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Hey I have an issue with my 2013 450x bike has low miles . This is gona be long pls be patient , so to sum this up quick I had a head gasket blow so I did a rebuild , new valve stem seals , new piston/ rings gaskets , cam chain . ball honed the cylinder . while the carb was easily accessible I installed a r&d flex screw set it at 2 turns out . bike fired right up went threw the break in procedure . Bike now smokes heavy black smoke when I am hard on the throttle . prior to this rebuild the bike ran excellent . the bike still starts excellent , idles perfect does not pop on decal . I never changed my jetting when I had the carb apart just cleaned it . I have since taken the carb off cleaned it again , checked the float height , checked the fuel screw , replaced the slide o ring seal and the bike replaced the spark plug , checked engine timing , cleaned air filter , checked all hoses into the airbox checked the valve clearances all of which were perfect still smokes black smoke !

I am puzzled ! few days ago I had the coil, stator , and cdi checked with a resistance ,meter all fine there as well . bike has a big gun exhaust , and air box mod, smog block off kit .

current jetting is
165 main
42 pilot
ncvs needle 4 position
r&d flex fuel screw 2-1/4 turns out

Welcome to the site !!

First , what is your elevation ?? , its pertinent to jetting correctly

Have you confirmed this is fuel smoke ?? , does it smell overly rich from behind ?? , like does it burn your eyes ??

How are you confirming its black smoke when under hard power ?? , are you looking back and seeing a trail of smoke behind you ?? , or is someone else confirming this ?? ,(i am assuming this is taking place while under a load and riding) if anything if it was overly rich , it would most likely blubber at lower RPM's or idling , not upper RPM ranges , you may also want to post this in the Jetting portion of the site , we have a resident jetting guru (leardriver) , and IF it is a jetting issue , he would be the one who can confirm or trace your issue

I am thinking this may be a ring gap placement issue as opposed to a rich issue , (not saying this is what it is , but i would lean that way rather than it being too rich on top end)

The choke is off I guess otherwise it would run poorly at low revs.
The airclean is clean and not over oiled?

Take it for a run and when spewing black smoke cut the motor and pull the plug. Black and sooty look at fueling. Black and oily, look at rings and piston clearance.
The fact you have used a ball hone is worrying in itself as they tend to tear the coating on the bore. You normally clean up the bore with solvent and scotchbrite as you are actually cleaning carbon out of the original hone marks.

Hey guys tks for the replys , when i pull the plug its very sooty , bike has gone down some engine oil but nothing out of the ordinary . My buddy riding behind me has seen the black smoke fr time to time bike seems to run ok no hesitation just a little under powered compared to my buddys 450x , my white rear fender is also very black an dis-colored fr the soot coming fr the exhaust . i notice it mostly if the bike is stopped and i give it a quick shot of fuel it puffs out a black cloud .

forgot to mention i live on the east coast of canada right next to the atlantic ocean , so i am at sea level . Temps can vary here significantly before my rebuilt there was no issue with jetting though .

How much break-in time on the bike? As in, was this phenomenon immediately present before you rode the bike a half hour or so?
Your jetting is fine. If anything, your pilot should be a 45, but that is more of a starting and idling setting.

How is the bike's power? Maximum mojo or down on power?