timing fluctuation and dizzy curve

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71d3m0n

71d3m0n

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when i check my total timing it jumps around but my initial is steady .
i have a mp dizzy it has very light springs . i just learned that there is a measurement for the reluctor .008 but havent done it yes im working out of town . i heard i need a brass feeler guage for that is that true? whats ur thoughts on timing mark?
 
Yes, you need a nonmagnetic (brass or other non-steel material) feeler gauge to check the reluctor-to-pickup air gap. However, that isn't causing your fluctuating timing. The light springs in the MP distributor make it a drag race piece, nowhere near optimal for street usage, and one of the effects of the light springs is bouncy ignition timing especially at (and just off) idle. Another cause of bouncy timing is a slack timing chain.
 
the timing marks are pretty stable at idle just total is what im havin issues with. where would i find a brass feeler gauge and what would i notice if that gap is wrong?
 
Poor ignition performance if the gap is wrong. Brass feeler gauges are included in good quality feeler gauge sets or can be had individually; do a Google search.
 
I have just the opposite problem with my motor. Steady at full advance but jumps around at idle. I just put heavier springs on the dist cams a couple days ago and it's still the same. They weren't the real heavy ones but one step up from the lighest.
 
Pop off the distributor cap and give the rotor a turn in the direction of distributor rotation, then let go. If it does not snap smartly all the way back to its original position, you've got mismatched springs in the distributor (end loop too big on the lightweight spring). If no problem found here, check for a slack timing chain.
 
motor is fresh only like 1000 miles at most on new chain hope its not that.
 
There are several things that can cause timing jump or "spark scatter."

Not in order of any particular importance or popularity:

Worn cam gear or even worn cam bearing

Worn intermediate gear, damaged or bent

WORN BLOCK BUSHING

Wear at the tang drive between gear and distributor

Wear of several sorts in the distributor, IE shaft bushings, advance mechanism, something loose, worn/ loose / missing parts in advance plate

One obvious first step, if you can, is try a KNOWN GOOD distributor. This would be, for example, out of a friend's running setup in which you have checked the timing as you did on yours, and know the dist. is good.

Many articles have been written since I had my first Mopar in '70. Performance guys have been fighting spark scatter on Mopar HP engines for years. The short answer is, the distributor drive mechanism on SB, B, and RB engines is not exactly an optimum design.

Depending on what you are using for an ignition box, or electrical problems (like a bad diode in the alternator) "static" IE electromagnetic interferance in the wiring harness(s) can cause false triggering, and in fact, is one reason that MSD does NOT recommend solid core wires on high output systems.
 
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