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Old 20-Oct-2018, 11:23 AM
maxgain maxgain is offline
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Bikes: ST4s abs
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Join Date: Oct 2018
ST4s Cutting out

Hi, I wonder if someone could throw some light on issues I have been having with my ST4s. Back in 2016 I overhauled and serviced the bike including belt change. I changed the stock plugs for iridium ones and after a lot of reading on various forums, also replaced the plug leads for some Blue Magecore ones.

After, I had a problem whereby if the bike is revved, then the instant the revs drop at their lowest point on he rev counter, if its revved again, the bike cuts out. I researched a lot of info on iridium plugs re. gap settings before I replaced these and chose to change the gap from the pre-set to 1mm. I never used the bike much since the 2016 overhaul and have have just serviced it again including replacing belts and cleaning the plugs and still have the same issue. It worked fine before I did the work back in 2016 with the original plugs/wires. I just wish to get the bike right and dont wish it cutting out when I least need it..

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Old 22-Oct-2018, 09:02 AM
Iconic944ss's Avatar
DSC Member Iconic944ss Iconic944ss is offline
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Bikes: 1993 - 944ss / Aprilia Falco / ST4S
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Hi Stu,

I'm wondering if you could have disturbed the ignition sensor on the LHS front of the bike?

Failing that, try undoing the changes you made, new components can be faulty from new, perhaps change one item at a time.

Good luck

Cheers - Frank
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Old 23-Oct-2018, 09:38 PM
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DSC Member antonye antonye is offline
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Bikes: 748S, HM1100S, DD-A
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Did you gap the plugs correctly? The gap needs to be bigger than standard plugs! You may not be getting a good enough spark.

Gap for iridium plugs should be 0.9mm, compared to 0.6mm for standard.


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