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Discussion Starter #1
I put a mbrp trail silencer on my sled about a month ago, which is a 01 700 mxz for those that dont know, but anyhow since then when i pull the cord to start it alot of the time it will backfire rather than start.  I check my plugs at least once on every ride at some point to see how its burning and its always a nice tan color, and when i first put on the silencer i checked my plugs about 20 times at different speeds to check the burn and its was still a tan color burn, so i dont think its caused from a lean condition , nor a rich condition, or is it because of less back pressure with the straight flowing can?? so all i got to say is WTF?? What do you guys think??    Geeez that was my longest post yet!!!
 

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I was going to ask the same thing about the high idle. do you let the sled idle down before you shut it down?? My Summit800 used to do that to me all the time and the dealer told me that the flat slide carbs last year were not wery good and suck too much fuel at the last second of shut down.
 

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I have the race can (or at least a can that looks like it but isn't) and my sled started backfiring on shut down...flames shooting out about 3 seconds after i kill it. But that was only on really warm days...like above 0C when I am jetted stock, so I know she's running real rich. It is not the can Justin...
 

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Discussion Starter #5
Mine does it even when its cold and frosty out, some times i will get a little !poof!  when i shut it down but its after really hard riding for some reason, But i get a big bang alot when i start it, just tonight i pulled the cord while on the trail and my buddy thought i was going to the moon because i lit the trail up with the flame shooting out the pipe.
 

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I would say you must be really rich in your idling then...do you let the engine calm down before you kill it?
 

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Discussion Starter #7
Yes i think i am a bit rich at idle because i foul plugs somtimes at idle, and i no i dont always let it idle down before i kill it.  But heres somthing else for ya, my buddy who i ride with has a 97 670 and if he dosent let it idle down before he kills it he will have to pull it 3 or 4 times to get going again, but if he lets it idle down it will always go first pull when we go again.
 

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my 670 will usually start 1st pull when warm..only if I give it a bit of throttle...if I miss it on the first pull...then I have to pull all day to get it going...still can't figure out why
 

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Discussion Starter #9
yes my buddy has to hold the throttle a bit as well to get his to catch, all carbs are funny in there own way, but are all a pain in the butt at times.
 

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rocketman,
 every now and then my sled does the same thing, then i go to full throttle pulling so fast that i don't let the engine quit spinning before i give it another pull again and again till it goes.
 

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Discussion Starter #11
Paul what do you ride?? a 670 too?
 

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jwheeler,your post up there is almost as long as some of Machzzzz1s


If you have flamage out the pipe,you are rich.All that unburn't fuel has to ignite somewhere.
 

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Discussion Starter #13
I must be rich at at really low rpm then because im running perfect around the mid and top range. i will have to kill it at really low rpm and pull the plugs and see.
 

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How new are the plugs? Did the problem start when you put new ones in? I had a similar problem this year on my 98 Mach Z (I ran a B&B can for two 1 1/2 seasons with no problems but switched to a DNE this year - I also suspected my can so I put the stock unit back in and the result was the same).

First thing in the morning the sled usually starts on the fourth pull. This year however I put a new set of BR10ES plugs in it and since that it would backfire on the fourth pull and then start on the fifth. I put on less than 100 miles this year and then my CDI box went. I figured the backfiring was a result of the box being on its way out but it continued to do this with the new cdi. I decided to try a set of BR9ES plugs as Doo recommends switching to a hotter plug if you experience fouling and this solved the problem. The thing I don't understand is that I ran the 10's with no problems before. I figure maybe I just got a bad set of plugs (a few years back I fouled all three plugs at once on my 95 XCR 600 and they had less than 50 miles on them - it ran fine on my way over to a buddy'd but wouldn't start again when I shut it off).
 

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Discussion Starter #15
no its been doing this with now the second set and soon to be the third set, i dont think i want to try a hotter plug and burn it up though.
 

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Discussion Starter #17
I was thinking that the loss of backpressure with the mbrp can might do it. I am going to do some more tinkering tomorrow and probably try the stock can and see if it will still backfire.  I will let you guys know.
 

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IF, you are idling high and it wont come down by adjusting the idle screws your pilot air screws are too lean, screw each one in evenly until the idle drops.
Could also have damaged reeds, pull them and check for cracked or bent peddles. Some of the twin doo's have a problem with the rubber the peddles seat on coming off! Back firing is the number one cause of peddle failure
 

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I'd check the idle, See I bought that exact same can for my 00 mxz 700. Before I even rode it this year I put the can on and turned the idle up on my sled and it started backfiring. This is not a good thing for your motor at all. It may be coinicidence but I just had my whole motor rebuilt, Top to bottom. I put the can back on when I got it back, My sled didn't backfire once the last trip I was on and I rode about 550 miles. Something may be going on your sled, How many miles? It could be the center seal on the crank or a number of things.
 

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Discussion Starter #20
Its a new engine i got this winter with only about 1100 kms on it now.
 
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