Tohatsu 3.5 outboard problems

[spottydog]

My Tohatsu 3.5 2 stroke outboard has developed a problem this weekend. It will start first pull and will then run for a few minutes and then dies. after perhaps 5 or 6 pulls it will start again and runs for a further few minutes and dies again. This will repeat a number of times and then will run ok untill I get to where I am going. When I then use it again it will exhibit the same problems. Tonight I have checked the spark plug which is in good condition and the correct gap. I have checked the small fuel filter in the tank which appears to be clean and clear.
Can anyone suggest what else to check before I use it again.
The engine is only about 4 years old and was serviced about 18 months ago.

 

[rob2]

Mine is doing similar. It has been suggested that I should drain it and give it some fresh fuel - not the stuff I have stored from last season. By the way, have you kept an eye on the water tell-tale - if the waterways are blocked with salt, it may be overheating.
Rob.

 

[spottydog]

Water tell tale ok, don't think it's over heating.

 

[SimonJ]

Outboard problems

Two months ago PBO did a good article on servicing motors such as yours.
Suggest you clean the fuel system especially the carburettor jet - said to be the usual cayuse of problems (& do not use old fuel).

 

[VicS]

Set it up in a tank, wheelie bin or something. Fresh fuel as suggested if applicable. Personally I would also put in brand new plug. (you carry a spare don't you so use that).

Now get it to the point where it wont start and check the spark. Hold the lead near a bolt head or something make sure you get a spark that will jump a good bit further that just the few thou of the plug gap.

If no spark then problem in the ignition system (Check the kill button is not shorting) Coil or ignition module but not things you can test easily.

If you get a good spark but still no start then its fuel/carb related.

Good flow of fuel to carb?

Carb clean called for perhaps. Know nothing about Tommyhatsu carbs I'm afraid.

 

[charles_reed]

The description you give is definitely of fuel starvation.

You don't say if it stalls when you try and rev it (part-choked main jet).

Take the unit ashore, remove the outer casing (two machine screws each side and a pair of small screws fore and aft).

Take off the carburettor bowl and check for dirt or water residue. Thoroughly clean.

Check the needle-valve against which the float rests is moving freely (you may have to take this out by removing the axis pin for the shut-off fork). Check that carefully, use a magnifying glass, for no damage and that the minute O-ring is in position.

Test the tap allows a clear flow of fuel - frequently the centre distorts.

On the Tohatsu - I's suggest a standard spares kit of a fuel tap, raw-water impeller, as well as a spark-plug. That goes for the Mariner and Mercury derivatives, as well.

Apart from the gear-change seizing, They're utterly reliable, will do 10-15 seasons of hard work.

PS Tohatsu were the worlds' first manufacturer of outboards (in 1905) pre-dating the Americans by about 20 years.

 

[Gin]

My 15 hour old T 3.5 developed the same symptoms.

Annoyingly it would run fine in the flushing tank but not on the tender which was completely illogical I thought.

Anyway, when I dismantled the carburretor I found the needle/jet seemed clean but the bottom of the float bowl had muck in it, so I gave all the carb components a paraffin wash and using a single plastic stiff bristle from a yard broom I rodded the jet through, to be sure of clearing it and it did look as though more light was passing through afterwards, so I guess it wasn't as clean as it at first appeared.

All is now well and the engine starts and runs fine.

 

[spottydog]

Thanks Gin I will clean the carb out this week and see if that sorts it.

 

[spottydog]

Thanks for the reply Charles, the engine stalls at low revs or high revs and the time interval doesn't appear to vary very much. I had the carb bowl off last night, it all seemed pretty clean in there. So I will check the jets and valves next. The fuel tap gives a reasonable flow, although I can't say how it compares to others.

 

[PembrokeshirePromise]

Another vote for cleaning the carb - sorted similar problems on my engine.
I think mine was caused by forgetting to switch the fuel off one time - and leaving it on its side - too much petrol dried in the carb - leaving crystalline deposits.

Strip and wash in carb cleaner did the job

 

[Cliveshep]

Spottydog - your problem on the face of it is fuel starvation and the most likely cause is the float/valve assembly which periodically sticks when the chamber is full, which is why the engine performs across the rev range until the bowl is empty. You banging away pulling it is probably what causes the float or valve needle to drop allowing fuel back in. Floats and needle valves are not a user serviceable item, although you can use car brake fluid to clean the valve it is probably best to replace it. Check the float carefully, looking for slight signs of abrasion where it might hang up in the lifted position. Also leaks of course (shake it and listen) although far less likely. The only other suspect is old fuel/oil residue semi-gelled and wandering around in the main jet/jet ways, an air-line is the best tool to blow these out.

Further observation on float valve needles, on the old engines these were a solid brass taper but newer engines have a built-in fault as the seal is a minute rubber taper. Over time this progressively wears as the float pressure rams it up into the seating, eventually creating not a taper but a parallel causing the needle to stick.

 

[aslabend]

Could be the stator winding, I had a two stroke moped give similar symptoms and I spent ages cleaning carbs, fuel lines, plugs, tank, filters..... anything in the fuel system but to no avail. The bike shop just changed the stator it was fine.

 

[VicS]

Could be the stator winding

The possibility that it is an ignition system fault was why I suggested checking the spark first.

Check things that can be checked first. Tear into things when all the checks have failed to find the cause.

 

[spottydog]

Thankyou for the reply VicS, it certainly could turn out to be an electrical problem and as you say it's easier to check than the fuel side of things. That is one reason I have always preferred electrics/electronics to other aspects of engines.
Unfortunately the good wife dragged me off to the pub on getting home from work so diagnosis will have to wait untill tomorrow.

 

[alanch]

Had a similar problem with my outboard, start - run for a few minutes and die. Checked everything - plug, carb, fuel, ignition etc and it still happened. In desperation I fitted a new plug and solved problem. Have still got old plug and can find nothing wrong with it, but fit it to the outboard and problem returns.

 

[aslabend]

The possibility that it is an ignition system fault was why I suggested checking the spark first.

Check things that can be checked first. Tear into things when all the checks have failed to find the cause.

yes, but, no ....erm....... but... it was said that it runs for a time so there must be a spark. These stop start problems are a bugger, I'll shut up now...

 

[Dipper]

Try fitting a brand new spark plug even though yours appears to be working OK.

I had a simililar problem on a nearly new 2.2 Suzuki two years ago and I was absolutely convinced it was a fuel related issue. Finally, after a lot of carburettor and fuel tank cleaning (and a lot of breaking down in awkward situations) I took it to a main dealer who fitted a new plug and it has run fine ever since. Another forumite also had an outboard with the same erratic behaviour. When I posted my solution, he changed his plug for a new one and cured the problem instantly.

If it isn't the plug, you will have a spare to add to your tool kit.

 

[richardm47]

The air valve on the filler cap isn't letting enough air in, so after short time running a vacuum forms in the tank, and enough petrol can't get out of the tank into the carb. This happens on mine. So I run it with the main filler cap loosened. A new filler cap / air vent assembly costs over £20!