Timing walking/jumping around

[brickyard69]

What would make timing walk.

It is a brand new 383 with an HEI.

The initial timing (with vacume dis-connected) seems to walk between 15 and 25 degrees.

I have checked the mechanical advance, and everything move fine (new distributor).

When I connect the vacume canister to adjust it, the timing advance kicks in afer a few seconds and stays too high.

I have sine dis-connected the vacume advance but still get this walking.

Also, when I set full advance, it jumps between 30 and 40 degrees.

Any suggestions?

[Norwoodx55]

Is it a roller cam motor? If a cam button (or another form of cam retention) isn't used, the cam will walk forward and back which screws with the timing.

[sporter]

Another cause for this problem is too much shaft clearance between the distributor body and the gear. They make shim kits to reduce the clearance to .010 for steady timing. My son's Proform HEIs for both his sbc and his Pontiac 455 had over .050 clearance out of the box and had to be shimmed.

[astroracer]

You say "brand new" 383... Is EVERYTHING brand new? How about the harmonic balancer? If you have a used one on there the outer ring may have become unbonded to the rubber... That will cause the problem you are seeing also.
Mark

[6'9"Witha69]

In some way, I have experienced all 3 of the above in my life.

number 4. Double check the weights/springs and retainers on the mech advance. I have seen times when the plastic bushings on the weight post was too small and allowed the weights to move around too much. Never saw 10 degrees, bout half that, but still an option. I would say look at the shims on the dist next as that is a very likely culprit.

[brickyard69]

I swapped HEIs and that seamed to correct the "wandering at idle.

Now the problem is that I have the initial set at 15 degrees and when I take it to 3000 rpm the timing jumps to 90 degrees.

The advance springs are the silver ones and evrything works normal on it.

I did not think mechanical advance systems could advance that much.

Does this seam correct?

My next step is to try different springs.

[LowBuckX]

try a new modual

[brickyard69]

I just installed a new MSD modual.

The one with the built in rev limiter.

[brickyard69]

Let me clarify. I installed it in this distributor with no problems.

[LowBuckX]

I just installed a new MSD modual.

The one with the built in rev limiter.

IM sorrry to hear that.. Those modules are problem prone.

And those super high perf moduls you can get from everywhere with differand manufactures stickers on the well THEY ARE THE VERY SAME AS A TP45 NAPA, Echlin, Borg-Warner, Mallory, Standard Blue Streak and Sorenson, as they are all owned by the same parent company now, Standard Motor Parts

[CarlC]

Also check to make sure that the weight support plate is secured to the shaft. It drove me nuts for months until I found it.

[brickyard69]

I replaced the MSD unit and it works fine.

The only reason I wanted it was for the built in rev limiter.

I guess I just waisted $85.

[LS6 Tommy]

I swapped HEIs and that seamed to correct the "wandering at idle.

Now the problem is that I have the initial set at 15 degrees and when I take it to 3000 rpm the timing jumps to 90 degrees.

The advance springs are the silver ones and evrything works normal on it.

I did not think mechanical advance systems could advance that much.

Does this seam correct?

My next step is to try different springs.

It's a stock HEI? Is that with the vacuum advance? They have LOTS of mechanical advance, up to almost 40* and the vacuum can can have a lot, too. Springs won't change total advance, only when it comes in. If it's a stock HEI with vacuum, drop your initial to around 4* and see what happens.

Tommy