Fouling the rear plug

[rsmi86]

I have a 1998 GTX RFI that has a SBT engine in it that after about a hour of running will foul out the rear plug. I can switch the plugs and run for about another hour or so then the rear fouls out again. I’m using the OEM NGK plugs gapped at .025. I’ve ran a compression test and have 150 in the front and 146 in the rear. Using a spark tester both look as if there firing ok. New gas in the tank and I don’t premix. The plug is gas fouled. It doesn’t die and if I shut it off it will restart..but until I change the plug it will only have around 3500 rpms. If it was a car I would say it need a coil but not for sure on this rotax engine. Any suggestions

[SBT-Tech 3]

Re: Fouling the rear plug

You can only get 3500 RPMS after you change the plug, or before you change the plug? What is your rpms in and out of the water at idle?

[rsmi86]

Re: Fouling the rear plug

Before I change it after around 6800 rpms. It idles around 1500 to 1800 in water or out.

[rsmi86]

Re: Fouling the rear plug

With 2 new plugs in it you couldn’t ask for a better running engine.

[rsmi86]

Re: Fouling the rear plug

Might seem to foul quicker if I ride some then park up and swim some.

[SBT-Tech 3]

Re: Fouling the rear plug

Idle RPM should be 1500 rpms in water, and 3000 rpms out of water. It sounds to me like you have an injector leaking. I would have your injectors looked at, as well as your fuel pressure.

[SBT-Tech 3]

Re: Fouling the rear plug

Also, these RFI ski's idle only on one cylinder. It's part of the emission control from the computer. The computer will also switch which cylinder idles, to prevent plugs from fouling.

[rsmi86]

Re: Fouling the rear plug

Ok then I’m going to switch the injectors around and see if my problem follows. If it does follow than I’ll need to replace a injector, but if it don’t and I still foul the rear plug it starting to sound like I might have a ECM or injector control module problem. I’ll also check fuel pressure. I’ve downloaded the shop repair and parts manuals from sea doo there good for tear down but have limited theories and description and no diagnostic in them.

[rsmi86]

Re: Fouling the rear plug

I have solved my fouling problem....I think....wasn’t getting enough air, opened the breather lid a little and ran ok. Before I took the lid loose I fouled three plugs in a 8 mile stretch of water. After I lossen it I ran another 15 to 20 miles on a set of plugs that I fouled out earlier. Now I have another problem, wide open maxed out I can only get 6200 rpms and about 48 mph with a gps speed’o...