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25 HP Johnson 25Raeda

M

mark_lilley

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For a while now this motor has developed a slight miss after travelling at wot for about 1 mile, which would then clear and run ok again. Of late however, it just bogs down and misfires badly. Squeezing the bulb hasn't helped. It will still idle but won't rev up, just bogs and misses. Leaving it idling for a number of minutes and then gradually increasing revs sometimes clears the issue and it runs ok again without further issue. Does this perhaps have anything to do with the thermostat signal to the powerpack at full engine temperature? Faulty powerpack? It appears to be after the same amount of running time on every occasion, by virtue of landmarks when it happens. Thank you for any help forthcoming. Mark
 
Need to check and see if the motor is overheating when this happens, remove the cowling and place your fingers in the block back by the head, if you can keep your fingers there with out burning the motor is not overheating. of course it would be better if you could take a temp reading...

OR
You can disconnect the temp sensor and see if the motor now runs right, if so it is overheating or temp sensor is bad, (REMEMBER TO REHOOK THE TEMP SENSOR)

If not over heating you need to check and see if you have spark from both spark plug wires. use a spark tester.
Let us konw.
 
Thanks for your response coueytwo. I 'fingerchecked' thetemp when this happened and could hold my fingers behind the heads for a fewseconds. Did not disconnect the temp sensor, which would be good advice. In theinterim I have pulled the flywheel, checked stator base, all coils and cleanedearths, checked pump impeller ( like new), removed cleaned and testedthermostat, cleaned temp sensor. On other advice I have checked the sparkplugs, to find one of ceramics ivory/fawn in colour while the second is muchdarker, brown/black. I assume, as I have not had further comms, that thisadvice is pointing to an ignition coil breaking down at full running temp? Iunfortunately mixed up the plugs so not sure of their original location. Also,there is evidence of raw fuel weepage past the spark plug threads on #2cylinder, which may well indicate the problem cylinder? This issue alwaysappears to happen after travelling about 1 mile at wot, as it occurs within thesame area of the same landmark. I am now contemplating changing both ignitioncoils before testing on the water again next weekend. Thanks again for yourinput. Mark
 
Ran a trial on earmuffs and the motor eventually died at slightly higher revs and wouldn't restart. Heads were still cool to the touch. Motor restarted on first pull when disconnecting the thermocouple/temp sensor and died instantly when attempting to reconnect while running. Replaced the powerpack, ignition coils and plugs, just waiting on the temp sensor, on order. Will retest and hopefully do river trial at weekend. Many thanks for the invaluable assistance, much appreciated. Mark
 
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