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Old 19 July 2009, 15:53   #1
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Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: reiver 3.8/regal3760
Length: 10m +
Engine: 40hp 2st 2x6lp 315
Join Date: Jul 2009
Posts: 1,494
yam 40 3cyl 2 stroke idle on 2 or 3 cylinders

just got me little rib out of the garage and fired it up for the firtst time this year & it seemed a bit lumpy on tickover did the usual checks swaped plugs about but couldnt get it to run on 3 no spark at no 1 cyl eventualy discovered when you advance the throttle you get a spark on all 3 & i seem to remember someone telling me about a suzuki that ran on 2 untill you open the throttle then went on to 3 is this the case with the yamaha or do i have a problem? it always seemed to be a bit erratic on tickover but i never got round to investigateing before

engine is 2001 3 cyl 2 stroke

cheers
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Old 20 July 2009, 05:21   #2
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Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,610
Welcome to ribnet!

I can't say for sure here without more digging to check your engine, but I doubt it unless you are fuel injected. If you just killed the spark on one cyl of a traditional 2- stroke it would still ingest fuel whether it's sparking or not, & so oil itself up. Also as you point out without a pressure relief on the cyl it gets quite lumpy! Killing cyls at idle is OJK if you have a multi cylinder fuel injected machine, but hightly unlikely on a 3 -pot. (this is where a raft of people will be along to prove me wrong!)

Best thing to do is to swap plugs, coils & HT leads (assuming they're not all integral) around one at a time & see if the problem follows the plugs or the coils. My old Yam ran like a dog at idle - cured with a new set of plugs. (I later meggered the plugs - one was part shorting)
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Old 20 July 2009, 16:44   #3
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Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: reiver 3.8/regal3760
Length: 10m +
Engine: 40hp 2st 2x6lp 315
Join Date: Jul 2009
Posts: 1,494
cheers but i tried swaping plugs and coil but fault stayed on top cyl(if it is a fault) got the engine warmed up today still on hosepipe and once up to temp it idled ok (not brilliant but acceptible) once you open the throttle the leaver on the side of the cdi unit moves full deflection and you get 3 cylinders return to idle and back to 2 cylinders again (definately ignition as no spark) realy need someone with the same engine to check theres by taking off no 1 plug lead at idle

engine has probably been like this for 3 years i've owned it & i never susspected anything was amiss just thought maybe idle jets needed a tweek

very strange
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