Rotax Ignition problem. Am I a idiot or just having bad luck?

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Brian Clayton

Well-Known Member
Joined
Dec 7, 2012
Messages
1,042
Location
Ivey, Ga and Centerville,Tn
Sooooo.....

While running my 447 on the ground a month or so ago, it developed a hi speed missfire. So, I went through the usual things like new plugs, check the carb, etc. The problem would come and go. Checked the stator, trigger and coil. Checked okay. Did some crow hops, clean on two...missing on the next two. Doodled around with the ignition again, insulation a bit rotten on the stator, so I pulled it and replaced the wiring. Put it all back together and wouldnt fire at all. The only thing I could figure was a problem in the primary side of the coil (cant check it because of a diode and cap). Hunting around, found a entire ignition and bought it. It came in the other day and to my suprise it "looked" perfect, like it had never even been ran. Installed everything last night, and fired right up. Warmed it it and pulled WOT. After about 15 or 20 seconds....started to miss. So, I started over hunting. Pulled the fuel bowl, looked a little milky. Drained all the fuel in the tank and replaced with new. Checked the float level and pulled the carb apart. Pulled the plugs. None of this mattered, since I fired it back up and went WOT....after about 20 seconds it started miss firing and cut off. No cranking back up this time. Pulled the kill wire loose (nothing else electrical hooked up on engine), no luck....no fire. I have not checked the stator or coil yet with a meter, but..... I am I missing something vital here? Or just having bad luck with used parts?
 

akwrencher

Well-Known Member
Supporting Member
Joined
Oct 16, 2012
Messages
1,407
Location
Gustavus, AK
Any chance you are pulling air through a crankcase seal? Seems like that would show up on the temp gauges, but if the carb jets are clear and there is spark, don't know what else it could be. Do you have a peak reading adapter for a DVM? It's the only thing I've found to test small engine electronics that really tells me much. Not much but I hope this helps.......:ermm:
 

akwrencher

Well-Known Member
Supporting Member
Joined
Oct 16, 2012
Messages
1,407
Location
Gustavus, AK
That's strange, if you changed all the ignition parts. :( I highly recommend getting a peak voltage adapter, if you don't have one. I think mine is a CDI brand. about a hundred bucks. It let's you capture and read things like the trigger pulse, when cranking the engine over. I didn't know what they were for years, caused me no end of grief on outboard ignitions.
 

wizzardworks

Well-Known Member
Joined
Nov 8, 2011
Messages
317
Location
murfreesboro NC USA
Brian, I don't know anything about Rotax ignitions but I was a motorcycle mechanic for 20 years. The British vertical twins all had prince of darkness electrical systems. With those the capacitor would fail pretty much as you describe and shortly would quit all together. They would get up to operating temperature and short out until they cooled down. Same thing on an MG I had. I changed the ignition on the MG and the new capacitor was dead out of the box.
wizzardworks
 
Top