Rough Running New Rotax Engine

[ackselle]

The ROTAX Heavy Maintenance manual, Section 74, has all the wiring diagrams.... which are slightly different depending on the serial number of the engine. It also has some basic troubleshooting techniques for the ROTAX CDI Ignition. All the manuals are available at no charge at ROTAX-Owner.com.

[SWeidemann]

Today I had sudden onset rough running in my 115 hour 912ULS powered Kitfox Vixen (with Ivo three blade ground adjustable Ultralight prop). Mag checks were okay, temps all around seemed okay however there was a decidedly very rough mode. I made a precautionary landing at the nearest airport (after considering I may have to come down wherever necessary). Propeller looked okay, I took off top cowl to look for signs of what it may be. Could find nothing out of the ordinary. In the meantime a RV 6 pilot showed up & parked next to me. Turns out he also had a Kitfox Model 4 back home with an 80 hp Rotax 912, so he was very interested and helpful. The reason for his stopping at this airport was to have supper with an old friend (arriving in a car). His friend showed up and the three of us looked & discussed ideas (plugs, CDI failure, bad ground, contaminated fuel, carbs suddenly out of synch, fractured carb boots?). My new RV/Kitfox friends friend noticed that one of the three stainless steel leading edge tapes was missing. We were guessing this may have caused an out of balance situation, I peeled off the other two leading edge tapes and did another runup. Things were much better vibration-wise, so I did a lap around the pattern and flew home with things running just fine. Now, to clean up the blades and put some tape back on. My RV friend had been more than willing to fly me home (about an hour’s trip). What a guy.

[DesertFox4]

Skot, glad someone notice the missing tape on the prop. Good news that your new engine is healthy.

I’ve had one of those stainless tapes slide down a blade on my Ivo prop just a 1/2” or less and it made a sound just like a major exhaust leak in the engine. A little unnerving when it happened but like yours, all my engine instruments said everything was within normal operating paramiters. I landed and quickly saw the issue. I then removed the stainless tapes on all 3 blades (not real easy to do) and soon replaced them with a black vinyl type prop leading edge tape. That stuff never slid at all. It would get rock chips eaiser but stayed put and looked better.

[Wheels]

ackselle has the money. The section he is referring to has all the diagrams. Just make sure you don't get confused by the references to 914 or older style CDI packages. I saw a rant a few years back about how confusing the chapter was. Its not that its confusing, its that it is information rich. It deals with ALL the different engines. just find yours, read, fix.

[jdmcbean]

From experience.. always check ignitions at the 4000 rpm recommendation.
Lower Rpm settings will sometimes run rough. Be sure to get the engine to operating temps..
Also, do not be fooled by thinking carbs will not mask themselves as ignition.
Be sure to do a manual sync... Then a pneumatic sync. Be sure the choke is returning.. sometimes the choke cable will get caught.
Don't assume.. Check the obvious first.
Personally we have chased ignition issues only to learn we had needle clip position wrong ok no a carb rebuild.

[Wheels]

OK, now John has the money.
If you didn't do the pneumatic sync, you didn't actually set yourself up for success. Do that. Rotax owner.com has all the video tutorial you will ever need.

[aviator79]

OK, now John has the money.

He definitely has plenty of mine!
(And worth every penny.)

[efwd]

Wow. John is monitoring this forum in the middle of Airventure! I love that. Must be tired though.

[Dorsal]

From experience.. always check ignitions at the 4000 rpm recommendation.
Lower Rpm settings will sometimes run rough. Be sure to get the engine to operating temps..
Also, do not be fooled by thinking carbs will not mask themselves as ignition.
Be sure to do a manual sync... Then a pneumatic sync. Be sure the choke is returning.. sometimes the choke cable will get caught.
Don't assume.. Check the obvious first.
Personally we have chased ignition issues only to learn we had needle clip position wrong ok no a carb rebuild.

Had this problem, had me scratching my head for a bit.