Tohatsu 25hp runs good wot, wont run slow for long ?

[phillnjack2]

Ok this is a wierd one for me.
But im sure there is planty of good advice from those who know about these engines.

25HP tohatsu 2 stroke. from first starting it will idle ok in nuetral then put in gear,give it
wide open throttle and it takes off real good.
Infact power is instant.
It will run full throttle like a dream, then when you slow down it will run ok for about 2 mins then will start to realy bog down and vibrate bad.
If you dont give it a twist of the throttle to bring revs up high it will stop completely,
then have to start all over again.

If you leave the engine once stopped for 2 or three minutes it will be fine again, untill you slow down.
If we keep the throttle wide open it will stay running realy good and strong for ages.
The engine is on a 4 metre inflatable, with 1 person around 25mph, with 3 people 23mph ,so the full throttle is pretty good, and like i say will keep running no problem at WOT.
I have cleaned every single part of fuel system over and over again,checked for air leaks,changed fuel line etc.

The engine is an old 1980's M25-A2 model, 2 Cylinder 2 stroke ,short shaft,with electric start etc.

COULD THIS BE A COIL PROBLEM, its a double type coil ??????????

Any advice on this would be realy welcome.

phill

 

[pvanv]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

Could be an ignition issue... Could also be insufficient oil in the pre-mix, so verify that you are running 50:1 TCW-3. Check plugs. If they are too white, you are running too lean, resulting in running too hot, resulting in too much friction at hot idle. If all that checks out, then... When the problem is happening, stop and run through the electrical tests in the Factory service manual to see if you can find a resistance that is off.

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

The engines runs very cool, we have no problem keeping our hands on
the engine either WOT or at idle.
Tons of water also comming out of exhaust and tell tale.
Oil is 50 to 1 ,infact might be a touch more oil ?
Will check if the oil is TCW-3, if not will try with quicksilver marine 2 stroke oil.
If we had a factory manual we might be able to check a few things,
but have you tried tohatsu for anything like info or manuals ?
Tohatsu is terrible for anything other than a new engine, once engine is sold from
their agents, it seems they dont want to know.
we cant even get info on what wire colours to use for the kill switch !!!!!!
Tohatsu say "they dont know what colours due to age of engine"
so dont they expect any of their products to last long ?
if it was evinrude/ johnson ,mercury etc we would get info, as their engines are often 40 years old.
Forums like this are our only hope.

we have another coil and gonna give that a try , but is there anything else we can
check without having expensive electrical testing equipment.
In the uk testing equipment is very very expensive.

This engine is so good at full throttle, and a good holeshot for a 25hp.



phill

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

The engines runs very cool, we have no problem keeping our hands on
the engine either WOT or at idle.
Tons of water also comming out of exhaust and tell tale.
Oil is 50 to 1 ,infact might be a touch more oil ?
Will check if the oil is TCW-3, if not will try with quicksilver marine 2 stroke oil.
If we had a factory manual we might be able to check a few things,
but have you tried tohatsu for anything like info or manuals ?
Tohatsu is terrible for anything other than a new engine, once engine is sold from
their agents, it seems they dont want to know.
we cant even get info on what wire colours to use for the kill switch !!!!!!
Tohatsu say "they dont know what colours due to age of engine"
so dont they expect any of their products to last long ?
if it was evinrude/ johnson ,mercury etc we would get info, as their engines are often 40 years old.
Forums like this are our only hope.

we have another coil and gonna give that a try , but is there anything else we can
check without having expensive electrical testing equipment.
In the uk testing equipment is very very expensive.

This engine is so good at full throttle, and a good hole shot for a 25hp.



phill

 

[TOHATSU GURU]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

Historically, the Japanese have always looked at machinery as having a built in expiration date. It goes across all brands and types of products. The kill switch wiring code has never changed...Black and brown. How could you have an engine for thirty years and not already have a service manual?

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

I have not had this engine for 30 years, its a friend who owns it and he
has only had it about 6 months from what i gather.
as for black and brown ?

we have Black, white, green, yellow and Red, no brown in the loom lead.

but there is a brown wire at the coils, would this be the brown you speak of ?.


phill

 

[pvanv]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

"Tohatsu is terrible for anything other than a new engine, once engine is sold from
their agents, it seems they dont want to know."

Wrong. Your Factory service manual is Part# 003-21035-1, $44.17, available from any dealer, including me.

"we cant even get info on what wire colours to use for the kill switch !!!!!!
Tohatsu say "they dont know what colours due to age of engine"

Wrong again. The stop switch colors have always been brown and black.

What is your precise model/serial? Where are you located? You can find a dealer at http://www.tohatsu.com/dealersearch/index.html

 

[TOHATSU GURU]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

I have not had this engine for 30 years, its a friend who owns it and he
has only had it about 6 months from what i gather.
as for black and brown ?

we have Black, white, green, yellow and Red, no brown in the loom lead.

but there is a brown wire at the coils, would this be the brown you speak of ?.


phill

It sounds like this is a dead engine that you are trying to put into running condition...Without any knowledge of how to do so. I would urge you to tell your friend that he needs to take the engine into a dealer(bad idea since parts are not available for one that old) or tell your friend to put it back into the trash pile where he found it.

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

Model M25a2 serial number 21881

In the uk its not so easy to source a manual for this engine

I live in berkshire, England.

Most outboard mechanics here, dont even want to know anything about tohatsu engines.
Even contacted the Tohatsu factory, they said they didnt know wire colour codes for
that model of engine.
And said they dont have a manual that covers it.

Now how is the engine DEAD ?
it runs very well at full throttle, 24mph on 4 metre avon with 2 people on board is not a dead engine.
the weight of both people was around 440 pounds total. 25 kilo of fuel.
will also run very well at idle in nuetral.
Its just the slow running in gear that is the problem.

 

[TOHATSU GURU]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

I'll rephrase it. You have a 30 year old engine with no parts availability, no service manual and no mechanic. So, it's a geratric patient just waiting to to move into the light. My best advice is to move on to a different project. But, if you really want to screw around with this thing, start with the carb. If you are really lucky it might just be a port or jet in the carb that is varnished shut.

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

Do you know if the fuel pump fitted to these engines is the same or similar to
anything that we could buy nowdays incase that has a spilit in the diaphram or needs seals ?
Dont want to disturb it realy, but thats my next port of call, ive already given
the carb a real good going over, there was dirt in there,But its very clean now.
I dont how the thing was even running at all by the state of the carb for gum etc.

 

[TOHATSU GURU]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

Send me your email address and I will send you the service manual for your engine in PDF. Do not distribute it.

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

That would be fantastic

Dowmes978@btinternet.com
or phillnjack@hotmail.com

would be good to have a look at a real manual for this.
who knows i might get this running perfect.

phill

 

[Sea Rider]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

If it would be gas pump diaphragm issue, will have bogging trouble at any throttle range, anyway check pump interior, small valves, etc. This is a actual Tohatsu 25/30 HP 2 stroke model, probably gas pump is same as this one. If you say engine runs very well, but slow under gear, check tail oil for gear swarfs/limays, or probably you are under propped missing medium to max revs.

Happy Boating

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

yes the fuel pump looks the same as that one.
The engine runs very good at Full throttle, it even picks up very fast in gear.
Its just when trying to go slow it runs very rough then stops.
When started again it will run , then open throttle and it will pick up real good.
But when again trying to go slow after 2 or 3 mins will stop.
Prop is about right size for engine, as it picks up to full speed real good.

thanks fuel pump pic

 

[Sea Rider]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

Has somebody played with engine linkages, rods, stoppers, prob engine out of correct adjustment ?

Happy Boating

 

[phillnjack2]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

No this engine is not like the later ones.
the throttle has nothing to do with timing movements.
No rods that alter timing etc.

anything over half throttle and the engine is perfect.
A real little powerfull engine, just the slow running is so bad.
Im thinking fuel pump seals or coil now.

could also be the rpms are too low.
the manual says 1000 rpms in gear and 1100 in nuetral !!!!

we shall be doing lots of checks over the next week.


phill

 

[Sea Rider]

Re: Tohatsu 25hp runs good wot, wont run slow for long ?

Those rpm are normal factory settings at idle/ralenti speed, check fuel pump external gasket for tightness/wear against engine body, interior leaf/check valves for deformation, probably non flat & not closing properly, carb float valve tip for wear issues, float conditions for deformation, bad fuel level height ? Good luck on your findings...

Happy Boating

 

[bjornbulhoff]

Hi there,

I just read with big interest your thread from 2011. I got the same engine last year and it actually has totally the same problem as you described. Starts easy, good acceleration, making 22 knots on my 17 feet while going to my fishing spots, arriving there, putting it in free, preparing my rod and want to start trolling, starts going unround and stops, if not giving high amount of throttle. So I actually wonder, did you manage to figure out where the problem was? Would be nice to hear from you.

 

[phillnjack2]

it turned out to be bad coil. as soon as it got warm the coil started acting bad.
these older tohatsu had a double coil, and they are like finding rocking horse poop.
we just put 2 x Johnson coils on it and its now perfect, easy to start idles well and throttles up better than ever.
top speed so far 26.1mph
.