25/30 hp Tohatsu problems

[Shadow1A]

I have a 2001 30 HP Tohatsu, serial # 62786 model # M25C3-372. I normally run around 28 - 29 mph. Ran it yesterday and couldn't get over 18 mph. After I stopped the engine, I had no problem restarting it but as soon as I would put it in gear (reverse or forward) it would die. Any help would be greatly appreciated.

 

[Sea Rider]

Welcome to IBoats,

Was 18 MPH achieved at full throttle grip after been running 28-29 MPH ?

Things to know :

The motor is used in fresh or salt water, is the fuel tank immaculate clean along the motor's fuel filter, are spak plugs old or fresh, run the recommended ones well gapped, how about the carb, has been cleaned lately, run carb dry after each outing, has low, medium high or high hour use ?

Happy Boating

 

[Shadow1A]

Top speed last trip was 28 (Friday) and top speed this trip was 18 (Wednesday). Boat is only used in fresh water. Spark plugs are less than a month old, do run the recommend plugs. Carb was cleaned 2 weeks ago. I don't run carb drive after each outing because I fish multiple times in a week normally but never more than a week apart between runnings. Motor is a 2001 so I would say high hours on it. Thanks

 

[Sea Rider]

Being a 19 year oldie, probably with a spun prop already or on its way to become one if loosing +10 knots between both runs. Make a hub test run at wot to determine if so. If the motor dies at low rpm when put forward or reverse seems the fuel/air mixture screw or the idle rpm screw are out of adustment ? Increase a bit the idle screw + 5 degress clockwise to increment the idle speed a bit and check.

Does the Tohatsu 25 HP comes factory delivered with a 13 pitch prop. Which type and boat size is being powered with said motor ? You could turn that nice 25 HP to a 30 HP one for peanuts costs while maintaining decent fuel comsumption.

Happy Boating

 

[Shadow1A]

I am running it on a 15/44 Aluminum John boat (Express). I have had the motor turned into a 30 years ago at a local mechanic shop. I have had to have a lot of cup added to the prop because I was having problems with speed about a year ago. Solved the speed problem but absolutely killed my hole shot (time it takes to get on plane). My nephew is supposed to be tearing it down for me this weekend to see the extent of the problems. I will let you know. Thanks for the help and if you have any other suggestions, I would be glad to hear them. Thanks again!

 

[Sea Rider]

Tearing it down will be useless, let's go little by little...

Assume that for the 30 HP convertion the shop swapped the 25 HP carb gasket for the 30 HP one which has a much wider middle air hole. The 30 works with 25 time advance while the 25 with 20, is the current time advance set to 25 deg one along carb gasket ?

Beside these 2 issues, there are other ways to improve the hole shot that can tech discuss later once knowing what inquired.

Happy Boating

 

[Shadow1A]

Well my nephew found the problem, blown head gasket. Got it changed out and now it runs like it is supposed to. Thanks for all the help.