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After 35+ years away from riding 2 strokes I just picked up a pair of 1990 KDX200s. One is a basket case for parts and the other is a good running bike in need of nothing other than a new front rotor (which I have). To be honest, I have had a tiny bit of recent 2-stroke experience ...I own an old Yamaha DT250 -- but aside from running up and down the drive after working on it, it has been sitting and only occasionally ridden by a friend since I bought it 10 years ago.

But the KDX will be different. It will be ridden quite a bit this summer, and the little bit of riding I've done so far suggests that it will be fun. After horsing arouund a heavy DRZ400 for years, I have great expectations of being able to ride much better in technical stuff and single track on the little KDX. But much of the bike is a complete mystery at this point.

After just a short ride, I can tell that I will have plenty of questions for you all. I have done several searches here looking for answers to the basics like gearing, jetting, gas/oil premix ratios and common problems. Which leads me to this question: What the heck is the KIPS rattle? Is it some quirk that is common to KDXs? When riding it around the neighborhood the day I picked it up, I did notice what I thought was detonation pinging. I was prepared to ask if these bikes were prone to that, but I suspect what I may have been hearing is this "rattle."

Also, I live at 8200 feet above sea level in the Rockies. Is premium fuel recommended? And if so, is it required when the bike will never drop below 6000 feet? Finally, looks like different gas/oil ratios work for different folks, according to the threads I've read here. I want to run synthetic oil and was thinking that I'd mix it at 40:1, but some people here say to only run 32:1 -- which is what Kawasaki specifies. Without creating too much controversy, is it best to stick with the factory's 32:1 ratio?

Thanks for your advice.

First things first, welcome to KDXRIDER!

Yes, premium fuel is recommended. 40:1 is perfectly fine. What you are hearing is most likely KIPS rattle, although that noise that all powervalved KDX's emit is generally limited to low RPM. If you are hearing an increase in this noise as it revs out, I would run fresh premium mixed at 40:1 with a good synthetic oil (if the fuel in it is old), and if that doesn't help, check that piston to cylinder clearance is within spec.

Premium is best, it'd probably run on Kerosene (no kidding, these motors are beasts) 32:1 or 40:1 either works, key is to jet to one ratio and then stick with it (even more critical for you at such high altitudes). 32:1 will just generate a little more splooge to clean up. As Julien said, the KIPS rattle is usually most pronounced at lower rpms. At your altitude, I suspect some detonation at high rpm is going to be common if the bike is jetted stock. New fuel, new plug, fresh oil mix, clean filter and proper jetting should clean it right up.

Jetting help: http://kdxrider.net/forums/viewtopic.php?f=105&t=1156

Congrats on the new mount, and welcome to our addiction. You should be able to find the answers to all the questions you have right here. (oh, and btw, we're all visual folks who love pics! )

First, thanks for the quick and helpful responses. This seems like a pretty good group.

Regarding the possible sources of the rattle...My ear is still pretty sensitive to the sound of piston slap in a 2 stroke, as they are all I rode and raced as a young man (MX and Hare Scrambles during late 60s -- through late 70s -- yes, I am that old!). It doesn't sound like PS to me. I was riding the bike very conservatively -- because I was unfamiliar with the bike and also because I wanted to test its low end and mid range power. The rattle would occur whenever I short shifted (lugged the engine by getting into a higher gear early). So...Does that sound like the same noise?

My first goal is to get it sorted out...Make sure the fluids are right, spokes are tight, chain adjusted and the air filter is clean. Ride it a bit and establish a baseline. Once that is done, I am actually gonna dismantle the bike and swap the frame with that on the basket case. Why? Because the parts bike has a good CO title and I can then dual-sport and tag the bike.

Once I have put the bike back together, I will split my riding time between my porky DRZ400 and the featherweight (comparatively) KDX. I could end up forsaking the four strokes completely - or not liking the KDX. My guess is that I'll find both work -- for different kinds of riding. That means the bike will become the 7th member of the fleet in my garage.

Well, I am rambling...Thanks again for the advice. I look forward to sharing information with all of you!