426 header pipe smoking

I am just finishing putting my bike back together after I had it ALL apart. While I was having the frame powder coated I put in a YZ450 auto decomp cam. I also changed the jetting back to stock since I was putting the stock pipe back on it.

The bike has fresh oil and coolant and started up easily after a few kicks (I am sure it just needed some primary since there was no gas in the carb). I like the auto decomp cam-I started the bike wearing cheap flip flops and there was no starting routine.

My question is after only about 10 seconds of idling with the choke on the header started to smoke. I shut off the bike and wiped down the header-thinking maybe I had gotten oil or coolant on it. I started the bike up again, shut off the choke, and kept it idling with the throttle. Again after only a short time the header really started to smoke. The cylinder doesn't feel hot to the touch but the pipe certainly does. Is this a jetting issue with the cam or did I screw something up when I installed the cam?

The pipe normally runs very hot (to the point of glowing in the dark, even), but if you feel uncertain, maybe double-checking the cam timing would be a bad idea.

Did you use an OEM 450 cam, or aftermarket? How did you time it?

These bikes were not made to sit and idle. You will notice at night that the headpipe will actually start to glow red if left idling for any decent amount of time.

As for the smoke, you could have spilled some oil, wiping won't always take it off. Check for leaks where the headpipe comes out of the cylinder. You may also want to take it for a quick spin and see if the smoking stops. I guess it all depends on where it is really coming from, but my guess is some residue that will burn off in a few minutes.

^^haha, gray beat me to it while I was typing. :ride:

You may have got something on it that you sprayed...I sometimes get WD-40 or something on my pipe, and I can't see it or notice it, then it will just burn off. Try riding it for a little bit. Was their any water or moisture in the pipe?

The pipe normally runs very hot (to the point of glowing in the dark, even), but if you feel uncertain, maybe double-checking the cam timing would be a bad idea.

Did you use an OEM 450 cam, or aftermarket? How did you time it?

It is the oem 450 cam. I had zip tied the intact cam so it could not move from the chain. I then set it so that the valve ends (looking at the cams from the right side, as if you were riding the bike) are symmetrical.

I do know these things can glow red, my wifes YFZ450 does when she putts around at night. My exhaust header had not smoked before, let alone after only 10 seconds. I will try to cruise it up on down the street this weekend and see what it does. I am thinking I got something on the pipe but wanted to check with you guys before I assumed it was nothing and killed the motor. If I didn't get the timing correct will that cause damage if I ride it a few times?

it is fine all of the head pipes smoke for about 5 min when the engine has been taken apart. why? only 1 reason u touched it w/ dirty hands.

hey i just started mine up yesterday for teh first time. the header started smoking bad after about 5 secs of running. i shut it off and looked and then just started it up again and the smoke went away.

by any chance when u had ur motor apart..did u polish the head pipe. we polished my botheres on his 400Ex quad, and it smokes a bit when he first went riding...now its all cold and blue again...dangit!

hey i just started mine up yesterday for teh first time. the header started smoking bad after about 5 secs of running. i shut it off and looked and then just started it up again and the smoke went away.

Ya but I made sure I put oil in my bike before I started it...

I'll bet you were sober, too.

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