More EFI to Carb Questions
 

My question has to do with the wiring harness. When we switch from EFI to carb, is it possible to get a used merc harness that will plug into the system like the efi harness does? It is a 2000 Gen VI 454 MAG MPI with a MEFI 3 computer.

That way I won't have to cut up the EFI harness and can sell the manifold/ecm/and harness all as a package. I figure the best money to be had is that way.

That's exactly what I've done. The wires are all still in the loom but the still active feed wires for the gauges etc will hook up. I'm running a carb with an MSD ignition so I'll keep that out of the harness but all I did was grab a used (and fused linked) engine harness (female end) off ebay for cheap to link into.
Good luck! (I hate wiring...)

Curious, why go from EFI to carb?

A couple of reasons. First, the 454 MAG MPI intake is pretty limiting, and we could tell even on the dyno that we ran out of manifold at 5200 rpm. We need to go to a Single plane intake to let it breathe like it really needs to.

Secondly, a carb will be easier to tune in the boat. I discussed with my engine guy the option of going to a single plane efi setup like the Victor Jr or similar. To do that, we would have to pull the engine, put it back on the dyno and build a new program from scratch. This would be many hours on the dyno and a lot more money than switching to a carb in the boat for what will be very similar results.

It boils down to how much more money I want to put into it, and at this point I've already got way more in it than I'll ever see out of it. The overall value of the boat is not such that I can keep pouring money into it. As it sits now, with everything I've done to it, I've got well over $50k in a boat I probably couldn't sell for $30k. I don't regret the money I've spent at all, and I've certainly enjoyed it. At some point though, common sense has to rule!

don't think a victor jr is a good choice for a boat....moves the rpm band way to high to work well at all, a performer air gap will work much better in a boat..Rob

Hi Rise single plane manifolds are king on most 500hp+ marine engines I've seen. Heck, even the merc HP500 came with a Dart single plane. The Dart manifold is what I've picked up for mine.

Don't hack up the EFI harness.
You can buy a new harness from CP Perf. for about $200.