KX Riders
Maintenance & Technical => KX100 / KX85 / KX80 / KX65 / KX60 => Topic started by: 85#371 on March 30, 2015, 12:11:49 PM
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My son has a 2014 kx85 we bought the bike from Garrett marchbanks it has pro circuit cylinder carb and head the bike was set up to run mrx-O2 fuel and we swapped heads to run a cheaper c-12 fuel my son ran the bike roughly 15 hours after purchase and it started missing at higher rpm I cleaned carb,replaced top end,replaced reeds,swapped Cdi,stator,coil and it still had a miss on higher rpm' only thing left was replace the crank and that worked now 15 hours later it's doing it again I called PC today and they said it's because I used a hot rod crank and I need to use oem. I Connor keep putting cranks every 15 hours in this bike unless I get lucky and win the lottery. Any answers would be much appreciated
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Hot Rod cranks are the worst quality you can get.
My buddy was replacing them every 4 races in his kids RM80...and every 6 races in his YZ250...and they're only mid to front pack amateur riders.
Once they switched to the more expensive OEM cranks, he hasn't had any issues.
Try Wossner...I'm not sure if they make kits for the 85...but maybe our members Alward25 or Greenkaw24 can assist on that. Wossner is high quality from Germany...check them out...
http://www.wossnerpistons.com/
Have you done any wide open plug chops to be sure it's not leaning out on the higher revs?
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i brought a hotrod conrod kit for my 95 kx500, got it installed and built my bottom end but after buying a brand new cylinder decided to take it all apart again and remove the rod. i never ran it after everyone telling me that it would end up through my crankcase or worse my new cylinder. :x :x :x :x :x
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i brought a hotrod conrod kit for my 95 kx500, got it installed and built my bottom end but after buying a brand new cylinder decided to take it all apart again and remove the rod. i never ran it after everyone telling me that it would end up through my crankcase or worse my new cylinder. :x :x :x :x :x
EXTREMELY wise move :wink:
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i brought a hotrod conrod kit for my 95 kx500, got it installed and built my bottom end but after buying a brand new cylinder decided to take it all apart again and remove the rod. i never ran it after everyone telling me that it would end up through my crankcase or worse my new cylinder. :x :x :x :x :x
EXTREMELY wise move :wink:
+1
(http://www.oem-cycle.com/forum/download/file.php?id=2139)
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Have done plug tests using three brand new plugs and its definitely not too lean I'm going to da a compression test on it Friday and see how that goes if I was to guess it seems as maybe it's sucking air from the motor and leaning it out but it doesn't show on the plug I have the old crank from the first time and I'm no expert but it seems fine but after replacing it ran great
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I'm not an engine expert but it boggles my mind how the crank would be the issue what would the crank haveto do with it sputtering at higher rpm'a unless it's sucking air leaning it out not giving it enough fuel. I just know for fact I replaced everything and last ditch effort put a crank in it and ran great only for 15 hours though
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Nothing wrong with hot rods had one in my yz125 for 5 yrs racing now a local kids still thrashing it
More like its you crank seals leaking
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I'm not an engine expert but it boggles my mind how the crank would be the issue what would the crank haveto do with it sputtering at higher rpm'a unless it's sucking air leaning it out not giving it enough fuel. I just know for fact I replaced everything and last ditch effort put a crank in it and ran great only for 15 hours though
Have you checked and or set your float height?...it could be set too low.
Another possibility that I never used to believe, until it happened to one of my friends bikes...is the fuel cap vent. If it gets clogged, the fuel won't flow correctly...there's even some threads on fuel cap issues on here too.
Have you checked for excessive play in your crank bearings?
Does it smoke excessively when running?
**EDIT**
check the magnet on the flywheel for cracks or chips too.
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Have checked float height when we first got the bike it would leak fuel from overflow and we cleaned and adjusted the float.never have checked the cap or vent hose but will do Friday amongst other things that I will post. Thanks for your help
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Where did the "C12" head come from? P-C has a tendency to deck the cylinders, possibly your MSV is causing rod failure. Just thinking out loud here.
DoldGuy
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any one ask what oil ratio....just askin.
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Yeah the head and cylinder came from PC it came with a head made to run mrx-02 but at 30$ a gallon we got a different head to run c-12 from them.
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Symptoms of worn crank seals? Why and what would make it sputter at higher rpms that would be crank related?do these bikes have a keyway on the crank for timing that could be worn? I have the same bike stock that we can swap parts with if there's any suggestions. I would like to find the root of the problem instead of just throwing cranks in it every 15 hours. I don't beleive the last crank was bad neither did my mechanic that changed it. How to tell if there was a problem with the last crank? Maybe it was just seals and I didn't need to change the crank out?
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What is MSV? What about crank breather on the 85 could it be clogged I doubt it because we just put a new clutch in it before this happened this time and all the tranny oil leaked out and then we replaced it? I'm trying to think of all possibilities
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if it's not smoking excessively, then it would/could only be the mag side crank seal.
I had an '83 CR125 where the crank bearings were so bad, it allowed the flywheel to run out of balance enough that it messed up the "pick up", and would break up on the upper revs.
A cracked or chipped magnet in the flywheel can cause the same effect.
I don't remember anyone implying the crank itself was the problem, and I don't see that being the culprit...I myself would never run Hot Rod anything, just based off what I've seen over the years, and I would suggest a better brand regardless...
I think the Doldguy could be on the right track with the MSV(maximum squish velocity)...since the head was changed, then you started having issues shortly after.
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We had a hot rod let go on a kx 85 some years ago , broke at the big end side , lucky it happened at low revs and only cracked a case , and we could repair it , I stick with oem usually. Another thing I do to kx85 is to drill the holes that feed the main bearings 1mm larger as I had a problem there once ,seem to help it last longer , but I would look at the tuning side of things close, compression ,jetting , the casting behind the stator were the crank comes out ,were it dips in , they had trouble there to , is the crank cases sealed nice and tight.Hope you find out what it is , and don't give up on it , the cure is out there. Try a stock head , see if that helps?
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Cool guys thanks for the info. I never looked at the previous crank until today and had some guys from work look at it and it's in great shape so I don't know if it helps but the crank was fine the first time this happened why putting a new crank in fixed it I don't know but it did. I'm thinking that the seal between cases has a flaw and as time goes on it leaks just a guess. Let me know what you guys think. I'm off tomorrow and will be dedicating my day to the bike. Any suggestions I'm game. The other is the mSV makes sense kind of but wouldn't the bike do it right from the get go and not 10-15 hours later if that was the problem? I'll keep updating tomorrow throughout the day. Also shouldn't the compression be different with the head I have on the bike vs stock wich is 171. Will I hurt the bike running stock head with c-12 fuel for testing purposes?thanks guys
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Ok guys I had to get the bike done today so I went through everything split the cases inspected everything all looked good replaced crank seals and cleaned crank breather.replaced piston and did see blow by on the exhaust side of piston looking at the head I found there was only one pin stud in the head going thru head gasket found it in the mrx02 head don't know if that was the culprit but sure dindnt help matters any. Cleaned powervalve and carburetor put it together and it rips again hopefully longer than the last time. Thanks guys I'll keep you posted on how it runs in the future.
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good luck, definitely keep us posted.
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Just curious, what brand of crank seals did you use?
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Oem and all oem parts is all I'm sticking with for now and I did put the original oem crank back in it
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When putting the seals in did you use some lubrication for the seal lips?