Tohatsu 3.5 2 stroke problems

stuartwineberg

stuartwineberg

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Here's the story

Decreasing amounts of water from piddle tube but always starts second pull. This years fuel mix - approx 50:1
One day works fine for 20 mins and then refuses to start from warm. Cleaned out the carb - no change. Off to service centre. New impeller, waterways cleaned out. Test run fine in tank.

Next time out - 20 mins fine, loads of water from piddle tube. Then wont start from warm

Now wont fire at all. Not the kill switch - have disconnected it. Fuel getting to the plug - its wet when I take it out. Some sort of a spark when tested against the block although not what I would call "fat". I suspect compression or HT - what do you all think and what to do?
 
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stuartwineberg said:
Here's the story

Decreasing amounts of water from piddle tube but always starts second pull. This years fuel mix - approx 50:1
One day works fine for 20 mins and then refuses to start from warm. Cleaned out the carb - no change. Off to service centre. New impeller, waterways cleaned out. Test run fine in tank.

Next time out - 20 mins fine, loads of water from piddle tube. Then wont start from warm

Now wont fire at all. Not the kill switch - have disconnected it. Fuel getting to the plug - its wet when I take it out. Some sort of a spark when tested against the block although not what I would call "fat". I suspect compression or HT - what do you all think and what to do?
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If the plug is very wet and not the result of over choking i'd suspect that the carb might be flooding but have you tried a new plug?

You should be able to draw a spark best part of a cm. Testing by holding the plug aginst the block is not good enough

If you think the compression is bad check it. I dont suppose you will find a specified figure but I'd accept anything over 80psi.
 
stuartwineberg said:
Here's the story

Decreasing amounts of water from piddle tube but always starts second pull. This years fuel mix - approx 50:1
One day works fine for 20 mins and then refuses to start from warm. Cleaned out the carb - no change. Off to service centre. New impeller, waterways cleaned out. Test run fine in tank.

Next time out - 20 mins fine, loads of water from piddle tube. Then wont start from warm

Now wont fire at all. Not the kill switch - have disconnected it. Fuel getting to the plug - its wet when I take it out. Some sort of a spark when tested against the block although not what I would call "fat". I suspect compression or HT - what do you all think and what to do?
Click to expand...

I have two of these engines, one Mercury-badged, one Tohatsu. The spark always appears weedy but if the carb is clean and fuel reasonably fresh it always starts adequately: usually second pull except after long storage. Took the Tohatsu out of the cellar yesterday after a winter there and it took about five pulls to start, and misfired for maybe ten seconds before working properly. It was on last years fuel but did have "fuel stabiliser" in the last tankful last year.

I used to disbelieve stories about petrol in sealed cans "going off" but this new ethanol-polluted muck we get now is horrible. Apart from going "off" it corrodes alloy carb parts.

If these engines are running fine I leave the carbs alone, but a very thorough strip and carb clean is always the first thing to do if a problem. Also check the tiny filter in the top of the fuel tap is clean.
 
The similar problems I have had with my 3.5 have always been to do with the float chamber fuel level. Once with gung that was stopping the float settling down to the correct level and once when the little needle valve had corroded away to very little. You need to take off the float bowl off and look what is going on there. It could of course be ignition but my spark has always looked a bit weedy but starts first time.
 
A 50:1 mix for Mercury/Tohatsu 2 strokes is normally the "running in" mix. I have a 2.5hp mercury 2 stroke and use 100:1 after the run in period - same on a Yamaha 8hp 2 stroke which is what both makers recommend. This might not be the cause of your problem but may help keep the plug cleaner.
 
coveman said:
A 50:1 mix for Mercury/Tohatsu 2 strokes is normally the "running in" mix. I have a 2.5hp mercury 2 stroke and use 100:1 after the run in period - same on a Yamaha 8hp 2 stroke which is what both makers recommend. This might not be the cause of your problem but may help keep the plug cleaner.
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The recommended fuel mix is 50:1 ( 25: 1 during the break in period)

( The same for Mercury according to the on line owners manuals)

The best mix for most 100: 1 motors is also 50:1 It is usually specified when used commercially.
 
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Seeing this thread reminded me on need to clean my carb on small 3.3 Mercury however before I do is there a source of info on removal I should be reading? Lots of vids on cleaning but just thought there might be some info on actual removal. Changing the plug and purring in new clean fuel doesn't seem to have worked btw. Is the manual only source a research material ?
 
ashtead said:
Seeing this thread reminded me on need to clean my carb on small 3.3 Mercury however before I do is there a source of info on removal I should be reading? Lots of vids on cleaning but just thought there might be some info on actual removal. Changing the plug and purring in new clean fuel doesn't seem to have worked btw. Is the manual only source a research material ?
Click to expand...

Removing the carb off a 3.5 is fairly basic stuff. You don't need a manual or video. Take the engine covers off and you will see how it comes apart.
 
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ashtead said:
Seeing this thread reminded me on need to clean my carb on small 3.3 Mercury however before I do is there a source of info on removal I should be reading? Lots of vids on cleaning but just thought there might be some info on actual removal. Changing the plug and purring in new clean fuel doesn't seem to have worked btw. Is the manual only source a research material ?
Click to expand...

Pretty simple stuff.

Work where you can find any little bits you drop. Take note of how each part is fitted as you remove it and where any springs washers or spacers fit.

The service manual at http://162.144.28.33/lib/mercury/manuals/22-25-3-33.html#/0 should tell you all you need to know beyond what is covered by your owners manual.
 
Greeny many thanks this looks like it might be just the thing for me to start with. The cleaning the carb part is easy having had some car experience on carbs but have zero outboard knowledge. Having had it serviced by outboard co a couple of years ago not prepared to waste more on that route so DIY is only option now
 
ashtead said:
Greeny many thanks this looks like it might be just the thing for me to start with. The cleaning the carb part is easy having had some car experience on carbs but have zero outboard knowledge. Having had it serviced by outboard co a couple of years ago not prepared to waste more on that route so DIY is only option now
Click to expand...

No problem. It really is easy if you take your time. Good bit of advice from Vic. Do it somewhere where the bits you drop can be found easily. On the back rail is not a good place. Spread a cloth on the floor below it then the bits you drop don't bounce away, they sit where they fall.
 
VicS many thanks it's currently in the garage so yes can put down something under it prior to removal . I am hopeful given the service the bits undo as seems well greased around fuel pipe and bolt where it attaches . I am hoping that cleaning the carb will address issues based on what I've read .
 
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