tohatsu 3.5

Seastoke

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so went ashore on the dingy yesterday , engine has been running fine went to start it again , no firing so rowed back . so we have got spark new fuel any ideas welcome , pulled carb bits all looks fine . HELP
 

VicS

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I agree try a new plug but how good is the spark? It should be good enough to jump an air gap of about 10mm.

Fuel flow OK? Filter clear? Tank vent open and unobstructed ?

2 stroke or 4 stroke ? Some of the jets in 4 stroke carbs are very tiny and easily blocked.

If you can steal a compression gauge do a compression test.

If plug is excessively wet with fuel it may be flooding.
 

Seastoke

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I agree try a new plug but how good is the spark? It should be good enough to jump an air gap of about 10mm.

Fuel flow OK? Filter clear? Tank vent open and unobstructed ?

2 stroke or 4 stroke ? Some of the jets in 4 stroke carbs are very tiny and easily blocked.

If you can steal a compression gauge do a compression test.

If plug is excessively wet with fuel it may be flooding.
vents on tank fine plug not soaking , i will have to buy a plug and 2 stroke. i dont see a filter
 

VicS

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vents on tank fine plug not soaking , i will have to buy a plug and 2 stroke. i dont see a filter
ITYWF that its part of the fuel tap, sticking up inside an integral tank, or its on the bottom of the pick up tube inside a remote tank
 

forelle541

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There is a filter inside the tank that should be attached to the tap, they can fall off, ours did and picked up a bit of the cap inner seal that had ripped away. Running well now.
 

coopec

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I agree try a new plug but how good is the spark? It should be good enough to jump an air gap of about 10mm.

Surely a typo?

NOTE. Yes it is a typo. Just read a post on another thread by VicS
At a first guess I'd say NGK BP6HS, or the suppressed version BPR6HS gapped at 0.040" ( 1.0mm)
or one of the pre-gapped ones BP6HS-10 BPR6HS-10. (-10 indicates that it is supplied gapped to 1.0mm)
 
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VicS

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Surely a typo?

NOTE. Yes it is a typo. Just read a post on another thread by VicS
At a first guess I'd say NGK BP6HS, or the suppressed version BPR6HS gapped at 0.040" ( 1.0mm)
or one of the pre-gapped ones BP6HS-10 BPR6HS-10. (-10 indicates that it is supplied gapped to 1.0mm)

No it is not a typo
A CD ignition should be able to produce a spark which will jump at least 10mm in free air. It is the gap specified to set the type of adjustable gap tester illustrated below. ( 7/16" is the figure you will find quoted on the American specialist outboard engine forums, but 5/16" for points ignition)) This ensures that under compression conditions in a running engine you will get a good powerful spark between the plug electrodes.

Holding a spark plug against the engine and observing the spark between the electrodes is a hopelessly inadequate method of testing an ignition system if you are troubleshooting

ET96019.jpg
 
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Zagato

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Had problems with both my Tohatsu 3.5 and Marina 6 carbs, not uncommon apparently, if it is not to old they will replace carb happily. Mine were both out of warranty but replaced. It is not always just the fuel that goes off!! Looking forward to going electric for the tender...
 

Skylark

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I have a Tohatsu 2.5 2-stroke which must by now be 15 years old and probably done less than 10 hours running. It misbehaved a couple of years ago and a new plug solved the problem. Don't really understand how they can fail/breakdown but that appears to be what they do.
 

Elemental

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I would almost guarantee it's a fuel issue. The carbs on these motors seem very prone to clogging. I would strip the card off the engine, pull everything apart end wash in carb cleaner. Perhaps consider a carburettor refurb kit. I had persistent starting issues for a number of seasons. Since I renovated cleaned the carb on my 3.5, it starts pretty much first pull - even after weeks of disuse and sitting on the pushpit.
 

Seastoke

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So guys update , got a new plug today £4. She fired first time , run hot then she started again so , result thanks for input guys. SS
 

jwilson

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For anyone else reading this, don't expect a huge 10mm gap spark from even a perfectly functioning near new Tohatsu/Mariner/Mercury 2.5 or 3.3/3.5 with a brand new correct NGK plug. Usually the spark is pretty feeble, barely visible in daylight, but if the carb is 100% clean and the fuel is OK the engine will work fine. I am on my third of these engines, almost always any problem is fuel or carb related. Though I usually try a new plug as a quick fix. Doesn't very often actually fix it, but particularly with a boat afloat it's a lot easier and less messy than removing and cleaning the carburettor. It does as you have found out sometimes work, even with an old plug that looks OK. And less chance of dropping tiny parts overboard.
 
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