2002 Tohatsu 25hp 2 stroke won’t start

[Jamesaelliott]

I’m new here. Last time out it was really running like crap. Hard to start, would slowly bog down and die at idle. It has a fresh bore and new pistons maybe 2-3 hours on it. Anyway, I was running WOT then it slowly idled itself down to half power. Made sure it was spitting water, it was so I killed it. Got back home and checked for spark/cleaned carb. Bottom cylinder had very little spark so I ordered ignition coil. Have great spark now. And now try’s to start But won’t. Then other times while cranking it sounds like it’s not sparking.. I even went as far as tearing the motor down to make sure nothing internal was bad. The bottom cylinder was twice as wet as the other side, I’ve check wiring, grounds, kill switch. Unless I forgot to check something out I’m guessing either the cd unit or coil plate. If that’s the case I’ll just sell the darn thing and get a new to me motor. I’m not playing a guessing game with 300-400 dollar parts. Can anyone help me out? Maybe it’s something simple I’m just missing.

 

[Jamesaelliott]

Also i haven’t done a compression check but the rings and sleeves are in great shape. I didn’t remove the head to check the gasket. I’m lost. It has compression, has spark, atleast when I check it. One plug has every bit of a half inch spark gap, other one sometimes half inch other times a quarter. It’s getting fuel that I know of. It primes, holds prime. Fuel pump Is also new and is working.

 

[pvanv]

Assuming this is an M25C3. You did not mention model. Year is irrelevant.
Did you do the ohm meter checks on the exciter, CD, and siamese coil? The exciter has an MSRP under $80...

 

[Jamesaelliott]

Assuming this is an M25C3. You did not mention model. Year is irrelevant.
Did you do the ohm meter checks on the exciter, CD, and siamese coil? The exciter has an MSRP under $80...

What is the exciter, and no I didn’t. I read that I could test them but I have no clue on what wires to test, how to test or what ohms it should be reading. If the exciter is the little rectifier that charges the battery while running I removed that a long time ago when it burnt up. Motor still ran good. I also removed the electric choke..

 

[Jamesaelliott]

What is the exciter, and no I didn’t. I read that I could test them but I have no clue on what wires to test, how to test or what ohms it should be reading. If the exciter is the little rectifier that charges the battery while running I removed that a long time ago when it burnt up. Motor still ran good. I also removed the electric choke..

Also I don’t know the exact model as I’m not home.. it’s 2 stroke, 2 cylinders, electric start and It’s not a tiller handle. Hopefully that can narrow it down

 

[MattFL]

I'm confused, you said you tore the motor down but also said you didn't remove the head to inspect the gasket. I would personally do a compression check before going too much farther. It could be electrical, but it's cheaper and easier to be 100% sure that the compression is OK. Since it was just apart for new pistons, a leaking head gasket would not be out of the ordinary, especially if there was any error in assembly, such as head bolts not torqued properly, gasket surfaces left dirty or not perfectly flat.

 

[Jamesaelliott]

I'm confused, you said you tore the motor down but also said you didn't remove the head to inspect the gasket. I would personally do a compression check before going too much farther. It could be electrical, but it's cheaper and easier to be 100% sure that the compression is OK. Since it was just apart for new pistons, a leaking head gasket would not be out of the ordinary, especially if there was any error in assembly, such as head bolts not torqued properly, gasket surfaces left dirty or not perfectly flat.

I went through the back half of the crankcase because I didn’t want to remove head gasket and ruin it and risk breaking more head bolts off. When I had the motor apart before to do the rings and pistons I broke 4 bolts off so the machine shop had to fix me up

 

[Sea Rider]

Under no circumstance should you run wot any motor specially if with new pistons, piston rings and cylinder bores. Forgot to do a new 10 hour break in period with 25:1 fuel/oil ratio mix ?

That's a 19 year oldie and I'll bet the cylinder head and exhaust gaskets have never been re torqued to 25 NM with a torque wrench since out of the box. If that's a salt water motor used for that long, expect to break bolts around the cylinder head, exhaust covers and thermo cup as well. A re torque soon after break in period it's mandatory which no one does to avoid that awful scenario. Is the motor well time advance/carb synched per factory specs ? Why did you installed new pistons and rigs for, with oldie ones achieved low cylinder compression, was difficult to start ? Check both cylinder compression again, hope there's nothing already screwed ?

Electric components that old might be having erratic misbehaviours, heats up shorts, misses when the motor is being run under load but shows being within the ohm range and DVA outputs factory stated when cranking, those symptoms are the hardest to troubleshoot and diagnose fast.

Happy Boating​

 

[Jamesaelliott]

I have ran the gas/oil ratio a little more on the oily side since new pistons. I had to get it bored and new pistons due to bad rings which scarred the sleeves.. it ran flawless after rebuild.. on cold engine I wouldn’t even need to manually choke it. It took a few seconds to fire but once she was warm she’d fire right up. Now it wants to start, it tries so hard but just won’t. It will hit that stage where the starter disengages. Then it just cranks like it has no spark, or fuel. I turn key off and it will try to start again. Same cycle over again.

 

[MattFL]

Start with the easy stuff. Check the compression. Then fuel. Then spark. Are the reeds in that motor metal or plastic/fiber?

 

[Jamesaelliott]

It’s getting fuel that I know of. Pump is pumping fuel while cranking. It’s getting spark when I test them. Pulling the rope, to me feels like it has plenty of compression. It tries to fire but once the starter disengages I let off key and hit it again it acts like it’s not getting fuel or spark. Just a spinning motor

Start with the easy stuff. Check the compression. Then fuel. Then spark. Are the reeds in that motor metal or plastic/fiber?

 

[MattFL]

Something is not working so it's time to get scientific. "Feeling" like it has compression is a lot different than measuring and knowing for sure. The compression may very well be fine, but if you check it then you'll know 100% for sure so you can mark it off the list and move to the next thing. One less variable.

 

[Sea Rider]

Adding little more oil isn't the same as running 25:1 right after the new pistons were installed which the factory recommends going for. Did you installed oversized pistons and ringd after boring both cylinders ? The cylinder head was mandatory to tear, decarbon, clean the internal water passages and install a new head gasket torqued to specs. A machine shop would have taken care of any broken bolt at an extra cost. I am of the idea if you are going to repair it, repair it well....

Happy Boating​

 

[Jamesaelliott]

So the problem was a blown head gasket. I’m not sure why it would blow with it being new. Maybe not having it torqued correctly, maybe I need to get the block resurfaced, maybe because I didn’t correctly break the motor in after new rings, pistons and gasket? I ordered a gasket, will install and torque to spec this time and go a little easier on it for a while.

 

[MattFL]

Most likely it wasn't torqued to spec or the tightening order wasn't followed, or a surface was not flat or clean. Or an overheat can also do it. Before you re-assemble it, get a strait edge and check both the head and block to be sure they are flat. If they're not then that has to be fixed or you'll be right back at square one very shortly. To clean the surface do not use any spinning tools. No dremmels, no wire wheels. Those can leave the surface non-flat. If it needs more than scraping to clean up, you can put a piece of sand paper on glass or something else flat, lay the head or block on the flat sandpaper and drag it around. Or have a machine shop resurface it.

 

[Jamesaelliott]

Most likely it wasn't torqued to spec or the tightening order wasn't followed, or a surface was not flat or clean. Or an overheat can also do it. Before you re-assemble it, get a strait edge and check both the head and block to be sure they are flat. If they're not then that has to be fixed or you'll be right back at square one very shortly. To clean the surface do not use any spinning tools. No dremmels, no wire wheels. Those can leave the surface non-flat. If it needs more than scraping to clean up, you can put a piece of sand paper on glass or something else flat, lay the head or block on the flat sandpaper and drag it around. Or have a machine shop resurface it.

Would you happen to know the torque spec and correct order to go in?

 

[Sea Rider]

Now you've learned the hard way that when breaking in the new pistons and rings need to run the motor with 25:1 fuel/oil ratio for the next 10 hours, that means adding double 2 stroke oil dose to the normal 50:1 oil/fuel ratio. Check the Tohatsu's break in period chart in the Owner's Manual and follow them to the letter. The head torque is 30 NM and the torque sequence is done as follows :

With powerhead facing upwards :
9---------10
5---------6
1---------2 **
4---------3
8---------7

Start at middle bolts (**) at 1 and torque all bolts clockwise following this pattern. Try doing it as stated with 3 individual one step at a time torqued bolts to 10-20-30 NM steps (Newton/Meter)

If that motor has high hour use in salt water would recommend to remove the side exhaust covers to decarbon the complete exhaust chamber and associated water passages as well. Will probably need to order 2 new cover gaslets as may be dried and break once being removed. Perform same on the combustion chamber, associated water passages. Motor will run and cool as a champ....

PD, can pass that 25 to a 30 HP for peanuts cost, just order the 30HP carb unrestricted gasket part number : 346-020110 if not been superseded. Will need to perform a new carb/timing advance to match the 30 HP tech specs which differ from the 25 HP motor, can be done under 15 minutes..

Happy Boating​

 

[Jamesaelliott]

Now you've learned the hard way that when breaking in the new pistons and rings need to run the motor with 25:1 fuel/oil ratio for the next 10 hours, that means adding double 2 stroke oil dose to the normal 50:1 oil/fuel ratio. Check the Tohatsu's break in period chart in the Owner's Manual and follow them to the letter. The head torque is 30 NM and the torque sequence is done as follows :

With powerhead facing upwards :
9---------10
5---------6
1---------2 **
4---------3
8---------7

Start at middle bolts (**) at 1 and torque all bolts clockwise following this pattern. Try doing it as stated with 3 individual one step at a time torqued bolts to 10-20-30 NM steps (Newton/Meter)

If that motor has high hour use in salt water would recommend to remove the side exhaust covers to decarbon the complete exhaust chamber and associated water passages as well. Will probably need to order 2 new cover gaslets as may be dried and break once being removed. Perform same on the combustion chamber, associated water passages. Motor will run and cool as a champ....

PD, can pass that 25 to a 30 HP for peanuts cost, just order the 30HP carb unrestricted gasket part number : 346-020110 if not been superseded. Will need to perform a new carb/timing advance to match the 30 HP tech specs which differ from the 25 HP motor, can be done under 15 minutes..

Happy Boating ​

if I run a 30hp carb, how do I advance timing?​

 

[MattFL]

I THINK this manual covers your motor, look up the actual model number and double check me:

Tightening head bolts:

TOHATSU NB-1000 Service Manual (Page 116 of 269) | ManualsLib

www.manualslib.com

I didn't see the torque value listed in that chapter, so I believe you would follow the torque from the general table on this page (double check that hte head bolt torque isn't listed explicitly):

Service Specifications; Standard Torque Values - TOHATSU NB-1000 Service Manual [Page 14]

TOHATSU NB-1000 Manual Online: service specifications, Standard Torque Values. Standard Torque Values Size M4 M5 M6 M8 M10 These Torque Values Apply Only When A Special Torque Specification Is Not Listed In The Special Torque Values Chart At The Beginning Of Each Section. 1-/ 2-Cylinder...

www.manualslib.com

Tohatsu recommended break-in of new parts:

Break-Ln Procedure; First 10 Minutes (0 - 0.16 Hours); Next 50 Minutes (0.16 To 1 Hour); Next Hour (1 To 2 Hours) - TOHATSU NB-1000 Service Manual [Page 36]

TOHATSU NB-1000 Manual Online: break-ln procedure, First 10 Minutes (0 - 0.16 Hours), Next 50 Minutes (0.16 To 1 Hour), Next Hour (1 To 2 Hours). Failure To Follow The Break-In Procedure In Owner's Manual And Special Fuel Mixture Requirements For Break-In May Lead To Serious Engine...

www.manualslib.com

 

[Sea Rider]

Hey Mat, can you tell what's the double post for ? I currently sell and service
those and own one so to speak with proven knowledge...
​