Volvo KAD 42s

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Keithleask

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Hi, seem to have a problem with my KAD 42s on 39ft sunseeker, bought the boat and had sea trials where the starboard engine overheated, changed the impeller which seems to have cured that.Boat performed great on the re arranged sea trial, 24 knots from memory. But, took the boat out last week and when i got it up on to the plane as i pushed the throttles forward the engines slowed down it came off the plane and it just feels like a massive flat spot like you get on a car engine. Tried it several times and each time it would get to 17/18/19 knots then lose power, throttle back and give it a few seconds and the same again. The boat was out of the water in July and the bottom was spotless so no crud, the outdrives were serviced in March, the bellows changed etc, and no crud on the props, so am thinking fuel problem, blocked filters or possible air filter problems, any ideas from any of you experienced hands on guys out there would be really helpful, thanks,
Keith
 
Keithleask said:
Hi, seem to have a problem with my KAD 42s on 39ft sunseeker, bought the boat and had sea trials where the starboard engine overheated, changed the impeller which seems to have cured that.Boat performed great on the re arranged sea trial, 24 knots from memory. But, took the boat out last week and when i got it up on to the plane as i pushed the throttles forward the engines slowed down it came off the plane and it just feels like a massive flat spot like you get on a car engine. Tried it several times and each time it would get to 17/18/19 knots then lose power, throttle back and give it a few seconds and the same again. The boat was out of the water in July and the bottom was spotless so no crud, the outdrives were serviced in March, the bellows changed etc, and no crud on the props, so am thinking fuel problem, blocked filters or possible air filter problems, any ideas from any of you experienced hands on guys out there would be really helpful, thanks,
Keith
Click to expand...

This isn't the one from shamrock quay is it?
 
What model sunseeker is it? You should be getting more than 24 knots with kad 42's.
The surging could be a problem with the superchargers cutting in and out.

Rob
 
Throttling back then going again sounds like fuel starvation , once the chargers are in they stay in until the Turks take over, f there is insufficient fuel the revs will drop along with the boost, hence the chargers cut in again relaying the cycle.

A dirty hull would not produce that effect , so its back to basics , filter check or renew.
 
Rob hi it's a Martinique 1994 , 650 hours on the engines, could be right with superchargers cutting in and out that's what it feels like and if I leave the throttles pushed forward it just slows right down,
 
Paul hi, thanks for that , I will take a look tomorrow , anything in particular to trace, or clear ? Just the main fuel filters would it be do you think?
Many thanks o
 
Hi Keith,

I had a 1992 Martinique with AD41's @ 200 HP. It ran close to 30 knots so I would expect a boat with kad42's to do more.

Interesting comment about the supercharges volvopaul. I think I need to check my filters too in that case. End of season blast brought some surging.
Really felt like the chargers cutting out around 3000 revs before the turbo's were ready to take over.

Keith, I would follow volvopauls advice above mine. He's the expert.

Good luck

Rob
 
Depending on year model you may have the old style Lucas cav filters, or some nice racors if later model.

The racors are a torpedo looking upright filter with a t handle on the top, the cav type has an element sandwiched between the head and alloy bowl at the bottom.
 
Rob, hi thanks for the advice, I will pay attention to the master, volvopaul as it seems he is the master in all things volvo, will let you know how I get on, thanks,
Keith
 
Paul,hi ok then , thanks again ! if they are the old style Lucas/ cav filters, which I think they probably are as I do not recall seeing anything like the rancor torpedo shape type with t handles on the top, is it straightforward to replace the cav type with the racor ones? Seems like it is better to change them even if it might not be the problem but upgrading would seem a more sensible thing long term anyway ? Your help is really appreciated,
Keith
 
Hi. My money's on the turbos. Do the revs drop off as soon as you hear the superchargers cutting out?
Cleaning the props usually stops it happening for a short time. Remove the exhaust elbows, see if the turbo spins, and check the clearance between the turbo blades. Any more than 2mm and they are shot.
 
I'm with Paul and fuel starvation. I had similar a couple of years ago. For some reason the boat had fine wire gauze over the fuel pickups in the tank and one was getting blocked. enough fuel getting through until the turbo cut then the rev's would die

Fuel filters are easy to change and inexpensive so would definitely start there
 
Hi, really not sure if it can be the turbos, the superchargers scream in but it never gets up to the changeover for the turbos, am leaning to most guys opinions here with the fuel filters, gam trying to find out which racor ones will fit as they seem to be a much better piece of kit,
Thanks,
Keith
 
Kevin hi and thanks , must admit leaning heavily to the filters, am going to take them off tomorrow and see if I can source some new replacement racor Ones, will keep you posted thanks,
Keith
 
Just change what you have now, new is better than old if there blocked, if you do have the Lucas ones they were fitted from new so will do the job as long as the tanks are not sludges up. If they are then the problem will return quickly so you need to clean the tanks out as even a nice new racor won't last for long. Try blowing down the pipe from the tank to check for partial blockage. Also there may be a gauze filter in the lift pumps if they are the type with the screw top.
 
Last edited:
Keithleask said:
Hi, really not sure if it can be the turbos, the superchargers scream in but it never gets up to the changeover for the turbos, am leaning to most guys opinions here with the fuel filters, gam trying to find out which racor ones will fit as they seem to be a much better piece of kit,
Thanks,
Keith
Click to expand...

Not sure what you mean by "the superchargers scream in" but that's not how I would describe it when they engage so if they really do "scream" you may also have an issue with the drive belts not being tight enough, ie slipping and making a screaming noise as they slip on the pulleys.
 
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