Which tach adapter did you use there are a couple different ones from msd I'm just running a carbed motor ?

I believe it is the 8920. You certainly could call their tech

Sorry, it was a long time ago. However, I just googled MSD tach adapter. The one I used was definitely the physical shape of the 8920. So, I am pretty certain that was it. Again, call them!

If you can, I would ditch the MSD system completely, and use a Merc TB-IV distributor and a V6-14 module. I'll be that's where some of your top-end running problems are coming into play.

The Merc TB-IV is just about bulletproof and very simple.

You have to be kidding with that statement!

I doubt he's kidding.

MSD has a well deserved reputation for being problematic and the thunderbolt has a track record of being relatively problem free.

Please. First of all he says "I'll bet that's where some of your top-end running problems are coming into play". Where and when was that ever mentioned. And the MSD being problematic. Seriously, many, many thousands have been sold and their defect rate is probably better than most. Parts break.......auto parts, coffee makers, whatever. Truthfully, I put the MSD system on my present boat because the thunderbolt distributor and V6 module were acting up. I'm not bad mouthing the Mercury part.

Yes, seriously.
I've had two boxes quit and a distributor that corroded beyond operation.
No thanks!

Well, I'm sorry to hear that, but I'm not sure that makes for a bad product overall. Here's 2 of us talking. You had a bad experience. I have had a good experience on 2 boats. As I said I had 2 systems on my first boat that were trouble free for the 5 or 6 years before I sold it. The 2 systems on my current boat have been fine for that many years as well. What can I say?

Curious in this application what the msd box does that a thunderbolt iv cant? Rev limiter?
A few years back I went with a pertronix distributor because i needed more initial timing without more total as well as the total coming in quicker and have been very happy with it. But I've never had an issue with the thunderbolt and have used v6 modules where more initial is needed.