Advanced timing causes engine to Skip?

[Wajulia]

I took the advice that I read in this forum and set my ignition timing to 12 deg BTDC. When I did, it could feel one of the spark plug wires tug (number 8 I think). When I was finished, the car seemed to have a very small skip that it didnt have before. Also had idle issues that where new.
I went to my local drag stip and I lost about 3 tenths in 1/4 mile times -- that was not what I was hoping for.

Do you think I damaged a spark plug wire? Would retarding the timing cause any of these symptoms. I thought the only possible issue would be pre-detonation -- no sign of it.

 

[Vettehead Mikey]

Arbitrarily setting initial timing to 12 degrees as a 'one size fits all' sounds a little strange. Not sure why someone would recommend that.

It is possible that you pulled a plug wire loose when resetting the distributor and are actually running on 7 cylinders.

I doubt your engine has been damaged, but I would restore the previous settings and check the HT wires before playing around any more.

 

[joe paco]

Arbitrarily setting initial timing to 12 degrees as a 'one size fits all' sounds a little strange. Not sure why someone would recommend that.

It is possible that you pulled a plug wire loose when resetting the distributor and are actually running on 7 cylinders.

I doubt your engine has been damaged, but I would restore the previous settings and check the HT wires before playing around any more.

I agree. If all we are doing is setting timing and not modifying, you can easily put another timing mark across the vib dmper -if you measure the circumference carefully- that is CLOCKWISE from the original timing mark, which equals 38 degress of the total circumference, of 360 degrees. Then, you can use the light, and increase rpm until total centrifugal timing is in -or all out, whichever- and align the new mark with the zero on the tab.
this is identical as setting static timing using the tab, but "in addition to." or, when in doubt, use factory specs and set static timing, as vettehead said.

have not messed with this for about 40 years, but that's how we used to do it. the timing at idle rpm will be 6-12 degrees, depending on your distrubutor, but the total on that vintage Chevy motor was 36-38.

 

[Peer81]

Don't forget this is a computer controlled HEI, so you can't set total timing by disconnecting the vacuum line and rev above 2500-3000 rpm. You can only set initial timing.

And 12 degrees is still very save so like you say, check the sparkplugs and wires. She should be running better at 12 degrees than on 6 degrees with the original old design heads.

Greetings Peter

 

[joe paco]

Don't forget this is a computer controlled HEI, so you can't set total timing by disconnecting the vacuum line and rev above 2500-3000 rpm. You can only set initial timing.

And 12 degrees is still very save so like you say, check the sparkplugs and wires. She should be running better at 12 degrees than on 6 degrees with the original old design heads.

Greetings Peter

I did forget! My info is useless unless you have a centrifugal advance. I have a 91, but my experiecne is with pre computer Chevys. Sorry for the erroneous info.

gracias, joe

 

[GerryLP]

Yes, setting the initial timing to 12 degrees worked best in my engine. But sounds that the way you adjusted the timing was by rotating the distributor?!?!?!....am I misunderstanding you? Also, when setting the timing, the four-pin wire connector must be separated from the distributor.

GerryLP:cool

 

[Wajulia]

Yes -- I rotated the distributor. But it would not rotate enough to get to 12 degrees because it was pulling on the wires -- so I did what anyone would do -- turn it harder:eyerole. Thats why I am thinking I trashed a wire. I am not sure which wire was being pulled because I still have the noise shield on the distributer and it does a good job of hiding most of the wires so I couldnt see what was being tugged.

As for the connector -- a Bubba in a chevy dealer about 20 years ago had problems disconnecting it so he cut it off!ad!!!!! The wires are merely twisted together -- I did disconnect them while changing the timing. I am a little worried that I swapped a wire putting back together. The colors are a little faded, looked like a pink wire with a white stripe and a pink wire with a black stripe. But I could have gotten them backwards.

I am going to get a new set of wires this weekend (they are 20 years old and should probably be replaced anyway) and then check the service manual to assure I have the wires connected correctly -- I will let you know if it gets any better.

 

[GerryLP]

Wajulia,

On the computer-controlled L81's, the only timing change you can do without altering the computer code or ignition module's values, is to alter the initial timing. To change the initial timing,

1) you most find top-dead-center on the number one cylinder on its compression stroke.
2) Then, mark the #1 lead wire electrode on the rotor cap to the base of the distributor.
3) rotate the dampener slightly to align the 12 degree mark on the timing index plate with the " zero" groove on the dampener.
4) Loosen distributor clamp bolt.
5) rotate distributor base's mark (from step 2 above) to align with distributor rotor
6) if the distributor rotor cap's wire connector's end (the one with BAT, TACH, POS, and NEG connectors) is not pointing towards the driver's side fender, then you may have to do the following:
A) remove bolt and clamping bracket of distributor
B) lift distributor enough to allow distributor rotor turn freely
C) re-index distributor by lowering it into its bore and while engaging cam gear cogs with
distributor shaft cogs so that when completely seated, the rotor aligns with distributor's base mark.
7) reinstall clamping bracket and bolt and snug down (I use some anti-seize compound on this bolt to avoid problems next time with the threads).Also, NAPA (NAPA know how, NAPA know how!!!... ) has the GM 4-pin connectors, metal pins, rubber seals, and even the tool to help you make a new and easy to disconnect point for the distributor. I hope this helps.

GerryLP:cool

 

[Wajulia]

So I changed 4 of the spark plug wires last night and the skip seems to have gone away. What a PIA changing the passenger side wires -- YOU HAVE TO REMOVE THE STARTER! I will attack the drivers side today.


Gerry -- The tack wires are pointing towards drivers side door, not the fender -- I see you believe I should pull the distributor and move it a tooth -- is that necessary?

I will look for the connectors at NAPA. Let you know how it goes

 

[Peer81]

Don't move the distributor a tooth if you don't know what you're doing and what the settings are right now.
The last time I changed the spark wires I didn't have to remove the starter, but lucky for you the drivers side is much easier

Greetings Peter

 

[GerryLP]

....Gerry -- The tack wires are pointing towards drivers side door, not the fender -- I see you believe I should pull the distributor and move it a tooth -- is that necessary? I will look for the connectors at NAPA. Let you know how it goes

Necessary? No. But is the best configuration if you want the wires to reach and follow the stock configuration/routing. When I replaced the wires on my car (at the time when I overhauled the engine), I installed Acel's 300 ohm/foot wires in it to delay that task as long as I could. I agree, it is a PITA ad

 

[Wajulia]

Gerry

Do you know how to find the connector info -- my NAPA guy could not find anything.

 

[GerryLP]

Gerry Do you know how to find the connector info -- my NAPA guy could not find anything.

I just called my local NAPA (1-505-892-4376), and they told me that they are listed in their Wire and Cable catalog, on page 20.