Backfiring mm700 , plz help

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burnoutink

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Nov 4, 2010
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Location
Whistler BC
I think I got Sled Issues,
So far my MM700, has been strong, but well traveling up the trail yesterday , i had it 10 mins before the middle cylinder started backfiring, ALOT. it continuously got worst, as i tested it. My solution as I was out solo was I took the spark boot off the plug, and made my way back to the truck on 2 cylinders, no backfiring popping sound. but when I hook the plug boot up to the middle cylinder she starts backfiring. I dont think I did any serious damage. I want to get this back on the snow asap. I'm gonna start with all new spark plugs, now its back in the garage. I'm asking for help from my friends at TY if there's anything I should look for??? or it any one has has similar problems??? Feed back is greatly appreciated.

Thanks
-Barrett
 
Check the centre cylinder for compression...it should indicate within 5 psi of the other two cylinders.
If the compression is OK:
-clean carbs
-change spark plug
-check your coil connections
-change plug cap
-check/replace reeds
-check for carb boot cracks/leaks

Keep us posted

Bob
 
Thanks Bob and Mike,
I dont know why I havent compression tested my sled yet, im gonna get a compression tester tomorrow.
really appreciate your input, gunk in carbs sounds about right.
the amount of riding I have been doing, it would not surprise me at all!!!

time to get at it so I can get back in the back country this weekend.
Thanks for the help I'll keep you guys posted, with lots of details.
 
YooperMike said:
Sounds like gunk in the carbs.
Click to expand...

I'm going with Yoop and Sideshows knee jerk reaction on this one. Is this the first cleaning since the 'preseason' cleaning.
Sounds like you've put a bunch of fuel through that bad boy this year. How many gal/litres do ya think.
 
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A couple of bucks said:
I'm going with Yoop and Sideshows knee jerk reaction on this one. Is this the first cleaning since the 'preseason' cleaning.
Sounds like you've put a bunch of fuel through that bad boy this year. How many gal/litres do ya think.
Click to expand...

Thanks Dannyboy, I bet your right!!!

600-800L, besides changing a spark plug on the same cylinder, this is my 1st issue. I can't believe I have to finally put it in the garage, I made it all season until now tearing it up, I'm impressed. Can't wait to open up the carbs and have a look inside, If Im gonna ride for the summer its time for a mid season tune up.

And we got snow still falling every day, Whistler Blackcomb says 2nd most snowfall in history, time to get this fixed ASAP.
 
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just putting the crabs back in here, and I got a stupid question.
what are these brown hoses coming out of the carbs, I didnt see where they attached to ,when I removed the carbs, any info is appreciated as its my 1st time removing and cleaning and re installing the carbs.
Thanks!!!
-Barrett

image002.jpg
 
vent hoses

they are vent hoses. the just hang into the belly loose. they allow air from the "atmosphere" into the carbs to get into the float bowls so that they are set to the correct pressure. I believe this is their function. they just hang down. some people on some machines try to connect them to the airbox, but I never have done this. I was also wondering if you found any stuff in your carbs. I am considering cleaning mine today. I cleaned them well at the begining of the season, but will still ride for another month. just my 2 cents
 
Mine did the same thing last Friday, all it needed was a new spark plug.
 
Crank Seal

Suprised No One Has Said A Crank Seal Yet. Only Way To Check Is A Visual, Leakdown Test, Or If You Are Brave, (dont Recommend) Spray Carb Cleaner At The Seals With Engine Running. If The Rpm Increases Or Changes You Have A Leak.
 
Carbs surprisingly werent very dirty at all, thank god I got 2 sets, 1 set had 12/12 screws stripped on the float bowl. (probly why the sled was sold to me for 1500$)

Still... working away here, definnatly some sort of mis-fire, still lightly back firing(not as bad, still center cyclinder)
-its not the carbs
-its not the spark plugs

-replacing all spark plug boots tomorrow
-serious inspection is gonna go down, now I finally have some free time.

Thanks for giving me an idea of what to look for, with my issue.
Seriously, with me being new to engine work I really appreciate it!!!!

Can't wait to find this Backfire Gremlin that lurks in my Engine!!!!!
 
Before I drove mine into a tree, I put these on and replaced the wire. Not so sure I needed to replace the wire, just did it anyway. Are your coils up on the airbox or mounted down where it's warmer/hotter. My 97 was up at the top of the airbox, I cannot remember what year they changed the mounting location. Have you swapped coils to see if problem follows ?
 

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