[lethal-428-lemans]

I have my 400 running pretty good but I want to get her spot on. I get some chatter or pinging when I start to step on it.

I picked up a digital advance timing light to set it spot on. I unplugged the vacuum advance and blocked it off. Then with the car running I ran the light to 28 degrees and my mark was on 0. ( I am assuming this is the right way to do it ) but when I plugged the vacuum advance back to the distributor it took my timing to 50 or 51 degrees.

Am I using this light right ? I was thinking Pontiacs like 32 degrees. Do I need to bump the 28 up to 32 or back the 51 down to 32 ?

Thank you in advance for any help.

[track73]

You didn't allow for the centrifugal advance. Set the timing to 32-36 at about 3000 rpm. The centrifugal should be all in by then,

[Schurkey]

What RPM was the engine at when you timed it? You need to have the centrifugal advance "all in". Depending on the weights and springs, it might require 4500+ rpm to get the centrifugal fully extended. Typically about 3000 rpm "all in" works well for a performance engine. Vehicle weight and gearing will affect how fast the centrifugal needs to come in.

"Total" timing in the middle-30s is pretty normal. "Total" timing is initial + centrifugal, but DOES NOT INCLUDE VACUUM ADVANCE.

Add another 10--20 degrees for the vacuum advance = mid-40s to mid-50s.

Many vacuum advance canisters have WAY TOO MUCH advance built-into them. They can be limited to less advance by various means, or replaced with a canister that is engineered to have less travel (less advance.)

Example for limiting vacuum advance:

[lethal-428-lemans]

So do I let the vacuum advance hooked up and run it to 3000 rpm then check it again ?

[track73]

There's a vacuum canister from a 427 Chevy that has only 10 degrees of advance. I think Suntuned recommended it. I bought one on EBay and another from Rock Auto.

[rohrt]

Lets start over.

1. What is the vacuum source? Ported or Manifold? Manifold has a vacuum at ide
2. What distributor do you have? Points or HEI?
3. Disconnect your vacuum can and plug it.
4. See what your timing is at idle
5. Rev up the motor past 3K and see what your timing is
6. At idle connect your vacuum can back up to a manifold source and record timing.

Get this info first before you make any changes.

[steve25]

Stock weights and springs will not bring in all centrifugal by 3000 rpm so don't be looking for that!
Pinging when diving into the throttle most times is from the vac advance not dropping off fast enough.

[lethal-428-lemans]

I'm pulling vacuum from the manifold. Hose from manifold to advance on the HEI distributor.

At idle I advance the light to 28 degrees and my mark is on zero on the timing cover.

At ideal with the vacuum hooked back up the light goes to 50 51 degrees to put the mark on zero.

When I run the idle to 3000 do I want the vacuum blocked off again or do I want it drawing on the advance ?

[Bruce Meyer]

Originally Posted by lethal-428-lemans

I'm pulling vacuum from the manifold. Hose from manifold to advance on the HEI distributor.

At idle I advance the light to 28 degrees and my mark is on zero on the timing cover.

At ideal with the vacuum hooked back up the light goes to 50 51 degrees to put the mark on zero.

When I run the idle to 3000 do I want the vacuum blocked off again or do I want it drawing on the advance ?

Keep the vacume advance plugged when setting timing. Shoot for 34-36 total.

[Formulajones]

You want the vacuum advance unplugged (inoperative), run the engine up to where the distributor stops advancing. Could be 3,000 like others suggested, could be more or less depending on what springs are in it.

While it's at the limit of the centrifugal advance set the total at say....32 degrees with your advance timing light (zero on the balancer)

Let the engine come back down to idle and check. Depending on how the distributor is setup you should see anywhere from 10-18 degrees initial at idle.

Then plug the vacuum advance back in and see what that does.

[Bruce Meyer]

Originally Posted by Formulajones

You want the vacuum advance unplugged (inoperative), run the engine up to where the distributor stops advancing. Could be 3,000 like others suggested, could be more or less depending on what springs are in it.

While it's at the limit of the centrifugal advance set the total at say....32 degrees with your advance timing light (zero on the balancer)

Let the engine come back down to idle and check. Depending on how the distributor is setup you should see anywhere from 10-18 degrees initial at idle.

Then plug the vacuum advance back in and see what that does.

Oops I should have been more clear. Yes Formulajones is right. Make sure vacume advance is not hooked up. When I said plugged I didn't mean plugged in. I meant plugged so vacume cant get to it.

[Joe's Garage]

1) Remove the distributor cap and rotor and then take out one of your advance springs inside the distributor. If you have access to one of the aftermarket 're-curve kits' you could always install both the really light springs to do the same thing. Put the rotor and cap back on so you can start the engine.

2) Disconnect the vacuum hose from the vacuum can on the distributor and PLUG it .

3) Hook up the timing light and set your dial-back at the total amount of advance you are wanting the engine to have (ie: 36 degrees).

4) Have a helper start the engine, so you can make sure the timing light cables stay out of the fan and belts.

5) Run the RPMs up until the timing stops advancing - with the spring removed it will only be 1,500 or 2,000 rpms.

6) Check with your dial-back and see what your TOTAL centrifigul advance is. Adjust the distributor and re-check if needed to get to the total you want.

7) Shut the engine off and reinstall the 2nd spring in the distributor.

8) Restart the engine and check your initial timing with the dial-back feature. Vacuum hose is still disconnected.

9) Record what your initial timing is in order to get the total you wanted. That way you can just set the initial timing (at idle) in the future and not go through all this again.

10) To check the timing WITH vacuum advance, hook the hose back up and use the dial-back feature to check either your initial or total timing with the vacuum working.

Good luck!

[Formulajones]

Originally Posted by Bruce Meyer

Oops I should have been more clear. Yes Formulajones is right. Make sure vacume advance is not hooked up. When I said plugged I didn't mean plugged in. I meant plugged so vacume cant get to it.

I think you and I were typing at the same time. I read your post and understood that's what you meant.

[Lee]

1. Disconnect vacuum advance to distributor, plug the open end of the hose.

2. With engine at idle, adjust the timing to whatever arbitrary number you like, say "12" to get started.

3. After tightening down the distributor, recheck to make sure the timing didn't move a little bit.

4. Reconnect the vacuum advance.

5. Write down the timing setting, and go for a drive. Record how it acts and responds.

If you like how it runs, then leave it alone. Otherwise add 2 degrees and repeat. Play around until you find what works best for you and your motor. I've seen motors that liked anything from 4 AFTER TDC to 24 BTDC.

I've NEVER worried about "total" timing. Your timing light can be off, the timing marks can be off, and you may not even have ALL the advance taken out at the rpm you choose. I also don't like being bent over a motor with my head where I can see the timing marks with the engine running 3000+ rpm and the fan and accessories whirring around looking for a finger to whack.

If you add one degree to your initial at 700rpm, then you are adding one degree to your total at whatever rpm that may occur. Make the job easier, not harder.

[dmac]

Unless your initial, vacuum, and mechanical are all exactly right, you will likely need to either compromise a little or change/fix your mechanical timing or advance timing. Your engine is going to like a particular initial timing for starting, another at idle, just like it likes a particular partial throttle timing and a particular cruise timing. The factory equipment was able to give a bit of flexibility and was a good enough compromise for most drivers.

Getting one of those setting right by adjusting a couple degrees at a time may leave the other settings out of optimal and give you overheating issues at idle, or hard starting. Getting all of the timing settings PERFECTLY optimal will likely take the adjusting of weights, springs, vacuum unit. For a daily driver mild motor where getting the max out doesn't matter, IF the factory equipment is still working right after 40-60 years, you need to verify by more than just advancing until it runs good under whatever condition you test for by driving it around for a while.

[lethal-428-lemans]

I unhooked and plugged of the advance hose.

I ran the rpm up to 3100 and set the timing to 32.5 degrees . Then at idle it was 20 degrees. When I reinstalled the vacuum line it went up to 40 degrees at idle.

Do these sound like good numbers ?

[Schurkey]

Originally Posted by lethal-428-lemans

I'm pulling vacuum from the manifold. Hose from manifold to advance on the HEI distributor.

At idle I advance the light to 28 degrees and my mark is on zero on the timing cover.

28 degrees of advance at idle, with the vacuum advance disconnected is WAY TOO MUCH.

Originally Posted by lethal-428-lemans

At ideal with the vacuum hooked back up the light goes to 50 51 degrees to put the mark on zero.

51 - 28 = 23 degrees of vacuum advance. This is probably too much.

Originally Posted by lethal-428-lemans

When I run the idle to 3000 do I want the vacuum blocked off again or do I want it drawing on the advance ?

DO NOT have the vacuum advance connected when checking total timing.

You should not be checking the total timing at 3000 rpm unless that's where it stops advancing. You may need 4500+ rpm before the centrifugal stops advancing. If so, you'll want to recalibrate the distributor so that the advance comes in sooner (depending on vehicle weight, power level, and gearing.)

[Schurkey]

Originally Posted by lethal-428-lemans

I unhooked and plugged of the advance hose.

I ran the rpm up to 3100 and set the timing to 32.5 degrees .

Did the centrifugal advance stop advancing at 3100 rpm?

Originally Posted by lethal-428-lemans

Then at idle it was 20 degrees.

A bit higher than I'd like. I hate seeing initial go over ~15.

Originally Posted by lethal-428-lemans

When I reinstalled the vacuum line it went up to 40 degrees at idle.

20 degrees of vacuum advance is probably too much.




"I" would want 10--15 degrees initial, about 20--25 of centrifugal advance, for a total of 30--35 degrees, and maybe 10--15 degrees of vacuum. But all of this needs to be tuned to fit the application.

[lethal-428-lemans]

How do you know when the centrifugal advance stops ?

[Schurkey]

Originally Posted by lethal-428-lemans

How do you know when the centrifugal advance stops ?

When the timing mark stops advancing.