KDXRIDER.NET

I am new to the site and new to KDX bikes. Within the last 3 weeks, both my boys and I bought one. We went from having 1 XR to having 3 KDX bikes. Mine is 1988, Nate’s is an 87 (that looks near new) and Ben has a 1993. We have put very little time on them at this point. Nate and I just got ours this week, brought them home and changed the oil, and gave it a once over. I did put new rubber seals in the exhaust on both bikes.
They all start and run really well.
I keep reading about a noise the KDX makes at idle, but the 87 and 88 make a godallful noise at mid to high range on the throttle. As soon as you shift up and reduce the load on the bike it stops until you get the RPMs back up. I know sounds are hard to explain, but it sounds like a clacking noise and I thought it might be bad bearings or timing off. I find it hard to believe two bikes do the same thing and I can’t find any info on this site about it.
If anyone can give me some directions on where to start, I would appreciate it.
Mike.

First thing I would check is the condition of the flywheels. They are a weak spot on those C series bikes and a very common point of failure. While you have the flywheel cover off you can also check for play in the LH crank bearing.

It could also just be the nature of an air cooled bike.

Thanks, I will check the flywheel and advise the condition.
Appreciate the advice.

Mike

Just in case anyone else runs into the same issue, I found the problem. It was the brass O-ring used as the exhaust gasket. I have a manual that shows the rubber O-rings but not the brass one.
Bottom line, it was an exhaust leak.