Rough Running New Rotax Engine

[Ak360]

Hoping someone out there may be able to help.

I just completed my kitfox's first runup and noticed that the engine is running very rough when I did my mag check on one of the mags.


When I did my mag check, "B" runs perfectly smooth with a slight RPM drop, but "A" runs very rough with a significant RPM drop.

I can't seem to find the cause of the problem.

In case it helps, the check was done at low RPMs simply as a preliminary check.

[Slyfox]

bad spark plug or wire or two wires crossed.

[DesertFox4]

Did you sync the carbs yet? Do you know the syncing procedure? This is critical to getting both halves of the engine working in unison.

Check that both "chokes" are returning to their full off position and not sticking open.
Don't panic. Odds are it is a minor issue and not a bad ignition module.

[Ak360]

Chokes are good. Not familiar with carb sync, but that should be separate issue to the ingnition roughness. The carbs serve each half of the engine where the ignition system serves the entire engine (top and bottom plugs). The engine runs smooth on both and on B, but runs rough on A.

Any other suggestions. Also, interested int he carb sync you mentioned.

[Slyfox]

I would think if the synch was off it would do it no matter what you did with the mags. sounds like a spark plug is not working or wire. pull all the plugs on the effected side and check for one to be wet. if you really can't figure what side, remove all spark plugs. inspect.

[Dave S]

AK,

I agree with slyfox to start on the secondary side of the ignition.

No guarantees the Rotax assembly line necessarily got the plug wires on the right plugs...they are human too. Double checking to see if the plug wires are hooked up to the right plugs - due to the wire location...it is possible to have a set of wires swapped between adjacent cylinders....and.... they will be on the same mag if they are. Pretty hard to mix them up between the top and bottom.

If the plug wires are in order I'd next pull the plugs, keeping track of which position they came out of....lay them all put and look for carboned up plugs or plugs that are a different color than the rest...check the gaps too and if there is any crud bridging the electrodes.

If plugs seem OK (they can still screw up).....Swap the bottom ones to the top and V-VS...if the problem moves to the other mag it has to be a bad plug. If not then go to the wires see if there is a high resistance/open circuit or shorted wire somehow.

If it ran badly on both mags I'd then suspect the fuel system....but it doesn't sound like that based on what you identified.

Sincerely,

Dave S

[Ak360]

Thanks all.

Anyone one have a wiring diagram of what should be attached to the A and B portions of the ignition system. Since A seems to be the one with the problem and B runs great, that could help narrow down to the problem and troubleshooting the solution.

For example, does A wire to all the top or bottom plugs or does A wire to some other mix of plugs.

[Slyfox]

just to let you know, if you happen to choke the engine on start up too much, it will foul a spark plug or two.

[kmach]

For example, does A wire to all the top or bottom plugs or does A wire to some other mix of plugs.


Hi,
I have a sheet that I wrote down the info from a search I did a year or so ago.

Circuit A = 1, 2 cylinders TOP plugs / cylinders 3,4 bottom plugs

Circuit B = 1,2 cylinders Bottom plugs / cylinders 3,4 Top plugs

I hope this helps

[Mark]

My engine did this, too. The problem was Rotax had installed one of the trigger coil pickups on the wrong side of the standoffs so it didn't contact the flywheel. Another thing to check. Good luck

[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! :D
(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.