Hi there, welcome to iboats!
Are you aware that there is a special procedure you need to do before setting the Initial timing @ - 2 degrees?
You'll need to get yourself a timing test lead (shunting tool) Volvo part number 885163 available here at iboats
CABLE - Volvo Penta 885163. It will look like this,
Volvo Penta Distributor Timing Shunt Tool 885163 | eBay
Engine model 3.0GSP-A service manual is Volvo part number 7743454
Setting Timing
The timing procedure for Delco EST system requires
shunting (shutting off) the electronic spark advance.
Follow the steps that apply to your specific model.
1. Install Timing Test Lead, Volvo Penta P/N
885163-6 A, into distributor, start engine until normal temperature is reached, then connect bare
lead to a 12-volt engine B+ source.
2. Direct beam of timing light onto timing grid.
Loosen distributor clamp, then turn distributor
slowly by hand until timing mark is set at the
appropriate timing figure. See Ignition Timing
Advance on page 64. Recheck timing mark;
reset if necessary. Tighten clamp bolt.
3. Remove 12v lead, Stop engine. Remove adaptor plug.
Volvo 3.0 Ignition Timing Advance Chart: 600 RPM is 8*, 1000 is 13*, 1500 is 15*, 2000 is 17*, 2500 is 18*, 3000 is 19*, 3500 is 20*, 4000 is 20*, 4600 is 21*.