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My 1992 KDX200 while travelling at speed of 133Km/hr seized on me suddenly without any warning a few days back, causing the rear wheel to lock up. Luckily manage to clutch in to a safe stop. My first thought was bad gas due to prolong storage about 5mths fuel in gas tank or carb jets clogged up causing a lean seize. Pre mix was at 50:1.

Pulled out the jug, realized it was a 4 corners seizure.
1) cleaned out the carb completely,
2) refill the gas tank with fresh gas mix at 50:1 pre mix,
3) got a brand new spare cylinder on hand and install with brand new KIPs
4) installed std size mitaka piston and ring
5) new BR8ES spark plug
6) all new OEM gaskets
7) topped up brand new coolant
8) bottom end just complete service a few mths back

Today while breaking in the new cylinder on the final running in at 100km/hr I heard the engine giving out a rattleing sound and the kips valve seems reluctant to open up and there she seized up again. I must say that before this on the intial running in, the idilling is good and run very smooth at mid thorttle. Only at high rpm then came the rattleing sound from the cylinder which quit on me.
Pull the jug out and it is the 4 corner seizure again. Can anyone point out or share some experiences on this? thank you for any advice. I am also suspecting a overheating problem and check on the water pump impeller, it is rotating when I pushes down the kick starter.

Well, running a 92 200 at over 80 mph for any extended period at mixture rates of 50:1 is flirting with disaster. At high rpms all 2Ts suffer oil starvation when you close the throttle, and running at those speeds compounds the problem by also introducing higher cylinder temps than you normally see trail riding. Since 4 corner seizures are nearly always caused by too quick warm-up, too lean jetting, or too hot spark plug range I would suggest you address those issues. Easiest is of course to run a lower mix ratio and ensure you are jetted slightly rich. Of course that artificially dampens performance, but at the expense of reliability. These are not GP engines and weren't designed for extended operation at those speeds. There is also the matter of Mitaka pistons generally being considered to be no better than, or slightly worse than, OEM. You say you used a std piston, but did you measure your bore and piston diameters to ensure proper clearance? The one thing I can say is that 5 month old gas was NOT the problem. Someone else can chime in about breaking in a new jug/piston at 60+mph....I'd have difficulty believing that at that speed you'd be able to differentiate a rattling sound, and at any rate the KIPS would have opened much sooner (it comes on at about 6k)

bufftester wrote:Well, running a 92 200 at over 80 mph for any extended period at mixture rates of 50:1 is flirting with disaster. At high rpms all 2Ts suffer oil starvation when you close the throttle, and running at those speeds compounds the problem by also introducing higher cylinder temps than you normally see trail riding. Since 4 corner seizures are nearly always caused by too quick warm-up, too lean jetting, or too hot spark plug range I would suggest you address those issues. Easiest is of course to run a lower mix ratio and ensure you are jetted slightly rich. Of course that artificially dampens performance, but at the expense of reliability. These are not GP engines and weren't designed for extended operation at those speeds. There is also the matter of Mitaka pistons generally being considered to be no better than, or slightly worse than, OEM. You say you used a std piston, but did you measure your bore and piston diameters to ensure proper clearance? The one thing I can say is that 5 month old gas was NOT the problem. Someone else can chime in about breaking in a new jug/piston at 60+mph....I'd have difficulty believing that at that speed you'd be able to differentiate a rattling sound, and at any rate the KIPS would have opened much sooner (it comes on at about 6k)

Spot on IMO.

Bufftester is on the money , if i had to guess its the 50:1 mix .Way to little lube for the kind of RPM.

what oil are you running at that mix? is your bottom end bearing the source of the noise?

I am not too sure about the pre mix having any problem cause i have been using this ratio for the last 15years of riding this bike. As for the kind of speed at 133km/hr, it is not always i am doing that and did not keep at that speed for any longer than a few seconds.
I am running maxima 927 and am sure that it is not the bottom end and did check again. there is no free play up and down.
Think I have to do a complete recheck again on everything else possible. right now will have to wait for millienium to do both my cylinder and send back to me. heard they got good reputation for replating.

50:1, while OK for trail riding, is not sufficient to leave residual oil in the crankcase when ridden hard. So when you're at WOT and near max RPM, and you close the throttle to slow up (no fresh mix coming in), there is little to no residual oil in the bottom of the engine. Piston gets hot due to lack of lubrication, expands, 4 corner seizure. This is not surprising. Add to that that you were breaking in a new engine at over 100km/h using 50:1... I'm not sure what to say to that.

I would presure check the case and crank seals too. It they are leaking it will lean you out in a hurry.

Also,

How much residual oil is in the bottom of the crankcase after this happens? That right there will tell you if your 50:1 ratio is enough for the riding conditions.

Yes, i do have quite a bit of residual oil at the bottom crankcase after i pulled the jug. what does that tells you? pls advice.

Hi, I recently rebuild my KDX 220 because of a four point zeisure due to bad crank seals. Do the crank seal leak test first.

okie thanks will do the leak test.

If most of a full tank of fuel would be in those conditions I'd be running a 9 plug and rejetted for 24:1 mixture.