[valleyml]

Hey there. I'll try and explain this as quick as possible and hopefully I can get some responses from some of you. This is my second year with my XC 600 and this year I put on a rumble pack cannister and did some clutch work and a new 1 1/4" track, it ran good for about the first 2oo miles and then started backfiring in the midrange. It gradually got worse and does it all of the time in the midrange. It idles great and wide open it runs great. I've checked the carbs ( clean ) reeds ( no cracks ) plugs are fine ( changed to a hotter plug ), changed plug caps, and have played with the air screws on the carbs ( right now I have them a 1/4 of a turn out and seems to have helped a bit but not much ) Also it is not the CDI. Any ideas or info would be great. Polaris is my way out!!

 

[hotrod]

Is it backfiring during cruising, accelerating or decelerating through the midrange?

 

[valleyml]

Hey thanks for the reply sorry about the wait on my behalf. It is backfiring during cruising and accelerating. On accelerating if you pin it it will back fire once and then it will be fine and on cruising , when you hold the throttle steady it constantly backfires. This may help you a bit....when it was in the shop at a buddies of mine, it would not back fire when it was on a stand, when the track was free. He would rev it up and it wouldn't backfire at all. Maybe because it had no load on it? Could it have anything to do with the ignition?
Thanks for the response once again!

 

[hotrod]

Heres two things I know off that cause this type of back fire. One, too rich. Are your plugs dark and wet looking. two, bad plug or wire. Have you replaced the plugs at all.

 

[valleyml]

I've put 3 sets of new plugs in and one of the plugs is nice and brown and the other is fairly brown but a little darker, but not much difference. I've also replaced the spark plug caps.

 

[hotrod]

Hmmm... I will think some more

 

[valleyml]

Thanks please do! It's been a mystery for us!!

 

[valleyml]

Thanks again hotrod for the help, anyone else out there have any ideas at all? Or has someone had a problem like this before?

 

[hotrod]

I worked on a friends cat once that had a similar problem and it turned out to be his tether cord connection intermitantly losing contact. Is it possible during removal of the air box for maint. that one of the electrical plugs came loose. Another time same guy different cat we found an obstruction in the exhaust muffler causing the back-fire. Im still thinking.

 

[zackattack]

First of all. The air screw controls idle to 1/4 throttle. Your screws should be about 1 1/4 turns out. Your needle jet in your slide controls the midrange of throttle. Run your sled in the bad range as much as you can stand then imediatly shut it off. Check the plugs and look at what color they are and if they are consistant. This is a good place to start.

 

[hotrod]

What ZA said is good advise. it works better if the sled is under load, like a 1 minute blast at half throttle through some deep snow.

 

[valleyml]

Thanks for the help and info, I'll try it in the midrange for awhile and try what you said, if they are consistant then..... go from there I guess!

 

[valleyml]

Hey hot rod would something in the exhaust make it backfire that bad and if so how large would the object have to be? What was in that cat you were talking about?

 

[valleyml]

By the way I'll be sure to let you guys know when I or we finally figure this thing out!!
Thanks again for the replies!

 

[hotrod]

It was a 700zr and the resonator had colapsed inside.

 

[valleyml]

Oh, o.k thanks.

 

[gbaronet]

Could it be a lean pop..? Partically plugged pilot circuit.?
Have seen this on a car.. not on a sled. Sounds like once your on the main your fine. where are your needles set? You have flatsides or kiehns on the that xc.? Try swapping your old can back on for a test. Have seen plugged exhaust do funky things. But again wot your ok... hmm
How did the midrange test go (zackattach) , wet or dry plugs?

 

[valleyml]

It could be a lean pop, actually on Saturday we looked at the ignition and checked all of the ohms test and they seemed to be fine. I was going for a ride on the same day and my mechanic wanted to make it more rich and see what it did......well it was about the same for the first 50 miles, then I stopped at a place for a few minutes, and then it was worse, backfiring even at full throttle. I'm going to try and lean it out a little and see if it will help. Thanks for the reply.

 

[valleyml]

About the midrange test, I never checked it the right way but when i took it from the house to the shop ( 3 blocks ) and then checked the plugs they were a little wet but not too bad, in otherwise they were not brown.

 

[hotrod]

Thats not far enough for the sled to be warmed up properly.