05' Tohatsu 15 4 stroke. Starts and dies within seconds.

[Wee Hooker]

Ok, admittedly I'm a 2 stroke guy ( and am pretty handy in fixing them) but when my 95' merc 15 hit the wall, I decided to take a chance on a newer 4 stroke. Found this one that was very clean, had low hours (used marginally as sailboat tender) and was maintained yearly at the local Tohatsu dealer. It also got a brand new carb at that dealer in 2019 as well. When I bought this engine just a month back, It started right up (cold) after 3-4 pulls in the sellers yard and ran fine . Restarted first pull several times after it warmed up too. Now I get it home and after it sat unused for a few weeks it's been a SOB . Took a dozen pulls to get it to cough. Now I can get it to start regularly but it will only run/idle for 10-20 seconds ( just long enough for the oil light to go out) then stalls regardless of what I do. Squeezeing the ball while it runs has no effect. Moving the throttle position up while it runs ( even to the restart mark) seems to make it die immediately. Tapping the carb (to free a possibly sticky float) has no effect either. Tank, primer and line are brand new ( as is the gas). I've also verified that the fresh gas is getting to the carb . I've also verified good spark at plugs. As an aside, once it stalls, it often needs to sit a few min before it will start again. I suspect it is either that mysterious auto choke system / the carb is running too rich. Any thoughts/experience on these older carbonated engines is greatly appreciated as I'm running out of ideas!

 

[pvanv]

You did not mention exact model. Probably MFS15B2. That does have ABS cold start enrichment. Very reliable, and easy to test. If too rich, the plugs would be wet. Are they?

 

[Wee Hooker]

You did not mention exact model. Probably MFS15B2. That does have ABS cold start enrichment. Very reliable, and easy to test. If too rich, the plugs would be wet. Are they?

Thank you for taking the time to respond. You're expert input is greatly appreciated.
Yes, you have the model number correct. I didn't know what they call it but it does have a automatic choke of some type . I assume it is that white elbow looking thing sitting on top of the carb. So I just went and tested. After the motor started and stalled , I pulled both plugs to inspect. Both were wet ( not soaked) with an oily fuel residue,. Enough so it easily wiped off easily onto my fingers. Plugs are like new from earlier this season. So is there a way to test the auto enrichment operation? Should I just replace it? Can it be adjusted ( Seems to turn with little resistance and I'm not sure if it's position sensitive.)

 

[pvanv]

The ABS solenoid is an expanding wax capsule with a heater in it. If you apply 12v to it, you should see the needle slowly lengthen. As long as it's seated, all should be good. The carb must be impeccably clean. Also verify oil level below the full mark.

 

[Wee Hooker]

The ABS solenoid is an expanding wax capsule with a heater in it. If you apply 12v to it, you should see the needle slowly lengthen. As long as it's seated, all should be good. The carb must be impeccably clean. Also verify oil level below the full mark.

Will verify all in the next couple of days and report back. Thanks again.

 

[Wee Hooker]

The ABS solenoid is an expanding wax capsule with a heater in it. If you apply 12v to it, you should see the needle slowly lengthen. As long as it's seated, all should be good. The carb must be impeccably clean. Also verify oil level below the full mark.

You Sir, are my hero! I was just getting ready to trouble shoot the carb further and noted your last statement about oil level. So I relooked at the dip stick and noticed that the oil level was a good 3/4" above the top/full mark. (I did have the motor running once before but the power head was much more level when it was on the stand. Now that it is on the boat and trimmed, it angles back a bit.) I figured I'd take a chance and siphon some oil off (rather than drain it all) to see if that had any effect. To my surprise, I had to take a full 8 oz out of the engine to get it to the top mark on the dipstick. Once that was done, the engine started from cold and ran like new with one easy 1/2 pull. Being a 2 stroke (old) guy, I never would have thought of excessive oil level as being the culprit. (When the oil pressure light blinked out on start, I thought it meant oil was good to go.)
That said, I'm a little concerned that the motor had a full 8 oz extra oil in there. It doesn't appear to have water and doesn't smell of gas (nor will it flash off with a flame) so I'm thinking it was just inattention by the last person to service the engine. The oil looks somewhat dirty so it's time to change it all anyway. I'll get that done (to the manuals recommendation) and keep a close eye on it from now on. Can't tell you what a thrill it is to have the motor running great again. Not only did you save me allot of money but likely salvaged my fall fishing season as well.

 

[Wee Hooker]

You Sir, are my hero! I was just getting ready to trouble shoot the carb further and noted your last statement about oil level. So I relooked at the dip stick and noticed that the oil level was a good 3/4" above the top/full mark. (I did have the motor running once before but the power head was much more level when it was on the stand. Now that it is on the boat and trimmed, it angles back a bit.) I figured I'd take a chance and siphon some oil off (rather than drain it all) to see if that had any effect. To my surprise, I had to take a full 8 oz out of the engine to get it to the top mark on the dipstick. Once that was done, the engine started from cold and ran like new with one easy 1/2 pull. Being a 2 stroke (old) guy, I never would have thought of excessive oil level as being the culprit. (When the oil pressure light blinked out on start, I thought it meant oil was good to go.)
That said, I'm a little concerned that the motor had a full 8 oz extra oil in there. It doesn't appear to have water and doesn't smell of gas (nor will it flash off with a flame) so I'm thinking it was just inattention by the last person to service the engine. The oil looks somewhat dirty so it's time to change it all anyway. I'll get that done (to the manuals recommendation) and keep a close eye on it from now on. Can't tell you what a thrill it is to have the motor running great again. Not only did you save me allot of money but likely salvaged my fall fishing season as well.

Update: I had the materials so I just did a quick oil change. When I did, I measured the rest of the oil that drained from the motor at just about 33 oz. ( Which is what the manual states as capacity BTW) That means it had around 41 oz before I started!

 

[pvanv]

Good idea to change the filter as well.

 

[Wee Hooker]

Good idea to change the filter as well.

I did.

 

[MattFL]

This is the first I've ever heard an engine turn off from oil too full, I've only seen oil pressure switches that kill the motor when the pressure drops too low (indicating low oil level). Is there actually a too-full sensor, or was the high level just allowing the oil to get whipped up into a foam causing the pressure to drop? I learn something new every day!

 

[pvanv]

This is the first I've ever heard an engine turn off from oil too full, I've only seen oil pressure switches that kill the motor when the pressure drops too low (indicating low oil level). Is there actually a too-full sensor, or was the high level just allowing the oil to get whipped up into a foam causing the pressure to drop? I learn something new every day!

It died of extreme crankcase pressures and foamed up oil.

 

[Panhandle Nick]

The ABS solenoid is an expanding wax capsule with a heater in it. If you apply 12v to it, you should see the needle slowly lengthen. As long as it's seated, all should be good. The carb must be impeccably clean. Also verify oil level below the full mark.

Hi pvanv, maybe my problem is similar. I have an NSF 15C 2009 4 stroke. IS it possible that oil too full could be my problem? Or when I lifted it with my cherry picker if I tilted it the wrong way, would that prevent starting? Thanks, Nick

 

[pvanv]

You really should start a new thread. But yes, over full oil can be an issue. And if you end up with the tiller up, yes, you can get a liquid locked cylinder.

 

[Panhandle Nick]

You really should start a new thread. But yes, over full oil can be an issue. And if you end up with the tiller up, yes, you can get a liquid locked cylinder.

I did check my oil level and it was ok. I did remove the new plugs to see what they looked like and the look brand new. Even after Mike cranks. This motor is electric start and the starter and flywheel are functioning fine. Are you saying oil can get past the rings and into the combustion chamber?

 

[pvanv]

Yes, if the motor is laid down on the wrong side.

 

[Panhandle Nick]

Ok that's a possibility. After multiple cranks wouldn't the plugs have oil residue on them? They don't.
How common would it be for the belt to skip a tooth or something and throw the timing off. Although the belt looks brand new and the teeth on the sprocket are all fine.

 

[pvanv]

Oil in the cylinder would cause a liquid lock, aqnd you would not be able to crank. I would verify good spark and clean the carb properly.

 

[MattFL]

Just to file this away for future use; having had a few engines with a cylinder full of oil over the years, if you keep steady firm pressure on the pull rope (or kick starter) the oil will eventually escape the cylinder, some of it around the piston and some of it out the exhaust if it has a compression release, at which point you'll be able to start it. This has happened a few times on our dirt bikes and motorcycles that pipe the crank case vent into the airbox. If you fall in an awkward position, the vent dumps enough oil into the intake that the cylinder fills with oil when you try to start it. No harm done, just be patient with the pressure until it spins over freely, then all you have is a bit of mess and a lot of smoke until the oil burns off.