erratic timing mark
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 1,128
Likes: 4
From: Upland Ca
erratic timing mark
Hi guys, What causes a timing mark to be erratic? I have a fresh motor, new MSD A6L box and MSD pro billet tach drive dist. At and idle or 2500 the mark is jumping around. Thanks for the advice. Lee
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Most likely cause is bad harmonic damper ... rubber bad ... outer ring (with mark) is slipping in relation to inner hub (keyed to crank). Other possibilities: wore out timing set, worn dist gear, sheared dist gear roll pin.
Melting Slicks
Joined: Feb 2003
Posts: 2,529
Likes: 27
From: Auburndale Florida
2025 C2 of the Year ('64-'66) Finalist - Unmodified
St. Jude Donor '03-'05-'06-'07-'09
Mine does that!!!!
Figured it was the inductive pickup on the timing light. Usually have to move it around to get a signal
Figured it was the inductive pickup on the timing light. Usually have to move it around to get a signal
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 1,128
Likes: 4
From: Upland Ca
Jack, Thanks for the feed back. I'm checking and trying to eliminate possible causes. Motor has new balancer, dist gear, timing set. I'll pull the dist and check the roll pin. Again, thanks. Lee
Pro
Joined: Nov 2004
Posts: 607
Likes: 0
From: North Alabama
Is your vac adv plugged in to the port side or the manifold side of the carb? I ask because if the answer is manifold, there is a possibility the vac can is not coming all the way in for one reason or another.
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Melting Slicks
Joined: Oct 2005
Posts: 2,056
Likes: 8
From: Redruth Cornwall
Originally Posted by yellow 72
Some inductive lights don't work well with MSD boxes.
Snap-On and Craftsman dial back types are two that do.
Snap-On and Craftsman dial back types are two that do.
Work with the simple stuff first. If all is new on engine then hopefully not your new harmonic balancer....unlikely, but not unheard of.
Check your timing light specifications and on another vehicle with a similar ignition setup.
Thread Starter
Burning Brakes
Joined: Feb 2003
Posts: 1,128
Likes: 4
From: Upland Ca
Thanks all. I will double check all of these things. Even though all of these things are new with a fresh engine it could be any one of these things.
I'm using a Innova timing light. First thing I will do is check timing with a stock number 1 wire VS the MSDs on it now. This timing light works great on all my other cars.
I'm using a Innova timing light. First thing I will do is check timing with a stock number 1 wire VS the MSDs on it now. This timing light works great on all my other cars.
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,508
From: Little Rock AR
It's the MSD. 
MULTIPLE SPARK discharge at low RPM. You may need a different timing light to work with that MSD.
It is better to set the timing at the top of the curve anyway. You only have time for 1 spark at that point.
-Mark.
MULTIPLE SPARK discharge at low RPM. You may need a different timing light to work with that MSD. It is better to set the timing at the top of the curve anyway. You only have time for 1 spark at that point.
-Mark.
Pro
Joined: Nov 2004
Posts: 607
Likes: 0
From: North Alabama
Originally Posted by GDaina
Vacuum leak?
"...A tuning note on this: If you choose to run straight manifold vacuum to your vacuum advance in order to gain the
additional timing advance at idle, you must select a vacuum advance control unit that pulls in all of the advance at a
vacuum level 2" below (numerically less than) the manifold vacuum present at idle. If the vacuum advance control
unit is not fully pulled in at idle, it will be somewhere in its mid-range, and it will fluctuate and vary the timing
while the engine is idling. This will cause erratic timing with associated unstable idle rpm...."
