Slow acceleration, Black Smoke

Hi All,
Im having trouble with my engine spooling up to slowly,

It's a single Yanmar 4LHA STP , in a Judge Chesapeake 27

It takes 30 to 50 sec to get up on plane with a lot of black smoke,

runs fine at top end, WOT is 3400 with some smoke,

the injectors were bench tested and all 4 popped at 3,000 lb ,

the boost pressure at the intake manifold is low during acceleration with the gage needle bouncing from 0 to 10 psi,
at 3,400 rpm under way the boost pressure is 28 to 30 psi at the intake manifold,

I power washed and had the after cooler sonic cleaned twice , i can´t see through the tubes on the air side but I think its clean because I´m getting 28 - 30 lb of boost at WOT.

the turbo fins and bearing feel tight and spin freely and look ok some carbon build up, the turbo dump valve is free and seems to be working fine, I took it to Metro Fuel shop and they said it looked fine, within spec.

I changed the fuel filters and the air filter,

the fuel tank and lines look clean and are free flowing and the fuel is not at all cloudy.

the bottom of the boat isn't dirty,

The exhaust drops 14 inches from the mixing elbow and seems to be clear with a small amount of corrosion on the mixing elbow,

I have the same prop that I had before the problem,

It was a gradual not an abrupt change in the slower acceleration.

It has a Yanmar fuel pump delivering 20 lb to the injector pump, I measured it after the filters,

The Yanmar injector pump has a diaphram governor with an air line running to the intake manifold being adjusted by the boost pressure witch in turn regulates the amount of fuel delivered to the injectors, I think it's called an (aneroid)???

Has anyone had experience with these pumps ???????

Any help would be appreciated

Thanks Steve

you really think so ? after a turbo shop checked the specs and said its ok. the reason i dragged my feet is a new one is $3,000. thanks for your input.

The other things that happened were, the exhaust elbow snapped in half and blew exhaust into the engine compartment filling it with the exhaust fumes, the engine had a hard time running putting out a lot of black smoke until I figured out what happened and open the hatch, I had some wire to hold it together to make it back to port about 20 minutes of easy running . some of the foam air cleaner was sucked into the engine from the heat.

Several years after that I backed into a rock quite hard and bent the prop shaft and slightly bending the skagg, I had it repaired at Port Niantic Marine in Ct. with a new shaft, the prop was sent out and was ok, they also installed a new exhaust from the elbow to the transom, it also was cracked.
Thanks for your opinions
Steve

yes I can see the linkage of the wastegate while underway, how would I test that theory?

Ralph, It ran fine for two seasons after the carbon incident,
then it has gradually been getting worse, at first it was only once in a while, now it's a problem every time I accelerate.
BRyachts , my fuel system is mechanical but I could see how a bad sensor would mess things up.
thanks

It seems a defective waste gate would dump excessive pressure at higher RPM instead of low. No???

I've run the boat at 3000 to 3200 RPM for an hour and a half with no problems, it's hard to tell when I'm underway if there's much smoke at WOT.

When new the exhaust was fiberglassed into the transom (about a 4 foot section) with no flex coupler at the aft section, when I hit the rock it cracked , the floor was cut out to fiberglass a short flange onto the transom then a flexible boot and exhaust tube installed up to the riser, this is all new and as far as I can see inside it's clear.

I bought a boat used and always had black soot accumulate on the back of the transom, even after a half day on the water.

The boat is a 27 footer so i trailer it and the bottom is clean and its the same weight.

I may be able to get a pyrometer to measure the exhaust temp?

What would the nano gauge read turbo boot or exhaust ?

I was thinking of drilling a quarter inch tap on the turbo side of boost just before the after cooler, I have a gauge on the intake manifold, that would insure the air side of the aftercooler is clear.