The mechanism that advances the timing is a pair of weights and springs.
It's been a while but if I remember they are under the plate that the points
are mounted on in chevy distributors. The mechanical advance works by
twisting the top of the distributor shaft as the weights sling out when the
rpm increases. You can usually feel it by grabbing the rotor and attempting
to twist it. Another problem that can cause timing changes is a worn out
upper bushing in the distributor. When the bushing is worn it allow sthe
shaft to move side to side which can change the gap and that changes the
timing. You check the upper bushing by trying to move the shaft from side
to side. Turn it so the points are open and then you can watch the points
to see how much of an effect you are having on them.

On the off chance you have a vacuum advance it is a vacuum diaphram on the
side of the distributor with an arm that turns the points plate. Vacuum
advances are not common on boats.

If the advance is having problems then just converting to electronic may not
be the answer. Some conversions still rely on the mechanical advance. They
just replace the points with a trigger and a cd module. Unless you replace
the distributor with an electronic one such as the thunderbolt setup. Then
the advance is electronically controlled in the cd module.

Distibutors are repairable. It's easier out of the engine. Set it on tdc
with the rotor pointed to the #1 plug wire before you remove it.


"JamesE" wrote in message
oups.com...
I have a 1988 Sting Ray with a Mercruiser 3.0 liter. Lately I have
been having some trouble with the timing. I will set the timing and
it will start right up and idle well, but then after I speed up and
slow back down it will stall and be very hard to start, I was almost
stranded the last time I went out. Then if I adjust the timing again
I can get it running again. I am no expert on the ignition system but
I know that the timing is supposed to advance itself as the rpms go up
and then retard when they drop back down. Right now I have the points
style distributor in the boat and I think that whatever changes the
timing with the rpms is malfunctioning because when I adjust the
timing again it will start. So I have decided that in order to
eliminate this problem I am going to switch over to electronic
ignition. My question is do you think just using the conversion kit
which just converts the current distributor to an electronic one would
work? Has anyone used these kits? I am looking to do this as cheap
as possible. But since I am already having trouble with the ignition
I am unsure that the conversion kit will fix it and I will have to buy
the whole electronic distributor instead. I would like to buy just
the conversion kit unless you guys think that that won't help because
I am already having problems. So do you think that the conversion kit
will do or should I buy the whole electronic distributor? Thanks,
James.