86' Force Timing issue

[iwaterdave]

I'm new to boat outboard motors. I wanted to set the timing and idle speed according to the manufacture repair manuel. I bought a timing light that says it can switch from 2 cycle and 4 cycle engines. I connect it and it shows the idle speed jumping about 200 rpm up and down. (1000-1250) Also is not consistant with flashing on the mark. It seems to be jumping around from the desired mark.
My question is does this sound like I have the wrong kind of timing light or is this an engine issue I still need to fix prior to setting these two items? In full disclosure I do notice the engine hickuping mildly but not too bad when idleing.

Thoughts?
Possible causes?

Thanks,
Dave