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Old 14 July 2014, 06:22   #1
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Merc 9.8 Two stroke missfire

Can any one help, we have missfire on Brown band 9.8 Two stroke. I have done a search but could not find any posts that may help. Have got new plugs in serviced the carb new gaskets etc. and checked float level. I suspect electrical gremmlins but dont know where to start and we dont have any testing gear. Are there any know issues with this engine, or is there any one near South Yorkshire/Sheffield that could help.
Many Thanks in advance....
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Old 14 July 2014, 18:19   #2
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How old is that engine ? What is a Brown Band. Missfires at idle, throughout the whole throttle range ? Missfires and sputters ?

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Old 15 July 2014, 05:38   #3
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Originally Posted by Locozodiac View Post
How old is that engine ? What is a Brown Band. Missfires at idle, throughout the whole throttle range ? Missfires and sputters ?

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Brown band = c 1985, missfire throughout range.
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Old 15 July 2014, 14:10   #4
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Have you tried keeping hand pressure on the primer bulb? If that cures it fit a fuel pump diaphram kit. if it dont cure it see below,is the fuel tank breather open? straight after you have run the obm, have you taken the fuel tank cap of? did it make a sucking soun d? if so check the fuel tank breather.
1/ are they the correct spark plugs?have you tried swopping the s/plugs over does the fault follow? if so it is probally the s/plug.
2/ if the s/plugs are correct, are the s/plug electrode the same colour?when removed DONT wipe the electrods
3/ if they are the same colour are they a dark or a light colour?
4/ Does the tips of the spark plugs have a glittery effect?
5/ If s/plugs have a glittery effect on the electrode do a compression test.
Please see above there is something to keep you out of mischief.
Please let me know how you get on
GENTLY pull the electrical wires coming out of the stator is one loose?
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Old 15 July 2014, 15:53   #5
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Originally Posted by uncle al View Post
Have you tried keeping hand pressure on the primer bulb? If that cures it fit a fuel pump diaphram kit. if it dont cure it see below,is the fuel tank breather open? straight after you have run the obm, have you taken the fuel tank cap of? did it make a sucking soun d? if so check the fuel tank breather.
1/ are they the correct spark plugs?have you tried swopping the s/plugs over does the fault follow? if so it is probally the s/plug.
2/ if the s/plugs are correct, are the s/plug electrode the same colour?when removed DONT wipe the electrods
3/ if they are the same colour are they a dark or a light colour?
4/ Does the tips of the spark plugs have a glittery effect?
5/ If s/plugs have a glittery effect on the electrode do a compression test.
Please see above there is something to keep you out of mischief.
Please let me know how you get on
GENTLY pull the electrical wires coming out of the stator is one loose?
Cheers Al.
I will have a go at those things next chance I get, will most likely be next week now....
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Old 15 July 2014, 18:27   #6
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Misfire on 2 strokes is often four stroking as its referred to, usually caused by misfuelling, so they fire every other stroke instead.
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Old 16 July 2014, 03:52   #7
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cptsideways, thats a good one as well, stale petrol is another.
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Old 21 July 2014, 12:08   #8
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Check the flywheel key way has not broken and the timing has moved. Seen that loads of times on that engine. You have to pull the flywheel off to check though.
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Old 22 July 2014, 04:41   #9
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Merc 9.8 Two stroke missfire

In general most 4 stroking on 2 stroke outboards is more likely when its not under much load eg when going slow or its running light in a following sea or going down stream in a river .
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Old 23 July 2014, 04:59   #10
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Sorted now guys, discovered the stator was breaking down. Turns out I was right about the electrical gremlins. many thanks for your input...
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