Both those suppliers are good, very service minded.
There are another supplier I have use and it is Outboardpartsdotcom.
I am in Sweden Europe but no problem to buy parts from these suppliers.
They ship almost over the whole world.
I would install a separately battery for AUX devise such as fish finder and connect a voltage-sensitive differential relay.
The relay closes when the voltage reach about 13,5-14 Volt and you will not drain the starter battery for the engine by the AUX devises.
I am not super familier with the OMCs but they should actually be similar to Chrysler/Force with in the charging system.
16 Volt is not alarming high and the regulator should start to regulate at about 16 V.
Is 16 V at WOT or at 1000-1200 RPM?
Generally the alternator start to charge at about...
I do not trust the Chinese aftermarket parts.
If aftermarket use good brands such as Sierra, CDI Electronics otherwise OEM.
Used parts can be a challenge.
Have you checked the compression by your self or it is information from pre owner?
Have you checked the timing by your self ?
How have you stated you have spark at all three cylinders?
Do as topgun3690 and racerone says.
Clean the carbs and put a clear inline filter between the fuel pump and the...
Change both coils, not only one of them!!!
They are cheap and the one you do not change will fail soon.
BTW. When you check with your VOM for resistance, the VOM put out the battery voltage the VOM is supplied with.
Maybe 4.5, 6 or 9 Volt depending on brand.
My opinion about what have gone wrong is!!
If it was rebored, is it rebored to right spec.?
Has he checked the ring gap?
What mixture have you run at the break in period?
How has the break in been done?
Speed, load, RPM?
Do you have plug connectors to the CDI boxes or a terminal strip?
If plug connectors check the connectors for corrosion or oxide at the pins and sleeves.
If terminal stripe check the lugs for bad connection, especially under the heat shrink tubes.
That was a common issue for these ignition systems.
Good news. yes I agree with jerryjerry.
It is almost the best way to go with starters to restore them.
They with last forever with good maintenance.
Cleaning, change springs and brushes and sometimes change the bushings/bearings and they last forever.
That is the culprit or one of it.
Regarding the prop what size do you have right now?
4000 RPM at WOT is about 800-1200 RPM low
Going down 1 in in pitch would rise the RPM about 200.
You test them separate and do it with them disconnected and connected to the terminal block or connector plugs.
Checking with them connected give you answer if they put out right voltage when under load (CDI box).
Do as Flyingscott suggest, pull the LU and check water tube and impeller housing.
I am not really familier with the 70Hp, but there must be a pee hole or a idle relief hole at the back of the leg.
Does water exit from one of those?
There might be couple of brands out there but they are simply the same.
A DVA adapter contains as I said before a capacitor a diod and a resistor.
The purpose of it is to rectifie the AC voltage to DC voltage and store it in a capacitor.
Then you are able to read the peak voltage from the stator...
