yamaha 200hp Engine power loss

 Hi All,

I have an issue with my 200hp Saltwater series2 2 stroke engine. 

On 'flat' water there is no issue and the motor pushes along my tub nicely. but particularly in a following sea but also 'big' seas, coming down to the trough the motor cuts revs. sometimes enough that I disengage the motor then put back in gear and power on. It does not stall and apart from this issue, it is extremely reliable. 

I have read the other topics similar to my issue on the forum but my issue seems slightly different and I wanted a little more precise information.

I have had a boat mechanic give it a full service. There is no micro switch for the gear engage selector. I have changed all fuel lines and filters and manual pump. I have checked the high pressure pump for particulates, and still the issue persists. It does this with a full tank or half and even one quarter full tank. 

Thanks for any help you can offer.

Jackalchub's picture

Posts: 598

Date Joined: 10/03/12

 Sounds simple, but I’d be

Sun, 2018-01-21 12:27

 Sounds simple, but I’d be checking the connections/lug faces on your isolator and battery.. If you lose battery power intermittently you are running off charging voltage only - which may not be enough to run fuel pumps, etc.. I have seen this before. Isolators are generally in a position where they can cop salt, etc.. worth a look anyway.. An indicator might be that your charging voltage is slightly down on dash. Personally, I’d solder the cables into the lugs, rather than crimp. 


Hope this helps 

Adam Gallash's picture

Posts: 15626

Date Joined: 29/11/05

Had similar

Sun, 2018-01-21 19:56

 Had very similar prob before and one of the battery terms had come loose. Was fine in calm but when it was rough and the boat got a bump it would cause the connection to be an issue and drop revs / cut out.

Hopefully its that simple.


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Sea Hunter's picture

Posts: 148

Date Joined: 04/07/13

Give that a go

Mon, 2018-01-22 16:47

 I wondered this too, but then thought that it probably wouldnt matter because the engine generator should be enough to run the engine. but that may be flawed thinking of course. This is a great spot to start thanks 

Posts: 274

Date Joined: 08/10/13

 Clasic sign of the fuel tank

Sun, 2018-01-21 14:28

 Clasic sign of the fuel tank vent not working correctly.  Getting a vapour lock intermitantly.  Run it off a portable tank to see if it is the problem.

Sea Hunter's picture

Posts: 148

Date Joined: 04/07/13


Mon, 2018-01-22 16:48

 I did check this but I will definitely be checking again as it certinly cant hurt

NORUN NOFUN's picture

Posts: 1023

Date Joined: 15/08/11

I doubt this is the answer,

Sun, 2018-01-21 20:39

I doubt this is the answer, but had a similar issue on my old tinnie with a 2 banger.

The fuel was stale and had formed a jelly substance in the fuel bowl of the carby.

Was fine when flat, but trying to get up on the plane the jelly would move in the bowl as the boat was on a bigger angle and would close off the float and the engine would get no fuel.

It's the intermittent faults that are always the hardest to diagnose.

Good luck.

Sea Hunter's picture

Posts: 148

Date Joined: 04/07/13

I hope not

Mon, 2018-01-22 16:50

 I have changed all lines and filters and manual pump, so i am hoping that the geletinous fuel is not the problem

Posts: 5981

Date Joined: 17/06/10

Just looking outside the box

Sun, 2018-01-21 21:55

You say that with a following sea, and coming down into the trough on big sea it appears that the motor drops revs.

Could this be caused by coming down into the trough the motor/boat is actually surfing to some degree, if so you will notice that the motor increases revs as the amount of energy to push the boat is greatly reduced, hence engine is not working as hard revs increase.

When coming out of trough engine has to work harder and revs will decree.

You can check this out very easy watch the tacko when coming down a wave a in a following sea ( not a big wave you shouldn't surf down any wave if you can help it) you will see via tacko increase in revs when you are in trough revs will decrees as the motor gets the increased load again.

Just a thought outside the motor box

Sea Hunter's picture

Posts: 148

Date Joined: 04/07/13

problem solved

Fri, 2018-06-08 17:10

 Hi all who are interested.

i checked everything and serviced everything and still had the motor cutting out at the bottom of the trough, both going into the wave and coming over the back of the wave and hitting the trough. i finally found a mechanic that was willing to chat about the issue. he told me before he would bother coming to have a look to change anything that i had 'modified'. The only modifications i had made was changing the prop in an effort to gain higher top end speed. I started out with a 17 pitch and changed it to 19. This gave me about 6 knots more speed at all stages through the rev range. I then put a 23 pitch which gave me another 3-4 knota top end and cruising. (Preamble over).

After speaking to him I changed the prop back to the 19 pitch. I tentativley took it out in calm weather and had no issues. I then took it out during the last storm with huge seas and again had no issues. My latest test was in relatively calm seas but with a reasonable swell and had no issues. 


My theory is: with the high pitch prop the engine was maxing out on the torque. I was not able to achieve max (WOT) revs. Then as I hit a bit more load (at the bottom of the wave or the trough) it overloaded the torque on the motor. Sort of like when the prop is wrapped in rope it just stalls. 

Posts: 812

Date Joined: 09/10/06

 You must of be lugging that

Sat, 2018-06-09 09:38

 You must of be lugging that motor trying to turn a 23.  It's a must to be in the optimum RPM range at WOT carrying your normal load. Something that gets overlooked for top end speed.

Sea Hunter's picture

Posts: 148

Date Joined: 04/07/13

too true

Sat, 2018-06-09 13:08

 definitely overpropped. I didnt realise it would have that effect on the engine. Lesson learned.

ranmar850's picture

Posts: 2702

Date Joined: 12/08/12

Sounds like you were massively over-propped

Sat, 2018-06-09 10:38

 Top speed isn't everything. Boats don't have multiple gear ratios to work off, and that prop has to do it at all speeds. Going from a 19 to a 23 is a massive increase, unless it was extremely underpropped to start. 

Sea Hunter's picture

Posts: 148

Date Joined: 04/07/13


Sat, 2018-06-09 13:44

 So now i have a 23 prop for sale