Spark plug fouling 1T

by Raymond Moran in 912 / 914 Technical Questions 7 years ago

Hello,
My 1T spark plug fouled, I replaced the the plug, checked the resistance on the cap, was OK. After five hours, the same plug is fouled. The other seven plugs are perfect, mag drop at 4000 is within 30 RPM, (3830, 3820). Any suggestions?
thank You,
Ray Moran

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Re: Spark plug fouling 1T

by Roger Lee » 7 years ago

Roger Lee

126 5.14k 4.58k

Hi Ray,

Is the plug a dry black soot? If it is this can happen during idling and or taxi time. It isn't an issue. It burns off during high rpm time.
If it's a wet oily foul then we would need to consider other things, but then it would be both plugs in that cyl.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Spark plug fouling 1T

by Raymond Moran » 7 years ago

Raymond Moran

4 9 0

Hello Roger,
It is a dry black soot, however, I experience vibration around 3200 RPM, when I replaced the plug the vibration disappeared.
Thanks for the reply.
Ray Moran

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Re: Spark plug fouling 1T

by Roger Lee » 7 years ago

Roger Lee

126 5.14k 4.58k

Dry soot does happen and once in a while you could have a bad plug. For an overall check; Make sure the plug gaps are between .023 & .027. I tend to pick .025 unless my client lives in cold country. Make sure the carbs are synced at idle and the higher rpm. Make sure the mixture screw on the bottom of the carb is turned out 1.5 turns.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Report
Re: Spark plug fouling 1T

by Raymond Moran » 7 years ago

Raymond Moran

4 9 0

Thanks Roger,
Lockwood suggests .028 on the plugs, they are all set at .028. How would .025 effect the engine? I live in central Florida.
Thanks,
Ray Moran

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Re: Spark plug fouling 1T

by Roger Lee » 7 years ago

Roger Lee

126 5.14k 4.58k

.028 is an older setting. Depending on any particular ignition system the wider the gap can weaken the spark as it tries to bridge the gap until eventually it won't perform any more. If you set a plug gap at max gap to start then it just starts to get out of spec sooner. I tend to set cold climate clients to a narrower gap. I must be getting old because I'm trying to remember the old specs, .021 - .028. Rotax changed that to .023 - .027. They must have had a reason. If you set your plugs to .025 then at the 100 hr. or annual they should not be out of spec. Since you are supposed to do the annual seeing a maximum gap of .035 just should never happen. I have seen plugs come into the shop at .035- .040. This is because people don't gap the plugs when they come out of the box. They are always too wide out of the box and people just never bother to check them for 200 plus hours. That's a sin.
Your ignition system is your engines heart beat. We don't want to neglect or disease it. It's our lifeline for staying in the air and having less pocketbook drain.
Everyone I personally know tosses plugs at 75-100 hours. For a couple bucks a piece that's cheap insurance, piece of mind and a good maint. practice.

Better to have a good strong spark that bridges the gap than one that is weak. Weak sparks just don't perform long term as well.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Report

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Spark plug fouling 1T

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