power loss

The other day while riding I noticed that the bike felt under-powered to the extent that i though i was accidentally in 2nd gear when I was in 1st. Its is less noticeable when up the rev range but I suspect its suffering the same loss throughout. I also believe the noise of the engine is more 'raspy' deeper almost but not in a good way. I've also notice a mild increase in vibrations. It has remained the same or possibly become worse over the last few days. It may be getting hotter quicker too.

When home I took the tank off and checked the pipes that attach and all appears well. I balanced the carbs and put the baffle back in my exhaust (fuel.) I checked the K&N filter and its looks a little dirty but not too bad. 

Both down pipes are hot so i'm assuming both cylinders are firing. I couldn't see any holes in the pipe work either.  It idles as good as always and has no problem starting nor dying when riding.

Its due for a minor service ASAP as last major was done 4000 miles ago. However I'm not convinced it will fix the problem.

Something is definitely up and I'm worried that my engine is going to fail or blow up mid commute! 

Can anyone shed some light on this please?


 Should i stop riding it work until fixed?

Been there. Done that, observing 'noises' or other perceiveable anomalies, leading to thoughts about 'what's wrong?'.

Take a minute. Deep breath. And then, disregard your paranoia and fallback into 'logic mode'. Most symptoms DO have a logical explanation.

Raspy noises, easy starting, power loss, both cylinders firing. Let's see...

Easy starting, both cylinders firing. Neither carbs nor ignition malfunctioning.
Raspy noises. Hmmm again.
I'm not experienced with eg. conrod bearing faults or broken pistonring symptoms, so I'll fallback to asking a simple question:

Oil? Amount and age...

And while you're at it, check for 'glittering' metal filings in the oil.

On second thought; just change the oil. THEN look for 'glitter' in the discarded oil.

The oil level is around 3/4 full, 4000 miles and maybe 7 months old. i know some bikers insist on changing oil sooner but the manual says at 8000 so I though it should be fine. I sucked some out the engine to have a look and it seems normal dark ish brown but not black. Im no expert though.

Thanks for the advice SB, I changed oil spark plugs and oil filter and now all is back to normal. 

Seems like the oil was the problem as the plugs are in good condition. I filtered the oil with a sieve but it didn't catch any dirt/metal. 

So does anyone change their oil at the recommended 8000 mile intervals? If not when do you decide to change??

I wait the full 8,000 miles because I do a lot of miles, and also because I'm a cheapskate. Can tell it's getting knackered by the end of that, gear changes aren't so smooth, and it gets difficult to find neutral.

I doubt my bike would be very happy if i left the oil change to every 8000 miles. I guess that is to do with the relatively short journeys and stop/start nature of riding in london.