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Intermittent skip

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2 weeks 3 days ago #21730 by AirborneTL
Intermittent skip was created by AirborneTL
2016 912 with 130 hours. Recent annual with fuel filter, oil, and spark plugs.

Yesterday first problem ever. While warming up on a 60 degree day the power suddenly dropped from 2500 to 2000 rpm . Add to that there is a skip that happens every 5 minutes yes or so that past for 10-20 seconds before going away.

Also noticed this during power down on final. The skip caused a vibration that was gone with a power up to 3000 rpm.

I realize this is random But I'm surprised with such low hours. Any advice greatly appreciated.

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2 weeks 2 days ago #21732 by garrett
Replied by garrett on topic Intermittent skip
I would drop the float bowls and look for debris, also pull the idle jet and check for (green) corrosion.

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2 weeks 2 days ago #21738 by AirborneTL
Replied by AirborneTL on topic Intermittent skip
Checked bowls. Clean as a whistle.
Set to 4000 rpm, the rpm wandered from 3950 to 4050 and man in wandered from 23.2 to 25.2.

I also noticed one spark circuit runs rougher than the other. I did just have them replaced. Is that typical?

However, this prior underperformance was at about 40 degrees F and high humidity. Could this be a carb ice issue? How are the carbs heated?

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2 weeks 2 days ago #21739 by garrett
Replied by garrett on topic Intermittent skip
What is the gap? Make sure the center insulators did not get broken while gapping. Make sure the slide moves easily (not sticking). And last I took Roger Lee's suggestion and set my gap's to .023" which got rid of an intermittent misfire on my engine also. The carbs can be heated several ways, isn't it in your POH? What kind of aircraft's this on?

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2 weeks 2 days ago #21741 by Roger Lee
Replied by Roger Lee on topic Intermittent skip
Many times some slight rpm wander comes from the aircraft throttle setup and can be fairly normal. Yes some are pretty solid. The analog gauges don't show wander near as much as the new digital stuff on the market. They are just sensitive.
Type of plane?
This could be several things and without more info it's just a shot in the dark. Some ideas below.
What is the mag drop check doing? Normal mag drop can be 30-100 rpm and it depends if you're using an analog gauge or a sensitive digital one that reads in finer increments. . I have seen more, but not normal.
To start trouble shooting: Have you checked all the plug gaps? What is the plug gap? The NGK plugs right out of the box are gapped at .030. Gap them down if need be. Are the carbs synced? Carbs aren't normally heated. Some that have individual filters on each carb get heat from under the cowl. You aren't getting carb ice at idle or just above. You may want to unscrew each spark plug cap and trim the plug wire back about 3/8", apply a dab of dielectric grease and screw the cap back on.


Maybe as we get more info we can narrow down a cause.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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2 weeks 2 days ago #21742 by AirborneTL
Replied by AirborneTL on topic Intermittent skip
It's a 2016 TL3000 with 130 hours. Carbs are synced.

Garmin Touch Digital Display. Mag drop is 50-100

I'm certainly not a Powerplant mechanic but I thought the reason Rotax don't have manual carb heat is because they are heated full time.

She was running pretty rough on final the other day with power down. Mechanic thinks the slightly above freezing temps with high humidity a factor.

Checked bowls and did a runup today and it seems better although it still runs a little rougher on one mag compared to the other.

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2 weeks 1 day ago #21745 by Roger Lee
Replied by Roger Lee on topic Intermittent skip
With really cold temps you may be running a little lean. You could richen it one notch on the carb needle and see if that helps.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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1 week 5 days ago #21772 by AirborneTL
Replied by AirborneTL on topic Intermittent skip
I regapped to .23 no love.

I might try the needle.

Is it unrealistic to expect the individual ignition systems to run similar firing at lower rpm like 2500. One is running obviously rougher than the other.

At 4000 there is no noticeable difference between one and the other.

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1 week 5 days ago #21773 by garrett
Replied by garrett on topic Intermittent skip
Make sure none of the white heat transfer paste got on the spark plugs ends that can cause problems also unscrew plug cap and cut 1/4" off wire and resemble wire dielectric grease as Roger Lee suggested.

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1 week 3 days ago #21799 by jiott
Replied by jiott on topic Intermittent skip
For years now I have been totally confused by the use of "dielectric grease". I know it has good thermal conductivity, which is why it is recommended for heat sinks and spark plug threads, but the word "dielectric" means it is an insulator and does not conduct electricity. That being the case, why is it recommended for spark plug wire connectors and other electrical connections where it would INCREASE electrical resistance? Somebody splain to me.

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1 week 2 days ago #21800 by garrett
Replied by garrett on topic Intermittent skip
The grease stops corrosion. It is used in many applications especially in marine and industrial and if there are dis similar metals along with moisture it creates a battery effect which starts corrosion.

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1 week 2 days ago #21802 by jiott
Replied by jiott on topic Intermittent skip
Thanks for your reply, but it does not answer my question. I know grease inhibits corrosion, but why use a "dielectric grease" (insulator) where you want good electrical conductivity?

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1 week 2 days ago #21804 by garrett
Replied by garrett on topic Intermittent skip
As long as there is good metal to metal contact it preserves the connection, it just works.
Check out the Permatex dielectric grease data sheet. 441py33rout1ptjxn2lupv31-wpengine.netdna...h_docs/tds/81150.pdf

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1 week 2 days ago #21816 by jiott
Replied by jiott on topic Intermittent skip
Thanks for the data sheet. I am convinced it works because it has been used for years, and I use it myself. I just have yet to have anyone explain to me why it works. Why you would put an "insulating" grease where you want to do just the opposite. I guess I have to take it on faith.

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1 week 17 hours ago #21831 by AirborneTL
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