www.iFourWinns.com

Hi folks.
I wonder if anyone has any ideas how to solve my 5.7gs Volvo Penta's lumpy running?
It seems to dislike the 6 knot 40 minute slog back to the pontoon. Having run fine at 20kts for an hour, when limited to 6kts it eventually starts to bog down, sounding like it's missing one or two cylinders until it's revved in neutral to around 2/3k revs, when it'll clear for a while.
The plugs are new. When it's ticking over, I can remove any of the left bank's plug caps and it makes no difference to how it runs (though I can hear the spark jumping from plug cap to the plug when I move it closer). If I remove a lead from the right bank, it makes it run rough straight away. On open water it'll do 24kts (there's 1.5 years of muck on the bottom), so it's OK at higher speeds.
Could the cap be bad?
Any advice gratefully received!

Could be the cap, rotor, or the high tension leads themselves. When was the last time this boat had a full time up?

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Thanks for your reply. I'm going to try and find another cap. I did get some new leads, but for a different V8. Unfortunately, that meant most of them were too short, so I have so far only been able to change those I believed to be suspect. Time to do some shopping. Trouble is, here in the UK just a cap and leads is around $200 with me fitting it, so I've been reluctant to just throw money at it.

Look at the contacts inside the cap. If there is just light corrosion you can clean that up with some fine sandpaper but if it's heavily corroded it and the rotor should be replaced. The plug wires can be tested with an ohm meter. Resistance should not be more than 1000 Ohms per foot of length.
My experience is that the wires rarely go bad but the cap & rotor will have corrosion on the contacts if the boat was used in a salt water environment.
Then look at the plugs. I usually replace them every other season.
Too bad you get robbed on GM small block parts there. They are dirt cheap to repair here. The ones you get robbed on here are modern outboard parts. They don't need as much maintenance by far but the cost of parts is criminal!

_________________
88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II