Tohatsu 20hp Under performing

[Boisegolfer]

I am having issues with a 2012 Tohatsu 20hp long shaft. Slow speed, water coming up the transom, not planing.
I raised the transom 2 1/4" and the water issues have settled down but I still have no speed. I bought one of the small inductive TACHs and my WOT is 2650. GPS speed is 11 to 12mph.
I have a Harbercraft 1400sk, boat, motor, gear and 2 people weigh about 1000lbs (this is a guess).

 

[pvanv]

Re: Tohatsu 20hp Under performing

Hard to say from the photo, but your height may be OK. Is the antivent plate even with the bottom of the boat? What pitch are you running?

 

[Sea Rider]

Re: Tohatsu 20hp Under performing

Some issues :

1-Probably yout boat needs a short shaft engine and you are using a long shaft ?
2-Is engine going into full wot (wide open throttle) or has a restriction of some kind ? 2650 is really way low
3-Have you trimed your engine to be perpendicular to water level once boat is floating ?
3-Where is water flow passing, still over small upper plate at wot ? If so, excesive water drag on tail, will slow you down hard.
4-Check if at wot you can achieve this example ; http://www.youtube.com/watch?v=oBeZjaA76VM&feature=youtu.be
5-Is your prop brand new and came factory delivered ?
6-This is a classic example of inproper transom height, water up transom, bad music and planing frustration.

Transom height needs to be corrected under trial and error and on water....

Happy Boating

 

[Boisegolfer]

Re: Tohatsu 20hp Under performing

Yes, it is even with the bottom of the boat. Don't know the pitch but I will look. It is the prop that came with the motor......motor has approximately 12 hours on it.

 

[Boisegolfer]

Re: Tohatsu 20hp Under performing

The Prop is a "9" pitch.

 

[Boisegolfer]

Re: Tohatsu 20hp Under performing

1- it is a boat the requires a long shaft motor
2- As far as I can see the throttle is opening as expected, all the way to the stop. I have not removed the carb.
3- I have tried all 6 trim hole with very little difference from one to the other.
4- Very similar
5- Yes, 9 pitch
6- I had a transom adapter made at a local machine shop that raised the motor 2 14". Your picture was what I had before I raised the motor.

 

[TOHATSU GURU]

Re: Tohatsu 20hp Under performing

The water coming up the transom is a dead giveaway of an incorrect installation, almost certainly due to the engine being to low on the transom. What is the actual transom length at the center? With a long shaft model engine the transom would need to be at least 21 1/2 inches high to start. Once you get the engine exactly where it needs to go on the transom you can start playing with the prop. You will probably wind up with a 7 pitch, but the transom height needs to be done first. I'm not convinced there isn't something wrong with the engine too. Could be a jet issue. What elevation are you using it at?

 

[Sea Rider]

Re: Tohatsu 20hp Under performing

If engine does not sit at correct engine/transom heigh you could play all day long with trim with no aval...trim to have boat and brand sticker paralell to sea level once floating, then adjust tune height accordingly. Must be done under trial and error. Check prop pitch too.

Happy Boating

 

[Boisegolfer]

Re: Tohatsu 20hp Under performing

The elevation is 3176. The transom height before the elevator was 20" now it is 22 1/4".

 

[TOHATSU GURU]

Re: Tohatsu 20hp Under performing

I would get it into a dealer. You should be fine on the height now. Even with a 2" pitch change you aren't going to be where you need to be and your elevation is just to the point where you could do a jet change and reap a reward in performance. If the dealer says's there isn't anything wrong with the engine I would really look hard at the altitude as being a issue for you.

 

[Boisegolfer]

Re: Tohatsu 20hp Under performing



These pictures may help.

 

[TOHATSU GURU]

Re: Tohatsu 20hp Under performing

The engine still looks low on the transom too. Also, you should be doing 18 or so on that boat with a 450 kg load.

 

[Boisegolfer]

Re: Tohatsu 20hp Under performing

I found a local authorized service location....I will call and make an appointment. The engine never sounds like it is revving up, idles great trolls all day.

 

[catfighter]

Re: Tohatsu 20hp Under performing

I found a local authorized service location....I will call and make an appointment. The engine never sounds like it is revving up, idles great trolls all day.

Fwiw my boat (in the example above) is going 22knots at 3/4 throttle. I raised it up another 1/4" to get rid of the spray.


Also I agree wot should be closer to 5000rpms

 

[Sea Rider]

Re: Tohatsu 20hp Under performing

If it's a 4 stroker, wot should be close to 6100 rpm.....

Happy Boating

 

[fishndirk]

Re: Tohatsu 20hp Under performing

True. I run mine on a 14 ft Alumacraft. Average load between 700 and 750 pounds and 26mph right at 6100rpms. Mine is a short shaft though, transom measures 14 7/8 inch high which puts the AV plate about 1/8 inch bellow the bottom edge of transom. Could probly raise it up a quarter inch or so and reduce the drag a bit. If your achieving under 3000rpms and your motor height is right, then you definately got another problem.