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Old 20 August 2009, 05:58   #11
Country: UK - England
Town: Dorset & Hants
Boat name: Streaker/Orange
Make: Avon/Ribcraft
Length: 4m +
Engine: 50Yam/25 Mariner
Join Date: Apr 2007
Posts: 5,551
Originally Posted by chewy View Post
I personally think it could be the Flux Capacitor, but no one seems to stock one for a mid eighties clamshell?
Thats clearly the problem - its only supposed to kick in at 88 mph - its interfering with the normal spark mid range ............

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Old 20 August 2009, 06:27   #12
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,614
...which is 76 knots (it's a boat) - no wonder it's not working!

How are they paired? Is it the low res. ones together & vice versa, or a low & a high per coil? My train of thought here is that if they are matched in resistance then you'll get equal spark on both plugs of a pair, if one of each, the lower res. lead will take more of the charge as it;s an easier path, and mean the high res. one is starved of charge...... Are your leads of a length you could swap them so the two high & the two low re. leads are hanging off the same coil?

Screw in leads sounds like a high tech version of mine. (i can replace the lead & leave the coil in place) I could be cynical and say it's on a similar theme to the Clamshell flywheel removal thread - really obscure old American thread so you can't just go out & buy a bog standard puller......

How did you check the leads - what seems OK at low voltage DC (i.e what your multimeter uses to calculate the resistance) becomes a whole different kettle of fish when you start to throw high voltage high requency AC at it. As an example when I checked the insulation resistance of my old spark plugs on the Yam were "open circuit" (i.e nothing wrong) when I prodded them with the multimeter. Then borrowed a Megger - at 1000v DC, one of them had about 150ohms insul. res. (i.e gubbed) One new set of plugs later & it was like a new engine. The same could be happening with your leads.

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Old 20 August 2009, 08:14   #13
chewy's Avatar
Country: UK - England
Town: Up Norf
Make: Avon SR4,Tremlett 23
Length: 4m +
Engine: Yam 55, Volvo 200
Join Date: Apr 2007
Posts: 5,217
True I did only use a multimeter.

I'm back at work now so its I'll see what the yard come up with?
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Old 19 April 2010, 15:26   #14
Country: Denmark
Town: Gudbjerg
Boat name: Searider
Make: AVON
Length: 4m +
Engine: 60Hp Merc. outboard
Join Date: Sep 2008
Posts: 19
Did you ever fix it? If so, what where the problem.

I have the exact same symptoms as the ones you described in the inital post.


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