Top end Sputter

[sixstring4137785]

Here's the deal.
00 KDX220, FMF rev, Boyeson reeds, Modified airbox lid, 42 pilot, 145 main. Running 40:1
I've been riding on this setup for about a year with no problems. just a good clean powerband from right off idle to screaming top end. The past two rides were decent except the fact that my bike developed a little sputter around the top end of the powerband. I tore down the airbox, the carb, and the reed cage, replaced the reeds, inspected and cleaned everything. The new reeds refreshed the throttle response but that sputter up on top is still there. I tinkered with the jetting but the results showed it was properly jetted before i messed with it, and it was only adding confusion to the diagnosis. I keep the insides of this bike super clean and use only high quality fluids in an attempt to avoid an early top end service. any suggestions before I move on to the powervalve and top end ?

 

[Mac]

Have you tried a new plug? Even if it looks good I would change it before playing with the top end.
It's been pretty warm here in New England the past few weeks, did you try a leaner main?

 

[Sage]

do you check the compression? if the plug dosent fix it then i'd be looking at a compression tester set.

 

[fishhead]

When I was running that setup on my 220 I found the 145 main to be a tick rich in warm weather. I suggest trying a 142 with a new plug, I had best results with a br7es, you can check the kips for full operation by removing the round plug on the riders left side of the engine just ahead of the subport chamber cover. some have reported that not using a resistor plug can cause a high speed miss. Hope that helps.

 

[David Trustrum]

Other things to check sparkplug cap & coil + earthing of same.

Assume you did a total fuel & carb cleanout?