Engine bog? Sounds like it's bouncing off the rev limiter.

Bike- 2014 KTM EXC-W 200. 28.6 hours. 419 miles. 1 year in service. Was jetted by dealer at purchase. Recent mod- FMF Gnarly pipe. No rejetting. Not sure if needed?

Issue- When it begins to get into the power band/pipe it starts to what I can only describe as bouncing off a rev limiter. Sometimes it will get a bit deeper but than starts. Worse in higher gears. Makes what feels like normal power at lower RPMs and lugging until you actual need more power like climbing a hill, then you can feel it struggling. Rode it once after installing the Gnarly pipe without issue, it seemed, for 71 miles of high speed fire roads and 48" trail and single track. Maybe a difference in the torque curve with the Gnarly pipe hitting later and without quite the same hit as the stock pipe. In other words, a bit more tame/controllable. Thought that was part of the design by FMF for the Gnarly pipe.

Possible issues that I can account for.

1. I washed it after my last ride, as usual, with a power sprayer. I'm always cautious but human.

2. Bad gas. Not sure if I've ever gotten bad gas before but all the other bikes and the generator seemed a bit "off". Everything ran but didn't seem as "smooth". Maybe it's wishful thinking but thought it worth mentioning.

I changed the spark plug in hopes it was just fouled. The installed plug was the first replacement of the OEM and didn't look too bad.

3. Needs jetting. As mentioned above, it ran quite well after installing the Gnarly pipe and no re jet.

What say the 2 stroke experts?

 

https://www.youtube.com/watch?v=HktV2yGtLv8

 

Turned out to be a very coated EE spark arrestor screen, hence the above video.

The Sun is directly behind the screen in these photos.