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02 mxz 800 runs very rough

2002 mxz 800 renegade fouling plugs rough rich

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#1 Axel751

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Posted 18 January 2021 - 11:05 AM

hey all, first post here and probably a long one but im hoping for some help before i start losing hair over this sled. little back story, i originally bought this sled (02 mxz rene 800) about 6 years back, had a fresh rebuild on it at the time but i was dealing with what i assumed was massive over oiling issues, ended up changing the check valves on block oil lines and cleaning carbs etc all the basic stuff. still fouled plugs like mad but pulled like a freight train. ended up selling the machine and through dumb luck this past fall i wound up with it in my possession yet again.

 

skipping forward to now, it sat for a while and didnt run, as i was working on it, i ended up having to replace the carbs as a broken mix screw was found on one(happened with previous owners) and replaced oil pump with another used one and set properly including return spring mod so its not to stick open. ended up with a set of hooded rev carbs running original needle(9zly2-58), 17.5 pilots with the 520N mains. took it out for a test it idles OK and runs super rough on acceleration and i could not pull more than 6k rpm and still super oil rich, sounded like it was blown. i checked comp 140mag and 145pto.

also did some research and found with hooded carbs leaner jets are needed, dropped down to a set of 420s. now when i honk on it, its very rough accelerating(ALMOST like its running on one lung) but once on the very top end it clears up and can pull full rpms and starts to sound healthy again. but from idle up to top its just trash.

 

its hard to tell on a brand new set of plugs and being oil rich how the fuel is but something just doesnt seem right to me. im hoping someone can chime in and get me pointed in the right direction. 

 

thanks


Edited by Axel751, 18 January 2021 - 11:05 AM.


#2 TugHill800

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Posted 18 January 2021 - 11:38 AM

Have you had the reeds out? Do you think it’s all engine or are the clutches dirty or beat? What plug are you running? How does it start cold? Warm?


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#3 Axel751

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Posted 18 January 2021 - 11:57 AM

feels totally engine related. also the primary was replaced with a brand new unit back when i owned it the first round, the old damper split, but everything is moving as it should and is still super clean. now that you mention the reeds, im not 100% sure but i heard the kid that bought it from me had brought it in to local dealer, supposedly had reeds replaced, along with plug cap and wires replaced(i had to redo wires as someone tried gluing in the wires). im not sure what else was touched while it was gone.
i can also add that when i did the oil check valves, i had also performed an engine leak down test to check integrity of bottom end seals and that all tested good. cant remember if i had the oil pump off or not though to see if inner seals leaked on crank.

 

 

ill check out the reeds as you suggest; hopefully some time today.


Edited by Axel751, 18 January 2021 - 12:02 PM.


#4 TugHill800

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Posted 18 January 2021 - 01:23 PM

Try also grabbing a set of br9eya plugs it’s not gonna make that much of a difference but they do have a little better spark position.


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#5 TugHill800

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Posted 18 January 2021 - 01:37 PM

Just do a quick look at your plug caps and wires maybe you have something starting to show itself there as well


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#6 Axel751

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Posted 18 January 2021 - 11:08 PM

okay so that was one issue i was chasing as it seemed to have weak spark as well, checked out whole ignition system checking resistances and output etc and someone had changed plug wires and caps before me, i found that they siliconed inside where the wires go into the coil as they wouldnt stay in due to chunk of old wire around the spike, cleaned it up, got all silicone out of coil and trimmed the new wires. got awesome bright blue spark and ignition is tickety boo. i should also note im running br9ecs-5, and tried a set of eya's too. none of that made a difference on the lack of performace though.  i am highly suspect of the reeds as well for the performance side. and possibly inner crank seals for the oil issue as i cannot seem to find any logical reason for the over oiling. 



#7 Ditchbangr zx

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Posted 18 January 2021 - 11:41 PM

If your getting that much oil, might want to check the condition and clean your Rave valves! Might be wise to do another leak down test as well.





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