the total to 35 unless you take out all the initial. The centrifical in most setups from the factory has too much in it. As far as stock balancers, they are usually between 2-5* off if checked with a piston stop. (which is the easiest, cheapest, and fastest way to check) You can check yours, remark the balancer, and the add a timing tape, and you're miles ahead of most guys. The outer ring can move if it's on its way out, but wont if it's at all intact. They are usually put together incorrectly, that's why they are off.
A new timing curve is easy. Tape $3, spring pkg $5, muffler shop to weld up slot in advance plate $20. The rest is your labor. Same as FBO, similar to MPs adjustable distributor. You'll need a piston stop (old spark plug, tap set, and a bolt), a rat tail file (to re-shape slot after welding), some needle nose pliers (for spring change and clip removal) to access the advance plate, the allen wrench for the vaccum pod (17/3 or close?), a rag, and some brake clean, plus your normal timing light.
 
I should have mentioned nefore but the distributor I have was part of the Mopar electronic ignition conversion with the orange box. I have since changed the CPU but the distributor is the same. Anyone know how much advance is built into those?

-Alex
 
Wayy too much, usually. But, they can be adjusted. the newer ones (say less than 3-4 years) have allen head screws to lock the advacne plate at a certain point, so you can control the centrifical advance amount. The slot isnt marked, so I just use fractions..Say if you measure the centrifical with the timing tape and light (that's total minus initial) and it's 30*. You want to run 38* total, but want 18* initial. So, you need to get the advance plate set to limit the centrifical to 20*. That's 1/3 off, so I would loosen the screw, move the stop to make the hole 1/3 shorter than it is, and recheck total. (dont forget to do both slots on the plate, otherwise it may move on you later...) If you had say 5* initial, and moved the plate limiter screws, then you will only have 25* total timing, until you add the additional initial to it, so dont get confused if you check total right after, and it comes up very low.
 
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