TAMD41Bs again...one for spannerman???

[PAULSTEWART]

Weather so good yesterday went for first trip of the year up to Bucklers Hard for lunch - or so I thought as pub was shut for a refurb /forums/images/graemlins/frown.gif
Got near to the entrance to Beaulieu, and slowed for sailing boat close by. When throttled up again, starboard engine would only go up to 3,000rpm max, and then started to fluctuate between 2,000 & 3,000 all by itself. Was like a 17 yr old in his fiesta at the lights blipping the throttle for best part of an hour.
Did this all the way back to Portsmouth, and going against the tide couldn't get on the plane (not helped by a years growth on me bum!) so was doing haydns trick of making everything behind disappear in a large thick black cloud of soot!
When back in harbour, put engine in neutral, and it ticks over fine and revs perfectly all the way up to 4200.
It's steady any where in the rev range and no smoke at all.

I won't say what my thoughts are, as want to pick your brains as to causes before I waste money on guesswork...

 

[DaveSteward]

First thing for me would be fuel filters. Sounds like you may have a partially blocked filter.

David

 

[DAKA]

Agree, filters have to be the first to change.

But surge in power is a little odd.
Sea trial

full throttle port, and tick over stb, then full starb

if boat leaps onto plane before drops off then chances are fuel filter and you can narrow it down to which is the poor side.

If there is also a slight surge at slow speed I would turn my attention to the flexible fuel lines, perhaps there is a slight crack in the pipe that is letting air in which would replicate the symptoms described.

Also Check fuel lines for leaks by starting the engine, not letting it get hot to evaporate the leaked fuel.

I would also ask and wait for spannermans/cols advice .

 

[strakeryrius]

I had a similar problem where stbd engine wouldn't sit at cruising revs - they kept dying back to 2500 then surging up to 2800 again just on that engine. Turned out to be a problem with the turbo not producing enough boost to get the supercharger to cut out properly.

 

[volvopaul]

Sounds like fuel starvation, how long is it since the prefilters were changed, air maybe getting in, check all pipework and flexi pipes to engines, also check fuel taps, have you had any winter work carried out, maybe some else has upset pipes or taps, filters etc.

Black smoke is unburnt fuel, but that must have been coming from the good engine?

There is a gauze filter in the lift pump, check that as well.

If all else fails pm me.

 

[spannerman]

Everyones beaten me to it, so I concur, check/change the filters and check for airleaks, had surging on a 42 once only at higher rpm's, it was air leaking in at the tank connection. If in doubt make up a clear section with hose between the prefilter and fuel pump. Although I have had a couple of fuel pumps leak air into the system, but usually then the engine stops.
Also check the turbo spins freely.

 

[PAULSTEWART]

Thanks guys for all your advice. Will change filters when down next. Hope you're right, if so, not to expensive a repair!
Fingers crossed...