It'll also burn up the exhaust valves and cook the cylinder walls and rings. 24 degrees total is great way to ruin your engine.

Set it to 32-34 total. If it audibly pings on regular fuel at 34 degrees, back it off.

Honestly, I believe that you're about to go way over your head with this thing. The stock Thunderbolt ignition with the 24 degree module should work fine with your engine. If it's messing up, either a component has gone bad (and you need to properly troubleshoot it using Mercury's diagnostic procedures) or you have a bad ground, these things are basically bulletproof in their operation especially the version you have.

If you are bound and determined to get rid of the Mercurry system, buy a GM Voyager Marine ignition kit. It uses a Delco small cap distributor, and comes with everything needed to install it. It has a preprogrammed module that works well on a stock or mild perf big block. Install it, set the timing at 32 degrees at 3k rpm and be done with it. Cost is about $350.

But I seriously doubt that there is anything wrong with your TB-IV. Sorry if I sound so militant on this point, but I've worked on a lot of these systems; they really are the last thing to go bad, and engineering something "better" usually ends up really messing up a good engine.

I have followed the little trouble shooting guide. It has power where it is supposed to. Every ground has been cleaned. The ony thing left I have to suspect is the v8 24 module. The price of a new one is outrageous. I see where Mr gary offered to let me try his for troubleshooting. That is awful nice of him and I appreciate it but if that does help then that means I have to buy one. Hei distributors work every day in vehicles. Worst case in a year if it farts out, another $50 and we go again.

1) I totally agree with TomZ
2) Modules can be had here for $100 easily, this is where I got my spare, (different curve & advance)
3) I believe when you are done chasing your tail on the ignition you will be back in the carb and fix the problem.

A carburetor will not cause a direct misfire on 3 cylinders under 1000rpm then mysteriously disappear above 1000 rpm. This is 100% a firing issue. The carburetor bowls are holding fuel. Every gasket, accelerator pump, power valve, needle and seat are new. I've buit enough carburetors to know that it is not a carburetor problem.

I am not saying the tb iv is a bad thing. I'm just saying it is apparently bad on mine and the price of a module is the price of 2 heI distributors.

Now I am confused. Post #111, idle to 3,200 OK. Post #149, OK until you hit secondaries (2,500) then busting up. Now Post # 214 running on 5 cylinders <1,000 then clears up.

Try Gary's module. If it works, you'll know that's the issue. If not, then the ignition isn't the problem. All it'll cost you is the shipping.

Guys sell this stuff in the Swap Shop all the time. If you post something in the wanted section, I'm sure you'll get some quick hits.

And don't discount the carb issue. I've witnessed plenty that have acted relatively the same way. Just saying. Do you have another carburetor to try just to see how she idles?

Heck, you pay round trip shipping and I can send you module (V8-20), distributor w/module, wires, and coil. Sorry I sold my last Q-jet I was keeping for troubleshooting purposes.

It has progressively gotten worse gary. Earlier in the thread (2 weeks ago) it was just in the secondarys. As time has gone on (3 water tests) it has gotten worse. I can watch the carburetor spraying fuel. I am more than confident it is not a fuel issue. It is something in the ignition system that is either breaking down or is failing under a load requiring more fire.

It is more than likely the module. That I all I can see it to be by the little procedue mercury has. I might look at the sea ray and see what modules it has if it has any.

Just a stray thought, how are the batteries and charging system. Not just voltage but load test.