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Old 06 September 2014, 10:20   #1
nob
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merc 50 wont rev fully at wot

This is driving me mental! I have a 1994 merc 50 hp 3 cylinder 2 stroke which starts brilliantly, idles well, runs fine upto half throttle then wont rev anymore at wot. I've done all the usual checks with fuel and cleaned carbs, new plugs, but no 2 plug is always wet and oily after i've tried wot, any ideas? Last time out it started off running slow at wot then intermitently jumped into life a few times before running perfect for about half hour before it went back to low power at wot and stayed like it. I'm thinking its electrical because the plug is oiling and getting wet. Its on a 4mtr searider . Any ideas would be greatly appreciated, cheers, nob
Almost forgot, does this motor have an oil or overheat alarm if so where is it?
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Old 06 September 2014, 11:43   #2
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Hi

Have you tried changing the coils around could be worth a try.
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Old 06 September 2014, 12:04   #3
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Hi dave, do you mean the coils the ht leads plug into or coils up in the stator?. I have put a 2nd hand replacement coil on the no2 ht lead but havent had time to test and i'm not feeling particularly positive!. Im going to test tomorrow so fingers crossed! Cheersfor the input, at least im going down the right route.
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Old 06 September 2014, 12:18   #4
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Quote:
Originally Posted by nob View Post
Hi dave, do you mean the coils the ht leads plug into or coils up in the stator?. I have put a 2nd hand replacement coil on the no2 ht lead but havent had time to test and i'm not feeling particularly positive!. Im going to test tomorrow so fingers crossed! Cheersfor the input, at least im going down the right route.
Hi nob

Yes HT lead coil, what about HT leads, do you own or could aquire a multi metre.Also Ht lead coil end check that it is opened with a good contact on your coil had this problem with mine, the conector was closing make for a bad contact, also bad plugs worth checking or change around see if problem moves.
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Old 06 September 2014, 13:09   #5
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Hi dave, i did put new leads on with the new plugs so if it wont run right tomorrow i'll try swapping plugs and leads round as i know you can sometimes have faulty new plugs. I do have a meter but what would i be testing because it would be difficult to test spark out put or anything else at wot, many thanks, nob
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Old 07 September 2014, 14:17   #6
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Well, thats it, im at wits end, tested today and it ran even worse! Miss firing and vibrating, dont know what to do next so i'll put the original coil back on and hopefully it will be as it was and then start scratching my head!
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Old 07 September 2014, 15:23   #7
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Timing out?
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Old 07 September 2014, 15:26   #8
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I don't know if it's a similar system but one of the magnets on my V6 Mariner flywheel came loose (evidently common on this model) and produced similar symptoms. On mine they're only glued on & I count myself lucky that it didn't smash my stator!!
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Old 07 September 2014, 15:52   #9
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Thanks spartacus and paddlers, i'm not sure about the timing because sometimes it will suddenly spark into life intermitently, but i'll check it anyway just in case, did your magnets come off paddlers or just become wobbly, and can you see or feel them without removing the flywheel? I think tomorrow i'll swap round carbs, coils, plugs etc to see if i can make the problem move to another cylinder, oh, and also compression test, fingers crossed i'll find something. Many thanks for the input guys as i'm getting tunnel vision so any ideas are good ones, cheers, nob
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Old 07 September 2014, 16:09   #10
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Tough to see initially. A bit of magnet fell off and I saw it below the flywheel. It wasn't until I got the thing off I could see that one had disintegrated and shifted. Needed a Mercury flywheel puller to get it off and 50 found me a second hand flywheel. All sorted. Symptoms with mine, bit of a lottery starting, idled well revved up to 4200 rpm fine. Did the usual, new plugs,drained carbs etc. I'd already put new plug leads on last year. Normal WOT 5500 rpm is now back !!!
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Old 07 September 2014, 16:41   #11
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Awesome paddlers, good job. Weird thing is mine starts lnstantly, idles great, runs nicely up to 1/2 to 3/4 throttle but does nothing more at wot, then sometimes, and not very often, it will suddenly jump up to full revs then die back again a couple of times then go flat again!
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Old 12 September 2014, 16:51   #12
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Did you check compression? You obviously have an ignition problem of some variety (always check the ground connections), but could be a combination of issues.
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Old 12 September 2014, 17:08   #13
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Awesome paddlers, good job. Weird thing is mine starts lnstantly, idles great, runs nicely up to 1/2 to 3/4 throttle but does nothing more at wot, then sometimes, and not very often, it will suddenly jump up to full revs then die back again a couple of times then go flat again!
That's either carburetion or electrical, depending on quite how suddenly on-off the sudden full RPM is.
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Old 13 September 2014, 02:13   #14
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do an electric check, it could be the high speed bobbin on your stator if it is it will mean a new stator, have you checked all the earths are clean bright and tight?
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