They can do that if the compression is real low... if you've broken a ring for example. I know, it happened to me recently.

It can be so hard to diagnose these things without having the bike in front of you.

Always best to pull the plugs out first. The plugs can tell you a number of things. What condition are the plugs in? If they are black, then the mixture is likely to be crap, and will cause poor running. If one is very dry (with grey aluminium deposits) then it could be a failed piston giving poor compression. Can you get a healthy spark from both plugs? A weak (often pink) spark is going to point to an ignition problem!

So many things it could be I'm afraid.

Pop the plugs out, and pull the exhausts. Look at the condition of the plugs, and up the exhaust ports for any signs of piston damage. After that, it's a case of going through the ignition fault finder in the Workshop I would say.
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Andy.
NSR-WORLD.COM

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