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thredbo

Smoking exhaust for 10 mins after engine turned off

21 posts in this topic

Took my yz250x out for a rip earlier this arvo, and when I came back and shut it off the exhaust kept smoking (about as much as a candle when you blow it out) for around 5 - 10 minutes.

What could cause this? Only thing I can think of is maybe I set the exhaust packing or some carbon build up on fire somehow, so I plugged the exhaust to starve it of oxygen and it seemed to die within a few minutes.

Any ideas?

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Smoke from the exhaust for 10 minutes is a good indication that you downshift motor is getting way too hot.

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Could be it I guess. The radiator cap didn't feel hot at all though, was cool enough to keep my hand there.

Am I gonna damage my engine by going that hard on it? I thought 2 bangers were built to be screamed...

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Has anything changed recently… Jetting etc.? Was The "rip" you last went on faster (higher RPM) than usual? Smoke like that usually means there is carbon or oil built up in the pipe/silencer that reached a temperature not usually seen before or at least at the end of the ride where it can be noticed. I wouldn't be too alarmed, maybe time to clean the pipe and repack the silencer.

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Yeah, I started riding at sea level (normally ride at around 600m) and I was definitely going faster than usual. Probably need to rejet a little

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Maybe lean at some throttle position.

Take the pipe off. Inspect the front of the piston skirt to check for abnormal wear.

Take the muffler off and pull the core apart. See how much oil is in there. Maybe you just burned it off.

It's normal to smell that burned fiberglass smell if you hammer a 2-stroke for a while with a freshly packed muffler, or if the jetting is a bit lean.

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sounds like the pipe is full of oil.... what pre mix do you use? might be a touch to much oil?  @arthur6 whats this down shift motor??? 2nd time iv ever herd of it and both times from you please explain id like an education on this mysterious item.

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13 minutes ago, thredbo said:

Yeah, I started riding at sea level (normally ride at around 600m) and I was definitely going faster than usual. Probably need to rejet a little

What it is, is that you are more than likely jetted for the higher level, and I'm guess it was slower, more technical riding.

Then, once at sea level and going faster, the bike leaned out a bit and was generating more heat in the pipe. That allowed you to get more heat in the pipe an all the oil that built up in the pipe from the higher level riding started to burn out.

You more than likely stopped the bike after a hard on the gas run and the oil was still smoldering in the pipe when you stopped.

Actually, it's a good thing, but you may want to make sure your jetting is good for the riding you are doing now.

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3 hours ago, 218 said:

 

You more than likely stopped the bike after a hard on the gas run and the oil was still smoldering in the pipe when you stopped.

 

^^^ what he said.

I've had this happen before.  06 YZ250

I ride alot of really tight nasty woods, several hours per week.  I mean really rocky, rooty, hilly NEPA single track.  Mostly 2nd gear part throttle stuff, I'm a Senior A guy.

Then I'll ride moto, and I'm certainly not the fastest.  But give me an hour or so, and I'll dial in all the jumps on a particular track.  

When I make the switch from woods to moto, I've had this happen before.   You know the black drool that comes out your silencer, whelp its "burning" inside the front part of your pipe. 

That's the source of your smoke.  

 

Edited by R and D Marine
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I've had this happen to every 2 stroke bike I've owned.

1/2 my rides are slow low rpm lugging stuff and 1/2 of them are faster on the pipe stuff, I always jet a hair rich to save the motor while riding the fast stuff so it spooges a bit riding slowly.

The next fast ride after a lot of lugging the spooge burns out of the pipe making the bike smoke a bit after shutting it off.

Repacking the muffler often will cure this but I just let it smoke once and a while.

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There is a place where we ride that includes a lot of slow riding on very tight trails, but we have a lttle "grass track" set up in an area that allows lots of full throttle and very high speeds.  When we take a break after the track ride, most everybody's bike continues to smoke after shut off.  The heat from the high speed riding is presumably burning off the spooge from the slow speed riding.  I don't think you have anything to worry about if the bike is running well.

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repack your silencer.  It is soaked with oil from your normal riding and you must have been riding it hard the last ride and heated everything up enough that the soaked packing is burning a bit.

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I had this happen. 35 miles of mountain single track to an 80 mph rip up the highway to the bar. :excuseme:

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On 10/18/2017 at 7:52 AM, arthur6 said:

Smoke from the exhaust for 10 minutes is a good indication that you downshift motor is getting way too hot.

what is a downshift motor ?

 

smoke from a hot two stroke is totally normal. there's a lot of carbon/oil in the expansion chamber and silencer, and sometimes it smolders. 

 

totally normal

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I asked the same question   what is a down shift motor?? never heard of them ether.

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1 hour ago, arthur6 said:

Other than the downshift motor overheating, you could run less oil mix in the gas. We run close to 100:1.

 

uhhhh, no, that makes no sense. you don't change oil ratios for altitude conditions, you change jetting....

 

and it's getting a lot of high speed riding, you certainly don't change to a lower oil ratio. 

 

these are two totally different ratios, oil mix vs fuel/air mix. 

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Had it happen few times when ive rode a slower riders bike . Burns off the excess oil in packing.  If you ride around putt putt for while then get on the gas will burn oil out. Keep riding like that it will clean out some

Edited by Motox367

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6 hours ago, 2strokeYardSale said:

First google image result of downshift motor....

 

Downshift-1-Lowrider-1.jpg

That's funny.
Pics of two different downshift motors...(real motors)

IMG_20160704_184342_zpsdzqtrzxc[1].jpg

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