Hunter, As I remember, you have your throttle marked for secondary opening. If the sputter is truly related to secondary's opening I'd look at the carb closely especially on that secondary side. Is it firing thru the intake or exhaust when it happens? Can you drive through it? You'll get it and another 5 days of warm to boot.

Yes sir I marked the throttle. It got worse as the day went on. Almost certain it is plugs and wires. Decided to do it all and get rid of the thunderbolt. Ordered an hei distributor, 8mm wires, and got some new plugs coming.

Been looking at doing a fitech fuel injection set up. Only real issue would be the 02 sensor. The engine builder said i should be able to remove the intake, drill and tap the heat cross over and put the o2 sensor in that. Anyone ever done that?

Scratch that great plan. After researching some hot rod forums it appears the air is rather stagnant so that obviously isnt good for 02 sensor readings.

find another builder................

I'm speaking to the man that built the engine that is in the boat. It has approximately 60 hours on it now. Hope not to need an engine for a few years. I am just looking for suggestions on how to mount an 02 sensor so I can do a tbi set up and get rid of the carb. I have a theory of how to do it but don't really want to go the route I had in mind.

You can buy a spacer that goes between the manifold and riser that has an 02 bung in it. Although I don't know how long it will live in a closed loop system. Efi is nice but really a good carb should be trouble free.

http://wagsengineering.com/products/...sensor-spacer/

The darn fuel these days us just terrible on them though. Especially if it sets for more than a month or two.

The carbureted set up is simple. It seems like you're trying to go the route of the TBi set up to deal with your secondary tip-in issues.

I'm not sure of which ignition you were originally running, but if it's the Merc stuff, then you're wasting money on replacing a very tried and true, reliable ignition system. A cap and rotor, good wires, and spark plugs should be all that's needed.

Your engine seems to be fairly close to being like a stock Mag engine; I wouldn't go changing a bunch of stuff. A good tuneup, and some adjusting of the carburetor should get you going in the right direction. If the stock stuff has been replaced with something afternarket/automotive, get the stock stuff back. I have a good Thunderbolt IV set-up with a 24 degree module, new cap and rotor, and wires, if you're interested.

I want tbi because the carburetor will never be as crisp of throttle response. The tbi will not flood, will not over fuel and foul spark plugs, and it will crank well when cold. It has the thunderbolt on it now. Your correct that a simple tune up would correct the week fire issue I have now. But I honestly don't want to waste my time with 1972 ignition technology. Hei will use 1 wire. It cost less for a new lifetime warranty hei dizzy with 8mm taylor wires than a "marine" cap and wires from my local mercury dealer.
Not trying to be contrary to all of the good information you guys are giving, just trying to upgrade rather than beat a dead horse. The carb is doing fine for now. Just want to replace it eventually.