Replaced donuts-still backfires

[apex yooper]

The sled did some more back firing today. First ride since the new donuts.

Now I don't know what to do. If it is a cracked pipe, it sounds like a big problem getting the pipes removed, even to inspect them. It sounds like removing the rivets on the tunnel is the way to do it. Why in hell did Yamaha put that tab on the shield?

Does anybody think that the pieces from the donuts could have gone into the muffler, and causing a hot spot that is igniting the exhaust.

I'm going to try the great idea one of you suggested, about plugging the exhaust with rags, and looking for a leak. Thanks, whoever you are.

Now the most important question. Can the backfiring damage the engine??

I rode in Cadillac today. great conditions.

 

[Randy J Beyer]

Back fire is exploding unburned fuel ! Temp gun needed to measure heat on each cylinder to see
where the cold unburned fuel is coming from?

Back fire will not damage engine under most conditions but have heard where it blew holes in manifolds and exhaust systems.

Pieces of donuts went somewhere ? Maybe time for dealer ?

 

[Attak44]

Mine is doing the same thing. Replaced the doughnuts and still getting a single muffled back fire when decellerating about 30% of the time. I'm checking doughnuts again to see if one is leaking. If thats not it, I'm at a loss as to what is causing the problem.
I have 7000 miles on the sled and have run seafoam through in case an injector might be sticking. No change...could it be valves?

 

[number1kyster]

You have a cracked pipe somewhere.

 

[ReX]

Back fire is exploding unburned fuel ! Temp gun needed to measure heat on each cylinder to see
where the cold unburned fuel is coming from?

Back fire will not damage engine under most conditions but have heard where it blew holes in manifolds and exhaust systems.

Pieces of donuts went somewhere ? Maybe time for dealer ?

In stock form these sleds run so rich when you let go of the throttle that any extra air leaking into the exhaust and you'll get back fires within the exhaust system.

Even with a perfect exhaust, if you do a long WOT lake run (getting the exhaust very hot) and then let go of the throttle you'll hear minor pops and shoot 1 foot or longer flames out of the tailpipes.

I very much suspect there is still an exhaust leak somewhere. This is definitely the most common reason these sleds backfire that I've seen.

 

[Crewchief47]

Randy J Beyer

Please take the time to fill in your location in your profile, site rules.

Thanks!

 

[favarcat]

The sled did some more back firing today. First ride since the new donuts.

Now I don't know what to do. If it is a cracked pipe, it sounds like a big problem getting the pipes removed, even to inspect them. It sounds like removing the rivets on the tunnel is the way to do it. Why in hell did Yamaha put that tab on the shield?

Does anybody think that the pieces from the donuts could have gone into the muffler, and causing a hot spot that is igniting the exhaust.

I'm going to try the great idea one of you suggested, about plugging the exhaust with rags, and looking for a leak. Thanks, whoever you are.

Now the most important question. Can the backfiring damage the engine??

I rode in Cadillac today. great conditions.

I also think you have a cracked pipe. You don't have to drill those rivets out to remove the pipes from the tab. It's easier to remove the flex pipes from the engine so the y-pipes can be slid far enough forward off the tab.
I would ride it for now until the y-pipes are available. Back-ordered now.

 

[vipersj]

Mine has done it since new. Especially after 'hot' rides. I doubt it has a leak. They all seem to have some form or extent of backfiring. Even my riding partners (who have 06's) have some occasional backfiring.
Days (or nights) when it is cold and the pipes are hot, on decel, the unburnt fuel backfires. Apparantly it looks pretty cool....

 

[number1kyster]

I just had my Y pipe replaced because of backfiring. They said my donuts were fine but my Y pipe was cracked.

 

[favarcat]

Never had a backfire on mine in 8,000 miles until the pipe cracked.

 

[aezerskis]

my attack just started back firing, my y pipe was cracked.i drilled out the rivets on the bracket,seemed like the easiest way

 

[ReX]

Mine has done it since new. Especially after 'hot' rides. I doubt it has a leak. They all seem to have some form or extent of backfiring. Even my riding partners (who have 06's) have some occasional backfiring.
Days (or nights) when it is cold and the pipes are hot, on decel, the unburnt fuel backfires. Apparantly it looks pretty cool....

I've never seen a stock, healthy Apex backfire inside the exhaust system. Stock, they pop and light up (shoot flames) just outside the exhaust (when air mixes with the exhaust enough to ignite the right mixture).

If your sled is making loud backfires inside the exhaust (under the seat), you most likely have an exhaust leak somewhere.

Basically after a long hard pull and then releasing the throttle, the exhaust coming out of the engine includes lots of unburnt fuel, but not enough oxygen for it to burn. Once a little extra air mixes with it, if it is hot enough, it will turn into a fireball. If these fireballs are outside the sled, they shoot flames and "look cool". If these fireballs are inside the exhaust, they can make very loud backfire sounds (I find it quite embarrassing to have a sled backfiring loudly inside the exhaust - it makes the sled sound like a dilapidated junker...).

 

[Attak44]

Mine does not make a loud backfire, but rather a single muffled pop. Do you think this is due to an air leak? In the previous 7000 miles, this sled has never backfired.

 

[ReX]

Mine does not make a loud backfire, but rather a single muffled pop. Do you think this is due to an air leak? In the previous 7000 miles, this sled has never backfired.

A muffled pop after a long WOT run is normal. At night you'll see the flames out the back too.

Although at 7000 miles I suspect your exhaust donuts are probably starting to get at least a little crusty...

 

[Attak44]

Its not always after a long run that it backfires. It also does it during normal riding. I just replaced the doughnuts 200 miles ago.