A few weeks ago I did some engine mods to the Raptor.
High comp piston, Stage 2 cam, Titanium valve springs, K&N high flow filter kit, Removed lid to air box, Alba jet kit,new needles raised all the way, 27.5 primary jets, 155 & 165 main jets, Alba pipe.
We ran the bike on the dyno and it went from 31 to 45 HP.
Motor was running pretty good, It seemed to be a bit rich on top but I Had no problems the whole weekend at Silver lake, No problems at Fox Valley, But then I went to the Badlands and after about 3 hrs of riding the bike suddenly started running like crap.
Got home, did some routine maintainence. New plug, clean air filter, change oil,ect,ect. When I was all done with the routine stuff I started the bike and it still ran like crap. So I figure while Im at it I'll rejet the right carb and lean it out 1 size.
As Im putting the carbs back in I noticed that the vent tube was missing off 1 of the carbs. I stole a vent tube off the wifes bike and stuck it on and now it seems to be running just fine again.
I noticed that the vent tube has a 1 way check valve on it to allow gas to flow out if needed without sucking air and dirt back into the carbs.
Does that vent tube really make that much differance?

 

What kind of jets are you using, mikuni or dynojet?

 

Using Mikuni jets.
I dont think jetting is a problem. Bike ran fine for weeks.
Dyno readings say jetting was pretty close, just a tad rich on top end.
Then all of a sudden, out of the blue, it starts running like crap.

 

I would think your are scary lean with those mains but I don't know what kind of needles are in the Alba kit. I put together a 686 11:1 stage 1 and the plug looked perfect with 180/185 mains and went up to 185/190 to make sure it was a little rich. Running lean with your mods will more than likely result in rod failure.

 

Those vent toobs are important...they make a significant difference in the rough

It does sound like you have to small of jetting on the main...did the dyno have a true gas analyzer?

 

I replaced the missing carb vent and ran the motor.
Once it warmed up it started running like crap again.
Yes the dyno has a true emission analyzer. The plug is a nice tan color.
Found the problem. Intake Valves went out of adjustment. Dont know why but they tightend up.
I readjusted valves and after running it for over an hour it still runs great!!!!