kx85 SPITTING AT MED TO HIGH RPM

I have a 04 kx85,  at about the rpm the power band is about to fire up,  The bike starts spitting and sputtering..  


It has 140 lbs of compression
New crank.
I have cleaned the carb and new filter.
new plug
Reeds are clean and in good condition.

I have not looked at the power valve, but I did take the power valve cover off the side of the head and looking at the side of the head the valve looks like it is opening up.

If you have any clue why it is spitting, please sputter me some info!!

Thank You!

Ron  

Welcome Ron!  Was the crank just installed??  140 lbs comp is kinda on the lows side for something with a new crank. unless the ring wasn't done then. but anyway, did u just get the bike?? did it just happen all of a sudden??  what ratio do u use? what plug? what jetting du u have? anymore info u got would b great.  

Hey,Thank you for the welcome!!  
 I have had the bike for two years.  And It was running really strong!
I am not sure when it actually started messing up,   It is my sons bike(10yr old).  So I can't tell you if it was a sudden thing or gradual.
It starts up very good and runs good until this rpm is reached. Bam no power!  so He is unable to get a hole shot


I use Maxima 927 oil and mix it 32:1
I have tried two different plugs br8es and a br10es.  
The  crank was just replaces this summer and I think it was doing this before the crank was replaced.  
The carb,  I cleaned it very good and have not done any jetting work.  It has factory jetting.  

i guess it couldn't hurt to pull the power valve and take a peek.  do u have the manual??  

can u run the bike with the PV cover off and c if it opens under acceleration??  

Yes I do have the book,  That would prob be a good idea to break the valve down and see  if it is ok....   I have taken the side cover off and reved it up a few times ,, the valve does appear to  open up.. Or at least the rod and lever do there thing, I cant see the valve with out breaking it down,,

But You did give me the idea to take the cover back off and run it and see if I can look at the valve opening at the same time it messes up,,,,,  

I do mean running it down the road  

Pull the ignition cover off and check how clean the stator is,it may be only generating enough current to cope with low revs and then as revs rise the spark gets weaker.

 Could also be the coil breaking down under higher load.  

ronqqq:
I have a 04 kx85,  at about the rpm the power band is about to fire up,  The bike starts spitting and sputtering..  


It has 140 lbs of compression
New crank.
I have cleaned the carb and new filter.
new plug
Reeds are clean and in good condition.

I have not looked at the power valve, but I did take the power valve cover off the side of the head and looking at the side of the head the valve looks like it is opening up.

If you have any clue why it is spitting, please sputter me some info!!

Thank You!

Ron

Is it spitting and sputtering like its rich and loading up, or cutting out like its starving for fuel?

Have you pulled the plug and taken a look at it?
.  
.
Dave H 2006 YZ250
(2008 YZ 125 son)

M D..  I was thinking maybe a firing prob is possible, I have a buddy that has a full bike in a box,  Going to do some part switching see what happens..

DLH..  It would almost seam like the loading up at the high RPM, but I just dont think is a fuel prob.    Plug is a little tan,, I like to see them a little on the black side...  

Its the wrong plug dude!!!!!!!!!Buy a NGK R6252K-105......its a race plug the one from the factory(in the manual)Thats why theres no top end power ronQQ  
My sponsorships Winners do it in the Corners!

Prob solved!   I had an FMF pipe on it since it was new,  I put the stock pipe back on and it came alive.  
Not sure why,,  I cant see much build up and the packing is still in pretty good shape.

Thanks for all your help!
Ron  

I'm going to say that your main and needle jet needed adjust for the fmf pipe.  
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DIABETES SUX!

Well we put the FMF pipe on when it was new 2004,  It ran good until now. So I am guessing there must have been some carbon buildup in there where I could not see, that might have caused it to maybe need some jetting..   But anyway the original pipe did the trick.  

Thanks for your help!!  

good