Suzuki DF70 power loss

[5.5 mtr]

Hi all,
I have a 5.5mtr with a suzuki DF70 with no power. On the drive she runs absolutely fine revs to the limiter in gear in a test tank.
But in the water it won't rev past 1100RPM it's like trying to pull away in 3th gear in a car the engine bogs down and just will not pick-up.
I have brought a diagnostic program and it shows no faults at all and I have been through all the normal tests,compression,fuel pressure and plugs.
I am now at a loss of ideas and power any clues as to what the problem might be would be much appreciated.

[Pikey Dave]

Originally Posted by 5.5 mtr

Hi all,

I have a 5.5mtr with a suzuki DF70 with no power. On the drive she runs absolutely fine revs to the limiter in gear in a test tank.

But in the water it won't rev past 1100RPM it's like trying to pull away in 3th gear in a car the engine bogs down and just will not pick-up.

I have brought a diagnostic program and it shows no faults at all and I have been through all the normal tests,compression,fuel pressure and plugs.

I am now at a loss of ideas and power any clues as to what the problem might be would be much appreciated.

Carbed or EFI?
When you say you’ve run it in gear to the limiter in a test tank, is that with the prop on? Have you checked your hull isn’t full of water? 70 hp is on the small side for a 5.5m. Is this a new purchase or have you owned the boat for a while, if so, has it suddenly changed behaviour or has it always struggled?

[5.5 mtr]

Hi it is EFI and the Hull is definitely not full of water and the pro was on thanks and the prop on

[Pikey Dave]

Originally Posted by 5.5 mtr

Hi it is EFI and the Hull is definitely not full of water and the pro was on thanks and the prop on

Has the problem suddenly appeared? What’s the history of the problem? I.e. have you just acquired the boat & it’s been like it since you’ve had it, or has it been fine in the past & the problem has suddenly developed. You’re going to have to give as much info as you can if we’re going to be of any help.

[5.5 mtr]

Hi so I purchased the rib at the end of the summer 2019 it had been used by the previous owner all that year I have seen videos of it with this engine running fine and getting up on the plane with 4 people on board. When I purchased it she was a bit neglected faded tubes gauges not working wiring a mess so I spent time and gave her a good clean up and so on. The first time I took her out we got just out the harbour on around half revs not on the plane and as I pushed to WOT the revs went up she started to lift up on to the plane and the throttle broke in side the control leaver we limped back into the harbour.
I then replaced the control unit with new then th good old covid came along and she sat for about a year and I now have this loss of power issue which I thought was me not setting up the controls properly but I have checked over and over and can't see any problems the butterfly in the throttle body is fully open at max on the controller and it go's in and out of gears fine. It's also had a full service I've even tried it on a remote fuel tank in case the in board tanks fuel has gone off.

[TimB]

Have you a water separator fuel filter on transom, that has a clear bottom half that can be unscrewed. If so check the rubber gasket as I had one split, let water in and I had a problem similar to what you are describing on a 60 efi

[5.5 mtr]

I have but that has been replaced it new filter and seals

[Pikey Dave]

Originally Posted by 5.5 mtr

I have but that has been replaced it new filter and seals

So it runs ok in the tank with the prop, in gear. Did you run it at WOT in the tank? What was the max rpm? (Must be a big tank!) when you replaced the control unit, have you connected the cables the right way round? Without knowing the specifics of the control box, you may have connected the throttle cable incorrectly so that when you go into forward gear, you’re getting reverse throttle. Just a guess.

[Orwell boy]

Originally Posted by 5.5 mtr

Hi all,
I have a 5.5mtr with a suzuki DF70 with no power. On the drive she runs absolutely fine revs to the limiter in gear in a test tank.
But in the water it won't rev past 1100RPM it's like trying to pull away in 3th gear in a car the engine bogs down and just will not pick-up.
I have brought a diagnostic program and it shows no faults at all and I have been through all the normal tests,compression,fuel pressure and plugs.
I am now at a loss of ideas and power any clues as to what the problem might be would be much appreciated.

Your not trying to turn a 23" pitch prop with four people on board ???

[matata]

Im guessing it has a VST tank(Its like a fuel resivoir tank) I d drain that into a clean jar and have a look....Is it clear ,clean..let it settle for an hour...any difference or layers....Also the fuel rail into the injectors has a rail that distributes the fuel into the injectors...It may have a schraeder valve on it that you can measure the fuel pressure before going to the injectors.. I'd measure this pressure as the engines running under load. This will more or less tell you how the fuel system is fairing up. Next take out the plugs and see if they are an even colour of grey/brown...Any of the plugs look different...dry or very wet?
You haven't mentioned a miss fire so thats good and you've done a compression check .

Keep us posted ...Nik