2017 YZ250F blackish smoke on cold start rev

[TomTopDog12]

Hey guys 

 

 

picked up a 17 yz250f not long ago with 42 hours on it. A OEM piston kit was installed 2 hours ago, the bike being broken in well i'm getting kind of worried at the sight of smoke out the exhaust on cold start warm up.

Here's what will happen;  I will cold start the bike and everything running fine, after i turn the choke off i'll let it warm up good for 3 to 5 minutes or until the cylinder/rad are warm. Upon giving the bike a small blip of the throttle it will emit a blackish smoke that is sort of thick but only for a second. After the bike is warmed up and hot it does not smoke what so ever. Power is fine and it starts first or second kick out on the track/trail. Is this normal for YZs? I'm a KTM guy so i have no idea about the tendentious these motors have.  Could this just be a bit of oil leaking from the valves that aren't fully warmed up? 

 

Any advice would be fantastic. 

[RamblingRMZ]

How long was it sitting and is gas good 

[ChampWazza]

Sounds like rich fuel settings...check your ECU maps. But, if if performing the way you want, starting, riding/racing....then leave it as is mate.

[DarrellH3]

The fuel infected Yamaha's run rich while warming up. Nothing to worry about. It's just gas smoke.

[Max17]

We pretty much never use the choke on my son's '16 YZ250F -- even on cold days and we aren't very far away from you -- and it always starts fine.  Have you tried starting it without the choke?  Maybe it's just getting too much fuel initially.

[Scralatchtica824]

My 18 WR250F does that on cold starts. It runs extra rich idling until it’s warm and has a lot of carbon/raw fuel in the exhaust. As soon as I blip the throttle it emits one good airy black puff and she’s ready to rip.