carbon build up

by Frank Barker in 912 / 914 Technical Questions 6 years ago

NEW 912 ULS.
Large carbon build up on exhaust. Burning rich. Less then 40 hrs. Carbs balanced. New exhaust system. Thoughts?

Re: carbon build up

by Rotax-Owner » 6 years ago

Rotax-Owner

5 607 1.94k

Hello

Can you upload some photo's so we can see the amount of carbon build up?

Thank you!

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Re: carbon build up

by Roger Lee » 6 years ago

Roger Lee

125 5.12k 4.52k

If you have been idling a lot that forms a dry black sooty carbon. If you have your plug gaps too wide it can cause poor burning. If the carbs aren't synced that can cause a rich mixture. If the mixture screw on the bottom of the carb isn't adjusted correctly (1.5 turns out) it can cause more carbon build up.

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

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Re: carbon build up

by Frank Barker » 6 years ago

Frank Barker

6 8 6

Thanks Roger.
Factory NEW @ now 24.4 hrs. ROTAX muffler system would NOT fit into Bed Mount. A convoluted system designed by race car manufactor to fit. Could this have an impact? Would suggest plugs et al from Austria should be good as a result of bench run...still exploring. Will again have carbs adjusted. Low rpm (1800) now reading (2200) now!

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Re: carbon build up

by Roger Lee » 6 years ago

Roger Lee

125 5.12k 4.52k

Even though it is new you need to check some things. This engine may have the new Rotax spark plugs and if that's the case no adjustment is necessary. I would however pull the plugs and check them. I have seen several where the porcelain turned inside the plug body. Just inspect them. Stranger things have happened. Make sure if it has the NGK plugs gaps are between .023 - .027. .025 is good, it's in the middle. :) . If the engine is idling a lot then you will see more dry black soot on plugs and in the exhaust. Don't be afraid to go run the engine normally at higher rpms. Don't sit and idle at low rpms. If you are just sitting on the ground and warming up then 2K or higher. Low rpm is fine when it comes to shut the engine down. You could set the low rpm for 1650 - 1700 so long as you know not to sit and idle there. Many set the idle lower for landing approaches and shutting the engine down and to keep from riding their brakes constantly.
The carbs ABSOLUTELY need to be synced on a new engine and especially at the 25 hr. mark. Things settle in and cables relax. I don't know what kind of exhaust system you have, but yes it can have an impact.My guess this is something simple that just needs some attention as a new engine and not a real engine problem.

Side note:
You have right at 25 hrs. and you are now REQUIRED to do the 25 hr. inspection if you want your warranty and make sure that engine is registered. Make sure the 25 hr. inspection is in the logbook. It is very important. If you have a problem during the warranty period Rotax will want a copy of your logbook. It had better be in there along with the other prescribed maint. along the way. I usually take the inspection checklist out of the Line Maint. manual. Write on the front it is for the 25 hr. and fill in the front page. I use that as a good platform to do my inspection. There are of course a few items on that list that are for the annual / 100 hr., but that's okay. Just write N/A. Annotate in the margins anything you do. If you change oil and filter write it down. If you check the torque on the engine mounts write it down and at what torque number. Checking all the hoses for leaks. Sign off each item that applies and you check. At each entry on the list write no leaks found for hoses. If something is loose just write down you torqued it to whatever the spec is. Make it thorough and complete. It won't hurt a bit and this will help develop good maint. practices while you own the plane, keep its value up, help if ever there is an incident and Rotax, the FAA, an insurance carrier or civil litigation ever happens. Hole punch your checklist and keep it in a 3 ring binder. For all future inspections do the same thing. Print out a checklist for the fuselage part to and use these each inspection.
Don't strive to be at the bottom 5% as an owner or mechanic. Strive for the top 10%. It's just as easy, safer and protects you and others.

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

Thank you said by: RotaxOwner Admin

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carbon build up

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