smoke on start up

[Dr89]

so just wondering if i have a problem? my yfz has very few hours on a brand new rebuild....everything was taken care of, piston, rings, cylinder, crank and rods, gaskets, the whole bit. anyways if its been sitting for a while, as in over night or days at a time, and i go to start it up it will back fire some and throw out puffs of white smoke. this only happens when the engine is really cold and needs to crank a few times to start, when its warmed up i just hit the button and it starts up instantly no smoke etc...when it does smoke a little however it only lasts for a few seconds, maybe 30.

im not losing any coolant or oil what so ever that i can tell, even after hours of riding. so i was wondering if it could just be some left over oil etc. that they might have used while rebuilding it? i also just repacked the pipe but i dont think its coming from there. the guy who do the work is extremely knowledgable and incredibly experienced so im hoping this is just common with break in??? it runs like a champ btw!

[f4istunna]

a few puffs on start up is fairly normal from my experience, Valve seals will do this too.

Is it doing it while choke is on?

[Dr89]

yea...choke on choke off it doesnt make a real difference i dont think. seems like it might be the valve seals from what i've read but...i just dont know why they would be doing that. i prolly wont worry about it since im not losing any of the fluids and it runs fine, fan kicks on and stuff so...i dunno.

[CSR400EX]

my 450r does it too. its kinda black but its got a bit of blue in it as well. it goes away after its warmed up

[Dr89]

yea doesnt seem like to much of a problem, anyone else?

[atvmaster0927]

yeah, my 400ex does the same upon start up...its perfectly normal. It does it because it is cold and sometimes because the oil stays on the exhaust whitch burns and makes white smoke.
Hope this helps.

[nick249420]

are you still in the break in process .. if so it will smoke untill fully broke in
it could also be condensation
i wouldnt worry about it unless it gets worse

[d3ktrix]

My guess is condensation if its white smoke.

The backfire I dunno, prolly pilot jet/AF screw.

[Dr89]

its not condensation...its to "heavy" as in it doesn't disperse quickly, it kinda rolls out. but i dont think im gonna worry about it

the jetting is on, i think the backfireing may have been caused by some exhaust leaks, i tried to fix that with some high temp silicon gasket filler, it'll cure over night and i'll check tomorrow if it helped anything.

anyone know if some minor exhaust leaks like between the header and the silencer, and where the silencer pipe part meets the chamber could account for some backfiring?

[d3ktrix]

Doubt an exhaust leak at the header/silencer junction would cause back firing during start up, its too far back. A leak at the header/head connection could cause all kinds of problems though.

My sparks pipe had all kinds of leaks at the front of the silencer and at the mid pipe joint. I thought it was causing my popping on decel, so I RTV sealed it. Turned out to be jetting though.

[Dr89]

well after running it around some today i actually think the silicon helped quite a bit with the hard popping on decel, still does a little bit so i may have some gaps on the backsides that i couldnt see, or maybe the jetting is a little lean.

after reading up on some of this stuff about "hard break ins" (which was news to me...guess i've had to many 2 strokes)...anyways i decided to try it out, i took it up and down the road a couple times...WOT!! and so far thats actually cured the smoking problem??? but it hasnt sat very long yet either so...we'll see.