Best way to verify ign timing
 

Last season I put a timing light on my engs for the first time since I got the boat.
Starboard eng was reading unusually high at abt 42 degs at idle and would adv to abt 45 degs at 3k rpm.
Pulled the outboard plugs and didn't see any signs of detonation.(static compression is at 10.25. 93 oct only)
Found rust in the MSD dist. Cleaned it out and installed adv kit. Mech adv works good now.
I set the timing the normal way so I was all in at 3k rpm with 34 degs total adv.
Went for a test drive and found my top speed had dropped by 7-8 mph.
Starting to think maybe the damper has slipped.
I was thinking about buying a degree wheel an a piston stop to verify if the damper had slipped or not. but not sure how well it would work out with such a tight bilge.
My back up plan is to swap dampers between the engs, but that's not much fun either.
Question is: Is there an easier way to verify if the damper has slipped?

EFi or carb ? Please say carb. :)

Go get an anti-fouler from the auto parts store they screw into plug hole and plug goes into them. (They are also good for getting cars past emissions when cat converter is going bad) tap a thread in the small hole in anti fouler and screw a bolt about an inch long into thread. You can also drive the center out of a plug and use that, but I think more work. You now have a piston stop. Install in cyl 1 with balancer timing mark mebbe 30 degrees from tdc. Put a wrench on balancer turn crank till piston hits stop. Mark balancer at tdc mark on timing cover. Reverse crank till piston hits stop again. Mark balancer again. Marks should exactly straddle orig tdc mark. If not, halfway point between marks is tdc.

Still running some old crappy Holleys (4010s). Thinking vacuum?

Good idea using an anti-fouler. Trying to avoid pulling the plugs if possible. The inboard 4 are just too much fun..

You could use 6 instead of 1 for tdc on the starboard engine.

the keyway lines up with TDC mark in most cases

When you changed total timing from 45 to 34 degrees,,thats a lot,, you lost horsepower, and speed, set it to 36 degrees total and go run it, will most likely pickup a mph or 2.

He shouldn't see much diff between 36 and 34. I think he was nowhere near 45 when light said so. Woulda been pinging like crazy and running hot. I think he was close then and now 34 is really in the 20's.

Wouldnt it be an absolute pig getting on plane if it was in the 20's?

are you using a digital timing light?

We dunno whether he was timed right at 45 or what. I think it would be better in the 20's than in the 40's. I just checked one of my balancers. It is about 20 to 30 degrees from keyway.