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Discussion Starter · #1 ·
Okay I have a 04 mxz-x 800 and I was riding the other night taking an easy at 40 mph when the sled lost a cylinder. I was out in the middle of a field near no roads so I started it and if I got on it the sled would clear up till I let off the gas. now after trucking it home it will not do anything but fire on mag side backfiring like crazy with no power. changed plugs then wires then coil. it has 135 wot compression on both cylinders (3 pulls) I went through the carbs exhaust valves sprayed carb cleaner around crank seal its not bad its getting fuel. still doing the same thing! im stumped on this one im going to test stator and trigger coils when I get home but it has spark!!??? Any suggestions??
 

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Discussion Starter · #7 ·
I pulled the reed cages there good but how could the crank be out of sync? its been running good prior to this put over 1000 miles on this season. If I put new plugs in it it will run and idol for a minute then start backfiring. Sometimes it seems like pto side has weaker spark. its always pto side not firing correctly the plug gets wet.
 

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Discussion Starter · #9 ·
I went through the carbs on it checked the pilots and everything float seems normal as the other float. how do you check for proper float height? Can the main brain make the sled run this way? Can a trigger coil off set the timing ?
 

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While the carbs are off, check that the slides are both opening since the linkage can fail and only one will lift then.
 

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Discussion Starter · #11 ·
I checked that while the carbs were on the motor with the air box off. Both are opening evenly. This thing has me stumped....
 

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1 thing u could possibly check is:
I had the carb needle retaining clip come loose once so the needle was bouncing around in there flooding it out. Easy to check
 

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Discussion Starter · #14 ·
If it was the stator or trigger coils wouldn't the sled not have spark? I have a feeling this is something electrical
 

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Thoughts on spark.
Know that it takes more energy for the plug to fire under compression. So the spark you see is not what is happening in the cylinder.
Good idea to check the stuff down on the crank. Inspect all harness connections.

The coils on the crank have more than one failure mode. Not digital like on or off, but analog like somewhere in between. The electronics work on voltage levels to create the energy to produce spark and when to initialize the spark. If there's an internal short it effectively changes the length of the windings. This then changes there output level and thus thing don't work right.
 

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Discussion Starter · #17 ·
That's what im in the process of doing now. the startor seems to test right between yellow/ yellow yellow/green and yellow/green should be a resistance of 0.0 to 0.5 ohms and yellows to motor 0.L and im getting 240 ohm out of trigger coil wich its supposed to be 190-300 I believe which is good but I have a cheap multi meter and don't have the vdc "voltage direct current" setting or cant figure out which one its supposed to be on my mulit meter to see what voltage the trigger coils putting out.
 

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You say you have spark go to Napa they have a spark tester you put in in line to check strength but you said you have spark if you do its carb as because you said you have compression
 

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Discussion Starter · #20 ·
yeah it has spark and great compression but I've gone through the carbs. everything checks out. I haven't checked the retaining clip on the needle I will when I get home but it runs like the timings off. backfires hard. but if the carbs good I don't understand what could be causing it to do this unless the mpem can cause it or I have a wire somewhere shorting outwhich I have looked for but its hard on the revs because or the plastic cover around the whole harness! lol
 
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