Tohatsu 8hp Problems. What's your diagnosis?

[Chotu]

Like many 4 year olds, my tohatsu 8hp has been acting up.

I had some old gas that sat in it for 2 years. Marine fuel, non-ethanol, used marine Sta-bil to preserve it. The same fuel is running fine in a Honda generator as well as in Evinrude etec outboards.

However, I kept getting intermittent stalling and being unable to start the tohatsu after the stalling. It would run great for 10-15 minutes, then after hitting some chop seemed to want to stall and would run roughly, especially at low RPMs.

It did stall and strand us 4-5 times where we needed a tow.

I got new gas (all they sell at the fuel dock is ethanol garbage??). Drained the carb, had all the old gas disposed of from the tank and fuel line.

The outboard ran great for several long runs but started wanting to stall again after some high speed runs.

Here's where it gets weird!
.
It stalled out right at the boat this last time. I didn't bother looking at it and took the launch a couple times. Now, it's nearly impossible to pull start it!

I can (with tremendous force) get the engine to rotate/crank very, very slowly. Then, as it starts moving, it gets easier and easier to rotate/crank the engine. But it won't start anymore.

It's as if the engine is seized, but as I crank it, the oil lubricates it and makes it easier to crank.

To me, this can only be a seized engine or a very strange valve problem.

Any ideas on what is wrong with this very new engine???

I bought it brand new to just invest into a good outboard for once and it's really bad. I expected more than a a few dozen hours out of this thing before it had a fatal issue.

So does anyone have any ideas About what might have happened? Oil is full.

[GILow]

Just a clarification because I can't see your location in your profile. Are we talking two stroke or four stroke here? A four year old outboard in the US would most likely be four stroke, but here in Oz it is more likely to be a two stroke. Elsewhere... I have no idea.

Anyway, you mention valves, so I assume four stroke, but sometimes people don't realise two strokes don't have valves.

[Chotu]

Sorry. It's a 4 stroke. Usa.

https://www.anchorageyamaha.com/new-...tart-25324320b

[GILow]

OK, then I am going for overheating damage which would be consistent with a hardened impeller after the outboard sat unused for a while.

I suspect the fuel was the initial problem but it is clouding the real issue. Stiff to turn over sounds a lot like overheating damage to me.

What does the oil look/smell like?

[Chotu]

Originally Posted by GILow

OK, then I am going for overheating damage which would be consistent with a hardened impeller after the outboard sat unused for a while.

I suspect the fuel was the initial problem but it is clouding the real issue. Stiff to turn over sounds a lot like overheating damage to me.

What does the oil look/smell like?

Ah... That's what I was thinking also. Overheat damage. Because it's not entirely seized.

However, the telltale is very strong. Strong as ever. But maybe the impeller isn't delivering the full rated cooling water, despite delivering the amount needed for the telltale stream to be at 100%?

Oil only has maybe an hour's run time on it tops. So it looks like absolutely brand new oil still.

[GILow]

My dad had an old Johnson 2 stroke OB that was always overheating. It was bought new and gave trouble from day one. Telltale flow was fine. It was sent back half a dozen times for new impellers. In the end they pulled it apart and found the cooling pipes in the head were full of drilling swarf.

Maybe some kind of localised blockage has caused heat damage in one area. I’d remove the cam belt and see how easily the engine turned over with the plugs out. That would tell you a lot.

[SwellGuy]

Some thoughts...

If you remove the spark plug is it still hard to rotate?

Are you in neutral? Are you sure (is the prop truly not spinning when the engine turns) ?

Is the recoil starter attached to the top cowling? If you remove that cowling and pull the recoil starter, does it operate freely? Or similarly, if you just wrap a line around the flywheel (with a knot through the notches made for this purpose) is the engine still hard to rotate?

[Peregrine1983]

I feel your pain. I bought a brand new Tohatsu 9.8 4-stroke a couple of years ago. It was NOTHING but trouble from day one. 4-5 carb rebuilds. Stalling, not starting. Just an awful and completely unreliable motor. I think new Tohatsus in particular just get ruined by the ethanol in American fuel.

I was even using solely non-ethanol in it before the last couple times I had it serviced, but it just never ran reliably. I will never buy another Tohatsu.

I now have had a 2003 4hp Mercury 4-stroke for about a year. Not sure what gas its previous owner used (probably ethanol), but I have had no problems. I use nothing but non-ethanol gas in it just to be safe.

[Shawn67]

Pull a plug, is it oily?

If you overfill the crankcase the oil will foam and get up the PCV and foul the plug(s). I had this happen with my SailPro. This can also happen if the engine is stored on the wrong side, this can make it really hard to turn over the engine if the cylinder fills with oil.

The other possibility is if the fuel pump went bad you might be leaking fuel into the crankcase. Check your oil and see if it smells of gas. You would likely also get the foaming and fouling and this could also make it difficult to pull start the engine.

Shawn

[Library70]

A friend had the same motor, gas was accumulating in the bottom cylinder after the engine sat for a while. Pull the plugs and see if anything comes out of the cylinders when you pull the cord. A bad needle valve or bowl gasket can cause the engine to flood. Also, I would disconnect the fuel line from the engine when you are not using it.

[Carver Power]

Sounds like overheating. It will run great for a little while... Pull plugs you should see signs of heat.
If it is heat damanaged I would think about a new motor good luck.

[a64pilot]

No idea, but think there is good logic in pulling the plugs and looking for liquid, plus looking to see if the plugs are bone white or wet

[GeneM]

Did you clean the carb. My Tohatsu ran well after cleaning. Look at a you tube video to do it well!

[Cpt Pat]

Originally Posted by Chotu

Like many 4 year olds, my tohatsu 8hp has been acting up.

I had some old gas that sat in it for 2 years. Marine fuel, non-ethanol, used marine Sta-bil to preserve it. The same fuel is running fine in a Honda generator as well as in Evinrude etec outboards.

However, I kept getting intermittent stalling and being unable to start the tohatsu after the stalling. It would run great for 10-15 minutes, then after hitting some chop seemed to want to stall and would run roughly, especially at low RPMs.

It did stall and strand us 4-5 times where we needed a tow.

I got new gas (all they sell at the fuel dock is ethanol garbage??). Drained the carb, had all the old gas disposed of from the tank and fuel line.

The outboard ran great for several long runs but started wanting to stall again after some high speed runs.

Here's where it gets weird!
.
It stalled out right at the boat this last time. I didn't bother looking at it and took the launch a couple times. Now, it's nearly impossible to pull start it!

I can (with tremendous force) get the engine to rotate/crank very, very slowly. Then, as it starts moving, it gets easier and easier to rotate/crank the engine. But it won't start anymore.

It's as if the engine is seized, but as I crank it, the oil lubricates it and makes it easier to crank.

To me, this can only be a seized engine or a very strange valve problem.

Any ideas on what is wrong with this very new engine???

I bought it brand new to just invest into a good outboard for once and it's really bad. I expected more than a a few dozen hours out of this thing before it had a fatal issue.

So does anyone have any ideas About what might have happened? Oil is full.

Intermittent stalling = fuel starvation. Make sure you don't have leaks in the fuel flow. These could be, in my order of likelihood: leaky hose connections at either end, bad tank vent, or inadequate fuel pressure from a bad fuel pump. Squeeze the primer bulb when the engine is acting up. Is it firm or soft? It should firm up after only one or two squeezes. Try placing the fuel tank higher than the engine carb. Does that solve the problem by providing a gravity feed of fuel? If it's a bad tank vent, leave the cap on very loosely and test. Problem solved? The newer tanks have a pressure valve in the vent so the environmentalists won't freak out from a few extra molecules of gas venting from the tank. Those valves can fail or get sticky with age. If that's the problem, replace the cap.


Hard pulling = oil leaking past the rings into the upper cylinder. You can't compress oil. If you keep trying to pull start, with incredible effort, you will eventually force the oil back through the rings into the lower engine. Test to confirm: Remove the spark plug. Put a clean white cloth loosely into the spark plug hole. Pull several times. It should be very easy to pull now (oh, by the way, put the spark plug someplace safe where the sparks won't ignite anything - or pull out the safety ring on the stop switch which shorts the magneto primary). Look at the rag. Is it oily? It shouldn't be. Are you storing the engine on the "correct" side so oil doesn't feed by gravity into the upper cylinders? Is the oil overfull?

[jim King]

I had a very similar situation on a Tohatsu 8 that came with the dingy on our chartered Leopard 44 in Belize. Same stalling out problem. We finally discovered that the kill switch was a bit loose causing the intermittent dying or stalling. Check to make sure the kill switch has enough depth to hold the kill button from stopping or stalling the engine.
On another charter we discovered the fuel line had a tear at the connection to the tank allowing air in and causing the same symptoms.

Jim