Rotax Evo 125 DD2 Misfire @ 8000 RPM

Hi all,

I need some guidance with my DD2… it has a strange misfire… feels like it only happens above 8000 RPM, but only before the power valve opens… once the power valve opens, it doesnt misfire anymore…

I have checked the wiring, and I dont see any obvious damage to any of the wires. I have also cleaned and sprayed all the connections with electrical spray.

I thought it might be related to the shift cut, but that isnt shorting anywhere either.

I have cleaned the carb, and taken out and wire brushed the spark plug.

I checked the battery terminal connections, all good. No other loose or damaged wires in that area…

I dont see any fuel leak between pump and carb, and rest of fuel system.

Any ideas?

Thanks in advance!

Edit: This started at our last club event. Since then I havent been back to the track, but I get the same misfire on the stand, in neutral and first and second gear…

The joys of DD2. From my experience (I was in and out of the Rotax tent after almost every practice session at the 2021 Grand Finals with similar issues - it wasn’t until they finally replaced the wiring harness before the last practice session that the problem went away) - it is most likely either:

(a) wiring harness - you’ll never know unless you replace it, which is expensive and a bit of a pain
(b) fuel pump - easy to replace the insides of the fuel pump and the newer DD2’s have had all sorts of fuel pump problems - this is the first thing I’d try
(c) starter switch - they tend to have issues, especially on the DD2’s… it’s a cheap and easy replacement part and good to have a spare on hand

If you’ve looked at the carb, the plug and the shift cut system, other things you can look at that I’ve occasionally seen cause problems include crank sensor, ECU, spark plug boot or a sticking power valve.

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