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787 RFI fouling rear spark plug

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foshow99

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I have a 2005 GTI LE-RFI that is fouling the rear spark plug every 30 - 60 minutes. I've trailered it in for repairs 4 times in the past 2 months ( twice to an independent shop and twice to the Seadoo dealership ) and haven't been able to get the problem resolved. The rectifier has been replaced again ( second rectifier in 2 years ) and the spark plug wires have been trimmed. I haven't needed to change the front spark plug yet, but have changed the rear plug several times. It starts and runs great for about 30 - 60 minutes and then it drops to 2400 RPM and will only run on the front cylinder until I change the rear plug. Does the 787 RFI have rotary valves and if so, could the rotary valve seals be the problem. Roughly how much would it cost to have it fixed ?
 
Is it oil fouled?

Yes, all 787's have rotary valves but it would be a crank seal if only the rear cylinder is doing it.

Does that cylinder fill up with oil when it sits for a few days/weeks?

Also what are the compression numbers?
 
Yes. The rear plugs have been oily. I've been cleaning them with a wire brush and starting fluid and then rechecking the gap. I haven't seen any sign of hydro lock, so I don't think that the cylinder is filling with oil when the engine is off. I changed the rear plug a week ago and after sitting for a week the Seadoo started right up and ran great for about 45 minutes before it dropped the rear cylinder. I don't have the compression numbers but, the independent shop and the Seadoo dealership both told me that the compression was fine. How does a bad crank seal lead to fouling the rear plug ? Is the oil injected with the fuel or is it fed into lubrication points without any fuel ?
 
Is it oil fouled?

Yes, all 787's have rotary valves but it would be a crank seal if only the rear cylinder is doing it.

Does that cylinder fill up with oil when it sits for a few days/weeks?

Also what are the compression numbers?


My thoughts exactly ... X2 ... Re crank seal.

Some oil is injected with the fuel through the rotary valve. However, the crank bearings are also injected in 100% oil bath. If the crank bearing seal are worn or popped out of place, that oil is drawn up through the cylinder ports - giving the symptom you describe.
 
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You can certainly check the rave valves. Easy enough to do. There is not much to taking them apart and checking-cleaning them.
 
I know this is a older thread but I'm experiencing the same issue...just curious if the source was ever found? Thanks.
 
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