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2005 MXZ 550F Carb/Electrical Issue??? Sounds like it Misfires?

550f MXZ 2005 Misfire Carb issues timing poor mileage

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#1 bschwart

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Posted 12 February 2021 - 03:30 PM

Hey folks need some advice.  Been fighting an issue with my 2005 MXZ 550f all winter. Had the coil pack replaced a year ago due to starting issues at a shop.  Apparently had low spark...  Also they rebuilt the carbs. After that ran ok but it ran out of gas on the wife at about 60 miles.  Tank was full when we started.  Move to this year.  It now starts on a couple pulls but it sounds as if it's misfiring or loading up on fuel.  Not really sure.  i put in new plugs.  One turned black the other stayed almost white.  I put in a carb kit, new jets, needle, seat, etc.  It still doesn't run correct.  I have just started it in the garage after the carb rebuild but sounds the same. Almost like it's missing. I checked compression.  About 115 on both sides.  I've read this may be ok but there is not a common answer for this motor.  Some say it needs to be at least 125psi.  I used a gage from the auto shop.  Not sure how accurate it was.  took about 5 pulls to get it to 115psi.  What's your thoughts?  Is there timing that needs to be set?  Motor rebuilt?  I'm just about done with this thing and the wife is saying just sell it and she wont ride. Any help would be appreciated.  I would really like to get this thing running correct.  It only has about 1800 miles on it and looks brand new.  Thanks!



#2 SPOCK

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Posted 12 February 2021 - 03:58 PM

I doubt it needs a rebuild, those motors are tough and they don't have high compression anyway. It is possible you have contaminated fuel, it may be necessary to remove the fuel tank to dump it all since water will settle at the bottom. Also make sure the intake boots aren't cracked at all. Finally, a leak down test might be done to see if there are any bad crank seals for example. There isn't any timing to set that I know of.



#3 stealth bomber

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Posted 12 February 2021 - 04:26 PM

Sounds to me like the choke plunger is sticking open in the carb on the side with the black plug. 



#4 SPOCK

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Posted 12 February 2021 - 04:28 PM

Good call bomber, that is a common problem with those old cables.



#5 bschwart

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Posted 12 February 2021 - 04:38 PM

Thanks for some ideas.  When I rebuilt the cards I adjusted the chokes by inserting a drill bit.  You could feel them both move and just past half towards full choke the bit would go in further.  Should I just adjust them so they are down as far as possible?  Basically  so there is no choke operation?  They seem to be moving ok.



#6 stealth bomber

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Posted 12 February 2021 - 06:36 PM

I use a pen light and look down the choke circuit from the back of the carb. Adjust the cables so the plungers have half the circuit open when the choke is on half. This basically mimics the go/no go gauge skidoo has to do the adjustment. Perhaps you have something else going on like a leaky needle and seat. The black spark plug is the issue IMO.

#7 stealth bomber

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Posted 12 February 2021 - 06:39 PM

Just re read your original post. Could the fuel pump be leaking into the crankcase?

#8 bschwart

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Posted 12 February 2021 - 10:31 PM

Thanks Spock and Stealth Bomber......I'll check these suggestions out next week.  Thanks for all the input.  If anyone thinks of anything else let me know.



#9 bschwart

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Posted 22 February 2021 - 05:33 PM

Just wanted to update on my issue.  I readjusted the chokes by looking in the carb and setting them half way open at the 1/2 choke position on the lever.  At first sled still ran rough but smoothed out after a bit.  Took it out for a quick 10 mile ride around the lake,  It ran good, didn't sound like it was missing so going to say its good to go.  It also had terrible fuel mileage of about 6 mpg.  Unfortunately I may not get it out again to determine if that problem improved also after the carb rebuild.

 

Thanks Spock and Bomber for the tips!!







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