Unsteady timing mark

mpt said:

I own a 1981 Bayliner 3270 powered with twin Volvo Penta BB140A's. Both motors have Pertronix that I installed over 12 years ago. Both run great with the Pertronix! Yesterday I was checking the timing on both engines starting with the starboard. Timing was around 11 BTDC which I lowered to 8BTDC to meet factory specs at 900 RPM on idle after warm up.
You need to be also looking at the progressive and total advance.
See your OEM specs for this..

When I started to check the timing on the port engine, I noticed the mark flashing up and down a couple degrees from the timing notch on the fly wheel! I adjusted it close to 8 degrees BTDC to match starboard engine. Over the years, the port engine always ran the smoothest of the two, even when I checked it with the timing light it was doing the same erratic flashing and not steady like the starboard engine timing mark!
Inside of the distributor will be your flyweights and governing springs.
If the governing spring value is rust compromised, you may see an erratic spark timing event at below 1,000 RPM.
These springs are to prevent the flyweights from advancing until above approx 1,000 RPM.
From that point, they will then allow the system to advance progressively up to what's referred to as the "Full In" advance RPM.
Again, see your OEM specs for this.

In order to correctly replace the springs, the distributor should be run on a Sun, Allen or King distributor machine, and by a professional who knows how to operate it.



So questions are- could it be the Pertronix?
I would say NO.

Coil?
Again, I would say NO.

Timing Cog belt?
A belt that is not indexed correctly will give you other issues.

Even though port engine runs smooth!

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mpt said:

Years ago when I installed the Pertronix, and after removing the points and condensor I didn't remember seeing any fly weights or springs? I looked at blow up diagrams of the distributor in marinepartseurope.com for BB140A and didn't see any springs or fly weights either.
The flyweight system is not visible in the schematic.
(see below)


Maybe there is no advance mechanism for that application?
In order for the distributor to NOT have flyweights and governing springs, it would need to be an EST unit.

Look again...... they have to be there!

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