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Old 04 July 2015, 19:09   #1
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2 stroke starting and white smoke.

This may be coincidence, but since I had a guy service my Tohatsu M40c this is occurring...

Difficult to start...turns but won't fire. Eventually starts and runs perfect, idles steady too after few secs warming up on free throttle. No noticeable misfiring or rough running.

If switched off again its 50/50. Sometimes starts on button, sometimes difficult again.

I do this...close vent, prime till bulb is firm, open vent, choke and turn key.

Inline fuel filter (after the clear bowl filter) only fills half full before primer bulb is firm. If doesn't start have to repeat priming each time.

Also, immediately upon start up, big plume of white smoke. Definitely smoke. Then clears after few seconds. If left for a bit then started again, another plume of white smoke.

Engine has exceptional compression 130 exactly on both cylinders.

Spark plugs are good.

New fuel with some cleaner added 50:1 mix.

Fuel pump is squirting fuel.

Battery is strong.

Started replacing fuel lines as noticed that tiny black bits accumulating in the clear filter bowl even after a few pumps after cleaning out. Fuel can is clean, no cracks or splits in fuel lines but maybe perished inside?

Intend to whip carb out for a clean tomorrow as think it may have sat with old fuel for a bit.

Does this sound like just a carb clean required or are there other possibilities?

Some have told me the white smoke is normal and fine if its clearing in few secs and as long as its not steam. Others say may be water in fuel. But its fresh fuel.

Anything else I should check?
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Old 04 July 2015, 20:28   #2
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Why close the vent? It's there to prevent a vacuum as fuel is used. I only closed it to prevent rainwater getting in.

Hopefully you don't choke on restart; if so, that may be part of your problem. I used to close the choke until the motor fired briefly, then opened it. Had to sit off for several hours before it needed choke again (That was a Honda 40; I don't know about now, as my F115 has a mostly auto choke.)

If you absolutely have to pump the primer bulb every time you start, that kind of points to another problem: weak fuel pump? leak in the fuel lines? Only time I pump the bulb (on my F115 or on my old Honda 40) was when it had been sitting for a couple weeks or more.

jky
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Old 05 July 2015, 02:50   #3
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Double-check the butterfly choke valve actually opens. (Located behind the air box on top cylinder). It's known to seize. Lightly lube spring with a little marine grease. The solenoid should click when it's opened, etc.

Next, drain the carb fuel bowls. Any contamination, then think about a carb strip down. Also check the inline fuel filter. I'd also consider replacing the primer bulb as these can fail with age. Quicksilver versions, although a little pricey are good. No need to close vent on fuel tank, keep open.

The sparkplugs, are they genuine NGK part? Also check they are gapped properly, and the HT leads sit snug on top.
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Old 05 July 2015, 05:26   #4
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Ht leads in good shape, spark plugs proper ngk, valve is all good, inline filter just renewed, primer bulb - don't know how old but seems to be ok. Bit will probably replace all lines.

Sorry should have pointed out - yes only choking on first fire up.

Do keep the vent open.

Thanks for the help and advice.

I'm going to strip carb today as thats the only thing I can think of now, although it ticks over and behaves perfectly once running.

Have to be after I watch the tall ships leave today though!
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Old 05 July 2015, 05:38   #5
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White smoke from an engine is usually water vapour... either when weather is very cold for the first few minutes of running... or a water leak of some kind into the cylinders.
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Old 05 July 2015, 12:48   #6
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Pretty warm temps at moment so doubt its that. Hopefully not water getting into cylinders although compression is very good and even.

After heading out to see the tall ships off, came back, stripped and cleaned carb. Seemed fairly spotless except for flat valve which has a lot of crud in it. Now just to stick it back in and see if its made a difference.

After that the only thing remaining I the fuel lines as the fuel pump is squirting plenty.

For the life of me cant find anyone local who stocks the skinny fuel line for the bits under the hood. Cant get tank to engine fuel line aplenty.
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Old 05 July 2015, 13:27   #7
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>>> cant find anyone local who stocks the skinny fuel line for the bits under the hood.

Just replaced all the rubber lines on my 15hp. Garden machinery suppliers had pretty well every size down to the tiny hoses.... motor factors had the slightly larger ones.

Boat shop wanted to sell fuel hose priced off a Mercury dealer-only website per 100mm.... but it was obviously generic pipe on a coil bought in bulk.
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Old 05 July 2015, 15:41   #8
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Ah yes...that's exactly who I need to see!!!
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Old 05 July 2015, 15:48   #9
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Fresh fuel can have water in it.

What sort of cleaner have you put in the fuel, and was the white smoke there BEFORE the cleaner?
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Old 05 July 2015, 15:57   #10
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No the white smoke has literally started immediately after it being serviced by the guy. Its literally just a plume on startup then clears. Just a bit of Lucas complete fuel clean for carbureted engines. Used this for a long time and its very good without being harsh.

Going to use some fresh fuel tomorrow after refitting the cleaned carb and new lines. Will see what it does.
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