Seat Fire...Listen up!!

[JDKRXW]

So do you know if the muffler or pipes let exhaust escape under the seat?

 

[smokeless1]

So do you know if the muffler or pipes let exhaust escape under the seat?

Nope.

But the sled had none of these issues before and it only has about 300 miles on it. Numerous trips, tho short, and no troubles.

Not the case now, and it happened so very quickly.

I think back at the gas station and there was nothing to support any trouble then either, or we would have never started out. Sled ran fine.

Whatever it was just happened, and I am at a loss to explain how this could get so hot so quickly.

 

[SuperStroker!]

I find it hard to believe some think this problem is from gas in the muffler. Think about this for a minute. You have fire coming out out of the engine on one end and fresh air on the other. The muffler is so hot you can light a cigarette by touching it. Now your gonna tell me there is fuel in it. He would have seen flames shooting out the back not sparks of burnt soot embers. More than likely the muffler would have been blown wide open when the fuel ignited had there been some.

Here we go with the words confusion game again!

When we say fuel in the exhaust, it means in the form of burning fuel w/air, (it would have to have air or it wouldnt burn) yes>>>>thats obvious!

If one or more cylinders are not firing, because a plug fouled, the burnable GASES will ignite outside of the combustion chamber like a flame thrower and heat the exhaust.

If the ignition timing (retarded) is too late, in essence, if you screw up the timing while making a change, the exhaust valve will open while the charge is still burning and throw pressurized flame (from late combustion) out into the exhaust and do the same thing.

The sparks were obviously coming from a source (parts around the pipe) that had melted onto the pipe and had begun charring.

All of this seems like it could happen but to me its still highly unlikely????

But I guess It did???

 

[RobX-1]

For the guy who thinks you should stop everytime your engine coughs, or sputters, you have to be kidding?? Moisture, soot, hickup man the list is endless, and if you stopped to see what was going on, you would take hours to go a mile.

...and by all means get the he!! off the machine if it starts to misfire for any reason whatsoever.

So, which one is it?

 

[smokeless1]

For the guy who thinks you should stop everytime your engine coughs, or sputters, you have to be kidding?? Moisture, soot, hickup man the list is endless, and if you stopped to see what was going on, you would take hours to go a mile.

...and by all means get the he!! off the machine if it starts to misfire for any reason whatsoever.

So, which one is it?

Hey we have all had a hesitation, or sputter, which usually is nothing. What is evident here is there was almost no notice of trouble. Bit of hesitation, (gee was that a hesitation, or was it just a slight slip on the throttle, etc) There was a couple misses, but consistant with a bit of water in the system which could easily have happened with the steady snow fall. I did not ride the machine, but my friend is no dummy. It wasn't trying to die, or was there a steady miss fire. Just hesitation and a few pops which were apparently telltales that should have brought him to a stop. We were close (few hundred yards from camp) and he had no idea that what happened tho only slightly telltale, would result in a seat fire. Hindsight is always twenty-twenty.

But you need to know THIS COULD HAPPEN TO YOU, OR YOUR SLED. SAME SLED, WITH SAME CAPABILITIES. You decide if you need to stop or not. But at least you know something my ridding buddy didn't know and that is if there is even ever so slightly a motor issue, hesitation, popping or sparkplug miss....GET OFF THE SLED. And check it out.

 

[RobX-1]

I agree that after reading this post, one should probably check things out. My point was that someone else suggested the same thing you ended up suggesting at the end of your post but you harped on him for suggesting it.

And you are correct...I now know something that your riding buddy did not know at the time and will always keep that in mind.

 

[ReX]

smokeless1,

Do you have any pictures you can post?

 

[LazyBastard]

I have a few questions about that sled...

1) What (if any) modifications have been done to it?
2) What (if any) parts have been removed or reinstalled?

 

[Sled Dog]

I find it hard to believe some think this problem is from gas in the muffler. Think about this for a minute. You have fire coming out out of the engine on one end and fresh air on the other. The muffler is so hot you can light a cigarette by touching it. Now your gonna tell me there is fuel in it. He would have seen flames shooting out the back not sparks of burnt soot embers. More than likely the muffler would have been blown wide open when the fuel ignited had there been some.

Here we go with the words confusion game again!

When we say fuel in the exhaust, it means in the form of burning fuel w/air, (it would have to have air or it wouldnt burn) yes>>>>thats obvious!

If one or more cylinders are not firing, because a plug fouled, the burnable GASES will ignite outside of the combustion chamber like a flame thrower and heat the exhaust.

If the ignition timing (retarded) is too late, in essence, if you screw up the timing while making a change, the exhaust valve will open while the charge is still burning and throw pressurized flame (from late combustion) out into the exhaust and do the same thing.

The sparks were obviously coming from a source (parts around the pipe) that had melted onto the pipe and had begun charring.

All of this seems like it could happen but to me its still highly unlikely????

But I guess It did???

My point is I beleive the heat was not caused by gas entering the exhaust system at all but by a restricted exhaust which caused the exhaust temp to rise along with the exhaust pressure. The flame thrower theory I think a none restricted exhaust would allow enough gases to go through it carry the heat along with its so that most or all of the heat is gone to the atmosphere. I can see it getting hotter than normal but not cherry red hot. Read my former posts.

 

[SumpBuster]

Just like my bolt/bracket rubbing reply, we need to pay attention at all times to what is happening while riding..as with any motor vehicle burning a fuel. Bad things can happen to anything. Now, I had a 93 MXZ which used to get frozen carbs. During the blizzard of 93 in March, I had my hood vents duct taped shut to keep out the loose blowing snow. My exhaust glowed red, sparks came out, and started melting the belly pan and donut. You know what burnt in there? Think chimney fire. All the carbon caked up in there became fuel when the temp was right. Just like in a dirty chimney.
If the sled was running perfect, nothing unusual at all, maybe this is a possibility?? My RX exhausts get pretty black on the inside...

 

[polecat]

hot exhaust

I had the same problem with a 03 but I had the seat off. The problem was the throttle sensor was not working causing the machine to back fire like a rifle and the entire exhaust was red hot. l by passed the throttle sensor and the engine ran fine. I then installed new spark plugs and connected the throttle sensor and the sled runs fine. Seems the throttle safety switch causes the engine to misfire like it is retarding the spark or telling the computer to shut down the engine. If you get any type of backfiring, shut down right away and disconnect the throttle switch, which takes all of 2 minutes and the problem should be over. Make sure you find the problem with the throttle switch though. I had Arctic cats, T cats & 800 zrts and would disconnect the throttle switches and by pass them, as they were a problem for Arctic

 

[SumpBuster]

But you did have a noticeable problem that needed attention. Lean exhaust is hot...check out top fuel pics!!! Maybe an exaggeration, but I've seen farm tractors with straight pipes blow blue flames right out!! HOT.

 

[Tfin]

The fuel accumulating in the pipe makes sense. As does the apparrent fact that the sled seemed to be running fine at 20 mph or so (with the several pops, or skips in the engine).

Here's an example:

I had an XLT at one point in time. I had cleaned all three carbs, but didn't hook up one of the throttle cables properly. Only two were opening when the throttle lever was squeezed. The sled would start and run fine.....up to a certain speed.

Point being, a fouled plug (or closed carb slide) would in fact dump exessive fuel into a cylinder, and ultimately into the exhaust pipe......and at only 20 mph or so......one might not notice a difference in performance in the sled's operation....other than a slight pop or misfire.

So the accumulation of fuel in the exhaust and the fact that the sled appeared to run smooth (other than the said pop and/or skip) theoretically could happen simutaniously under these conditions.

 

[kviper]

RobX-1 thank's for pointing that out. This was definately not a good thing reguardles of what caused it and i am glad no one was hurt. Almost all these theory's are possible. But just remember, There are thousand's and thousand's of these sled's out there and this is the first one that i have herd of with this problem and maybe two if the other one is fact also. As some one said earlier any thing that operates with an egnitable fuel has the potential for fire. Pick any model car on the road to date and i will bet one has burned some where. My point is these sled's are not time bomb's and no one need's to be afraid to ride them. Also IMOP Yamaha is the best in the sled biz as far as taking care of there customer's so if they don't stand behind this problem then it was just one of those sh1!! deal's that just happen's. It will be real interesting to know the out come. kviper

 

[Snowman269]

If you have one dead sparkplug, you will be pumping a perfect mix of air and fuel into the pipe continuously (source of oxygen AND gas), which wouldn't be ignited UNTIL it gets INTO the pipe. You could get yourself a continuous flame that is confined to the pipe. If its popping and sputtering and generally running badly, thats a sign that a plug may be dead, the popping would be the fuel igniting in the pipe.

LB, You are right on the money!

On a different note, the YZ250F & YZ450F header pipe will glow cherry red from excess fuel ending up in pipe. Once in the pipe it gets enough O2 to burn.

FI, where are you?