Volvo Kad 32 performance problem

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SJT671

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Hello, Could anyone please comment on the following. I have a Targa 30 with twin volvo kAD 32 170hp diesel engines. When powering up she gets to approx 2600 2800 revs then looses power, the stern drops back down and diesel is decanted out through the exhausts, power recovers she attempts to plane then repeats the scenario. This happens when there is a swell of say one to one and a half meters. On a flat sea she revs to 3500 and pulls 28knts. We have changed all filters and belts ,the supercharger clutches have been adjusted, hull and outdrives are clean. Any help greatly appreciated thanks for reading this post.
Steve.
 
Hi,

Has this always happened, or has it just started happening?

Do both engines do pretty much the same thing, or does one drop revs first, followed by the other?

Someone can correct me, but I thought T30's were propped with A7's to reach 38kts or thereabouts, not 28kts. 28kts at 3500rpm doesn't sound too good.

dv.
 
[ QUOTE ]
Someone can correct me, but I thought T30's were propped with A7's to reach 38kts or thereabouts, not 28kts. 28kts at 3500rpm doesn't sound too good.

[/ QUOTE ]

I'm of the same opinion. If bot, legs & props are clean & engine runs to 3500 it must be incorrectly propped. Although if it was underpropped ie only pulling 28Kts, I'd have thought the engines would be screaming on the limiter.
 
Have you checked/replaced the main belt from the crankpulley up to the water pump pulley, I had this problem last week on a boat and they had done all the filters etc but no improvement.
What folks don't realise is that this belt does all the work, i.e. drives circulation pump, and via two more belts the alternator, and compressor when it cuts in, any slack and it will slip when working hard, which then means the compressor isn't working to max and your alternator is slipping so you get false tacho readings as these come from the alternator, and this then effects the relay controlling the compressor cut in/cut out speed as this is driven by rpm which also gets its signal from the alternator.
I think this is the root of your problem.
 
Once again many thanks for your time and comment, I'll pass the info on and update once investigated. We replaced all the belts but the port side alternator needed tightening, maybe the mainbelt needs the same??. Thanks.
Steve
 
Although I agree with Spannerman I cannot get around the fact that the problem is above the range of the supercharger. The cut in RPM is 1700 and the cut off is 2600 so at the speeds you are talking about the super charger is not working, it is all on the turbo's. It does point towards the way your engines have been set up as they both follow the same pattern. Although I have stated about the super chargers I notice in your question that the super charger clutches have been adjusted - why?
The engines are not running to their full load RPM of 3900, can you rev them above your stated RPM with no load?
What is the condition of the fuel in the tank?
Sorry for all the questions but at the end of the day it is a common fault to both engines so chances are it is a really simple problem probably staring at you in the face, but we will all learn from it.
I hope this is of some help.

Steve
 
One more thing I agree with all other comments but the air inlet valve, the black plastic box inline with charger and air filter etc has to change over air direction when the charger cuts out, maybe one is stuck not letting air into turbo hence the black smoke, or politely put ( decantering) out the exhaust .
 
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