Depends how you ride it. Like Andy says they're very rich std.

When was the last time you cleaned/changed those plugs? Or the airfilter? The service schedule is every 6 months/5000km for both items

Andy, my Rothmans didn't go too badly at either the Llandow TD or on our rideout and it certainly went a lot better than a stocker.
I fitted the stock '28 pipes when I first built it and rode it for about 3 miles. Absolute garbage, I had to stop to laugh at how bad it was.

It really depends what you want, the difference you can make on a '28 without swapping the PGM or running an HRC card is quite a lot, about 17bhp or just over 40%.
That's worth having, it's 2/3's or all you're going to get without taking the motor apart no matter what PGM you fit.

And way over 3/4's of that's in the pipes, most of it's caused by those washers and that's "free" to fix.

Basically a '28 with it's pipes opened up and the airbox modified is enough to keep up with other 60ish bhp 250's and 400's and they're fast enough to keep up on most vaguely sensible rideouts or with average trackdayers.
A stock '28 is not.
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