Sorry to hear it was a scam, Pierre.

There are a number of clues to a bad MC21/28 centre seal, but the two most common are a difficulty to start, and a poor/erratic idle.

When riding, the RPM will often "race" when the engine is at normal operating temperature too, and won't settle down unless a little load is put on the motor. They generally run very poorly lower down the rev-range, and sometimes struggle to pull through the RC Valve transition range (around 7000-8000rpm). They can however appear to run very well at high RPM, so don't let a seller try and fob you off by saying "the bottom end just needs a bit of a tune"!

Of course all the above depends on everything else being in absolutely tip-top condition. I.e. battery/charging system, fuel system (fresh/clean fuel), air filter, top-end (piston/rings), and last but not least, correct jetting. There is no reason whatsoever for any NSR not to pull right from the bottom-end all the way to 11,500+ without a single hiccup, regardless of tune. Even a full-on 70hp+ HRC spec F3 will pull flawlessly to the redline if it's in top condition.

The above also applies to the 1989 MC18 R5/6K, as it uses a similar crank/centre bearing.
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Andy.
NSR-WORLD.COM

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