It's the time of year for testing bikes it seems. On the commute this morning the bike began to feel flat at 4200rpm upward. It did this in 4th and 5th. It was especially noticeable on a steady throttle. There was plenty of go if I opened the throttle fully but on a steady throttle it feels like it wants to die but isn't hunting or cutting out. Bike idles fine. Brakes don't seem to be dragging. Chain is adjusted fine and in good condition as are Cush drive rubbers.
Weather is pissing wet.
Thoughts?

Coil and HT lead are where I'd be tempted to point an accusing finger first. Dry them out, seal them with silicone grease and try again.

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Yeah they were my first culprits. Will have a go tonight

HT coil and lead and plug cap checked for resistance and within tolerances.
Cleaned and greased and reassembled.
Will check valve clearances tomorrow but I'd be surprised if it's them.
Only occurred from 4200rpm upwards and in both 4th and 5th.
Due a 6k service ie no valve clearances but I'll do them to be sure. Air filter was ok, a little dirty maybe but not terrible. Plug was in good condition.
Hmm.

It's nothing to do with your welded up 'Y' pipe is it? Constriction in the pipework? Partial blockage? Welding debris broken loose, blown off and blocked baffles?

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...dodgy tank of fuel?

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HT coil came in on spec for resistance on primary and secondary windings.
Valves, inlet were slightly loose on one, exhaust was slightly tight on both.
Guess we'll see what tomorrow brings. For reference on the 25 mile ride back not going above 4000 rpm it was faultless.

what's the co like,

Just out of interest, what readings where you getting from your tps?? Im having very similar problems at the mo.

Cheers
Jon

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To boldly go where no Tenere has gone before.

right hand side of tank there's a little sensor with a breather tube coming from it (its you're manifold absolute pressure sensor) . when i had my misfire i went through everything from crank sensor,throttle position tests to ht tests everything u name it ... in then end i found if i pinched or took off and covered the hole it cured my miss fire ... replaced the sensor with a second hand couple of quid one and boom it was fixed when ever u held the throttle in a certain position or above it would miss like it was damp ... but pull her back and she would still power through it

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Yamaha xt660x 2009 blue/gold mods= iridium plug, stage1+2, removed snorkel, blocked ais, akrapovric pipes, power commander pc3usb (pre made map), adjusted tps, dynojet 02 optimiser 30amp aux relay, smoked puig screen, oxford heated grips and brembo carbon ceramic pads, rfx 30mm bar raisers, puig long adjustable leavers, plus much more and a cheep �30 alarm which stopped it been stolen