I have the Holley HP on my 383. I'd put that Holley HP on my 350 but all the sensors are different from the 350. Kind of like first generation GM sensors versus 2nd generation GM sensors.

Ok, I'm a little lost. I need more data on this situation.

What boat, what prop and drive, what motor, which MEFI unit, what size injector, what mods to the motor, what rpm did you do the 80 mile run at? With some more concrete data I might be able to offer more advice.

I would not be too hasty in ditching even a MEFI 1. They are simple and robust.

21' custom weld storm. 350 running on mefi 1. 2.9kw impeller. No mods. Not sure on injector sizes. Mostly cruising rpm 3200-3400 for the 80 mile jaunt.

Ok, so assuming there are no modifications I've got a better picture of your setup.

Jet boat in a 3500 lb 8 foot beam aluminum hull boat. Jet boats like gas. Did this 'high' fuel consumption always occur with this motor and hull? Or is it something new? An equivalently equipped boat with a Bravo drive would yeild about 2.2-2.5 mpg at the rpm you cruise at. You were getting about 1.3 mpg. Being that its a jet boat that is not terribly surprising but I'm not sure it should be that low. My best guess is somewhere around 2 mpg in your setup.

Does the black smoke on start up occur continuously even after warmed up?

Does it occur at cruise rpm?

What do the plugs look like?

When the problem occurred was on that first long trip with THIS motor. Other than that I had 260+ hrs on my 383 that would go much further on the same amount of fuel.
I'm just basing my fuel consumption on other 350s in known hulls like mine getting far better fuel economy with 350s.
The heavy black smoke goes away as it warms up. I'm assuming this is warmup enrichment. Running down the river the smoke is disappated from swirling winds. I can smell fuel though.
I appreciate you trying to help me out.
When marine power had my ECU, I was asking for them to check on a updated program. If there was an update to please load the latest program onto the ECU. It was months of trying to get my ECU back as the guy that had it would not answer my phone calls. I finally got it back but it is unknown if he did anything to it.

Why did Marine Power have your ECU? To solve the fuel issue or did the fuel issue happen after you got the ECU back?

Either way it sounds like its a crap shoot on what is actually on your ECU. I know this is water under the bridge so to speak but I've never seen it necessary to get the 'latest' update on an ECU, particularly an old MEFI. The original tune is usually sufficient and parameters limited.

Did you happen to change out the MAP sensor? If so did you put a 1 bar MAP sensor back in or a different one?

Thanks for your input. I figured it was running an old outdated file. Probably the original one as far as I know.
If I remember correctly the fuel issue came later. However, I'm not quite sure if it existed before MP had it. I did not have the motor very long (hrs) before I sent the ECU to them. Like I said the guy from MP kind of went awall for a bit. I got worried enough to start making noise. For all I know he screwed with it for getting in trouble. That's just a wild wild theory that has no basis BTW.
I have not switched the MAP sensor out. I suppose it could have been done before I bought the motor.
I'd drop my Holley HP in there in a minute if I had the wiring harness for it. Hell I live that idea.

Have the injectors been flow tested and cleaned.

Injectors have not been flowed.

I ran a sweep on the TPS and the voltage was good. That was awhile back.