tohatsu 2st 25hp

[tenga]

Hi,
I have got a tohatsu 2st 25hp that i purchased new late 2005 this is on a 12 ft inflatable.During 2006 i only managed to put 12 hours on the engine,so i only just got pasted the break-in time and still running on 25:1 ratio of oil.
In that 12 hours i managed to run the engine at wot a few times with myself my wife and daughter in the boat and notice that it was only revving up to 4600 rpm(measured on a tiny tach)and 25mph(gps).Is this dew to 25:1 mixture?As i don't want to start changing props yet.The pitch on the prop is 9.6 x 13".

 

[TOHATSU GURU]

Re: tohatsu 2st 25hp

That's slow, but there could be a lot of reasons why:

In order of most likely

1) Boat is not aired up to the correct spec.
2) Engine is mounted too low on transom.
3) Engine trimed wrong.
4) Wrong prop.
5) Boat trimed wrong.
6) Engine has:
Fouled plugs...From double oil.
Improper carb setting.
7) Boat has a crappy design.

 

[tenga]

Re: tohatsu 2st 25hp

Many thanks for your reply.My engine is mounted with the anti cavitation plate 1/2" below the bottom of the boat.I can not get the engine any higher than this as i will not have anything for the clamp screws to hold to on the transom.To check that i am running the right prop does the boat need a light load or heavy load in the boat?

 

[steelespike]

Re: tohatsu 2st 25hp

It doesn't seem to me that 25 is slow with 2 to 3 people in the boat.
I wouldn't think that the 25 is rated for much more than 30 with one person.
What does it run with one person,rpm/speed?
RPM range is 4,800 to 5,500. It would be ideal to prop it for 5,500 with one person then it will perform within range with a load.At 4,600 with 3 people your in the ball park.
If you run like that a lot then you may want to consider a prop change.But be sure to try different trim settings and weight placement.
It would appear the motor could be higher. A jack plate may be an option.
or you could add some height your self.As little as an inch in height could mean 2 to 3 mph.

 

[tenga]

Re: tohatsu 2st 25hp

I have been out by myself in the boat over the weekend with a full tank of 50:1 fuel and oil.I done some long wot runs to check the rpm and speed and came back with figures of 4900 rpm and one run of a top speed of 32mph but the rest of the runs the top speed was 28-30mph at 4900rpm.Is this any good?

 

[TOHATSU GURU]

Re: tohatsu 2st 25hp

It's okay, but not as good as it could be.

Re-visit the list because you are off on one or more of these. In general you should be at 28 to 32 mph with two people in the boat.

1) Boat is not aired up to the correct spec.
2) Engine is mounted too low on transom.
3) Engine trimed wrong.
4) Wrong prop.
5) Boat trimed wrong.
6) Engine has:
Fouled plugs...From double oil.
Improper carb setting.
7) Boat has a crappy design.