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View Full Version : Engine bog? Sounds like it's bouncing off the rev limiter.



Colo.TJ
August 8th, 2015, 01:50 PM
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?

cheftyler
August 8th, 2015, 03:59 PM
No real two stroke experience but I know when I changed the exhaust on my carb'd 360 with stock sea level jetting it ran a bit leaner than before and the carb "experts" I've talked to said any change to the exhaust will effect how rich/lean the bike runs.

Colo.TJ
August 8th, 2015, 06:17 PM
No real two stroke experience but I know when I changed the exhaust on my carb'd 360 with stock sea level jetting it ran a bit leaner than before and the carb "experts" I've talked to said any change to the exhaust will effect how rich/lean the bike runs.

Symptoms occurred after running the new exhaust 70+ miles with no real issues. I'm NOT saying that the jetting shouldn't be changed for the new exhaust, just that there were no ill effects prior to second ride on new exhaust. At least not to the extent I experienced yesterday.

My "guess" is it's either bad gas, unlikely, or I did something when I power washed it. OR it's just a coincidence. Another member on another dirt bike specific forum stated he had a similar issue with a bad coil. It's NOT really bogging, just not hitting the power band like it should. As I stated, it's like it's bouncing off the rev limiter but much too soon.

cheftyler
August 8th, 2015, 06:33 PM
Symptoms occurred after running the new exhaust 70+ miles with no real issues. I'm NOT saying that the jetting shouldn't be changed for the new exhaust, just that there were no ill effects prior to second ride on new exhaust. At least not to the extent I experienced yesterday.

My "guess" is it's either bad gas, unlikely, or I did something when I power washed it. OR it's just a coincidence. Another member on another dirt bike specific forum stated he had a similar issue with a bad coil. It's NOT really bogging, just not hitting the power band like it should. As I stated, it's like it's bouncing off the rev limiter but much too soon.

Interesting. The fact that you said the other bikes and the genny were having issues as well points to bad gas.

Colo.TJ
August 8th, 2015, 10:42 PM
Interesting. The fact that you said the other bikes and the genny were having issues as well points to bad gas.

It wouldn't be awfully difficult to drain the gas and put in new. I guess I should at least give it a try.

cheftyler
August 8th, 2015, 11:39 PM
It wouldn't be awfully difficult to drain the gas and put in new. I guess I should at least give it a try.

How hard is it to get the tank off those bikes?

R0CKET
August 9th, 2015, 11:25 AM
2. Bad gas.

yep. A stuck fart will hurt a bike as much as it will your gut...

:flipoff2:











but really, probably a carb/jet/air flow issue*

*I don't know what I'm talking about

Colo.TJ
August 10th, 2015, 07:54 PM
https://www.youtube.com/watch?v=HktV2yGtLv8

Colo.TJ
August 10th, 2015, 11:49 PM
Ended up being my EE spark arrestor screen was fully caked. Hence my above video. ;)

I was going through everything including replacing the air filter. When that didn't solve the problem I decided to put the OEM pipe back on just to see. I removed the silencer and noticed how caked it was. I pulled it off and put the Gnarly pipe back w/ the silencer sans the screen and it ran like a raped ape. Front wheel was pulling off the ground. Guess I should be cleaning it more often. :facepalm:

Ordered a pair of replacements to have on hand.

cheftyler
August 11th, 2015, 12:02 AM
:thumbsup:

Colo.TJ
August 12th, 2015, 11:13 AM
The Sun is directly behind the screen in these photos.

http://i263.photobucket.com/albums/ii154/ColoTJ/Cars%20and%20motorcycles%20etc/IMG_2719_zpsjrx9pmrk.jpg

http://i263.photobucket.com/albums/ii154/ColoTJ/Cars%20and%20motorcycles%20etc/IMG_2718_zpsb7pmnsjk.jpg

cheftyler
August 12th, 2015, 06:01 PM
That's a dirty sumbitch rat thur.

PovertyByJeep
October 2nd, 2015, 12:18 PM
Is that silencer packing or carbon?

If it's carbon- I would suggest a rejet and verify your premix ratio (might be a candidate for synthetic premix in the 50:1+ ratios available now), and don't over-oil the air filter.

No matter what- the screens get grungy and eventually clog- but not after one day of riding.

Colo.TJ
October 2nd, 2015, 07:54 PM
Up to that point, I had never changed it. :eek:

BTW, I'm running Amsoil synthetic at 80:1 now. And have about four screens to rotate through the rotation. :D