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