Honda VTR250 'slight' misfire up to about 3-4000 rpm

[robkblue]

Hi,

Can someone with some mechanical savvy offer any sort of diagnosis on this issue.

This 2004 model Honda VTR 250 has a misfire going on up to around 4000 rpm. Brand new plugs were put in and after only twenty kilometres the plugs were pulled and look like the ones in the attached photo. The dirtier one with all the deposit is from the front cylinder.

What could be going on, sorry not very experienced mechanically and this is not my bike. The owner thinks that both are getting spark.

Thanks,

[robkblue]

Sorry, here is the picture, for some reason it did not insert into the first post.

https://ibb.co/kMp8pH

[Fozzie]

I'd try the ignition coil driving that spark plug first, it's often the cause of a lot of mis-fires when they begin to fail.

[leener]

Any, and I mean 'any' problem is solved by a process of elimination.

So long as you understand the combustion engine, you have some idea on where to look.

If it miss fires then on stroke three, the plug likely isn't igniting. And, if you have put new ones in then I would begin with checking the leads and the coils. Work your way up from spark plug to battery until you find the problem, and avoid spending a single penny on any parts until you're beyond all doubt of what the problem is.

I learnt to fix all my vehicles from being on this forum and it helps if you get a Haynes manual to give you plenty of facts about the bike, such as coil resistance and about the wiring loom.