Tohatsu 50 mystery

[gyroplanes]

My Tohatsu 50 has been running like a charm. I haven't run it over 7mph for a few years, using just enough throttle to reach that speed.
Yesterday, I ran her at full throttle and after about 10 minutes, it shuts off completely.

My son's friend was aboard and he said that happens all the time at full throttle, and, not to worry, it will start right up again.......it did. He said he and my son had this happen often last year.

I did some testing and here are some facts;
It has new fuel and plenty of oil in the bottle
The vent was open and the squeeze bulb not collapsed . It also was full of fuel
I replaced the plugs this winter
I cleaned the oil and fuel strainers and their "cups"
I ran the motor at various RPMs and did not encounter the shutdown until after 4,000 RPM

ANY IDEAS?
Thanks, Tom

[Catigale]

Magneto wiring? Cutoff switch loose? Sounds electrical in nature.... Tough one....

[Divecoz]

Could it be a REV Limiter? My Road Bike has one ( its just a module) It Eliminates the ability to Power Shift at WOT.. Some remove them I left mine on..

[raycarlson]

what year and model, TLDI ??

[Tomfoolery]

Any chance it's overheating and shutting down automatically? Is the engine actually reaching the specified WOT speed range with WOT? I think it's 5000-5700 rpm, but don't quote me on that.

Overspeed is another possibility, as stated, but I haven't a clue how it works on a Tohatsu.

[Catigale]

I think most rev limiters don't cut the motor when you hit the WOT, the motor will just stay at rated revs. Anyone with a Tohatsu care to add to that?

[ualpow]

Not too familiar with 2 cycle outboards but maybe a vacuum leak? What about spraying starting fluid near vacuum lines and see if RPM increases? Ether way (pun intended) it sounds like its not getting fuel at high RPM.

[Hardcrab]

No relation at all with a 2004 90hp TLDI Tohatsu, but when I was underpropped, my rev limiter kicked in at 6,500 or so and cut ignition(?) until about 6,200 or so.
Then the engine went right back to 6,500 and the whole process repeated itself until I backed the throttle down.
5,800 is advertised "max" suggested rpm for this engine.
Prop was a 14" x 10" pitch.

The engine did not die as the 50 is doing.

[Divecoz]

Rev Limiters force you to decelerate "so to speak " they tend to Bog down lose power almost like its running on 1 cylinder or you have pulled the compression release .. Humm But I have never heard of one shutting OFF the engine..

[kelseydo]

Had the same problem with my Nisson 50. Turned out the pickup in the tank was sucking air. Finally ended up replacing the pickup assembly. It could also be the fuel pump.
Dan

[gyroplanes]

Thanks for all the replies.

I can cruise all day at 4k or less, give it WOT and after 5-10 minutes, it flat shuts off. Close the throttle and crank it right back up, under 4 k rpm, all is good, WOT and it shuts off again. I only went through this cycle several times, but I have a hunch it will repeat all day long.

I don't know the year or model (info is all in the boat) but it is around 1996-7 vintage, 3 cylinder, carbs. New plugs, new fuel and runs great except.........
Tom

[Tomfoolery]

Sure sounds like the tank vent is not fully open, but that's already been suggested.

[MacTommy]

Any water separating filters you can drain? Clogged filter somewhere, maybe at the fuel tank pickup?

Long time storage of two-strokes may also cause two-stroke oil stored for some time in the carburetor drying up and leaving clogged nozzles or stuff. But this is an injection engine?

[jbgibbs99]

If you (or PO) are in salt water read on. I had a similar problem with mine last year. It turned out the PO hadn't flushed it well (or used it much) and the thermostat was salted up preventing it opening properly and causing overheating (although the buzzer didn't go off) and cutting the revs.

I took the thermostat out (round bulge with three bolts at the front of the engine) cleaned off the salt and then chiseled (yes chiseled!) all the rock-solid salt out of the housing. I also tested the thermostat by dangling it in a pan of water and bringing it to the boil making sure that it opened up as the water reached boiling.

It seemed to solve the problem, but I have yet to give it an extended blast.

Given the extent of the salt I guess I am going to have to take off the exhaust cover and clean out the water chamber at some point.

Cheers,
Bruce

[gyroplanes]

Rule out water or blockage up to the engine. New fuel, new oil, squeeze bulb not sucked down, fuel delivery is good.
Filters cleaned

I doubt it a "seizure" only because it shuts down fast, like a shut off key (or safety lanyard pulled) and will restart and run just fine in a few seconds after cranking. I believe a seizure would cause a slow starter cranking due to cylinder friction drag, but that doesn't happen.

The real mystery is that it will run all day at 4k RPM and that it doesn't lose a cylinder, it shut down all three.

I am leaning toward an electrical issue, but in denial as that would be very hard to prove out unless I had parts to swap out.

Calling the dealer is next.