Bike Jittery and Optimistic Speedo
 

Hi All,

Got the bike yesterday, love it!

This evening we went for a leisure ride up the mountain and back and I noticed the engine is somewhat jittery at idle speeds, say if I hold speed at 60 the bike feels like it sputters with a faint rocking feeling.

It's the same feeling I used to get on the KLR when I ran out of fuel and I had to open the reserve tap.

Second thing, when I do about 100kph on the dial the GPS indicates about 85, this seems way out. Is there a way to recallobrate or fix this?

Thanks in advance.

This sort of feeling is symptomatic of the hoops that Yamaha had to jump through to get the motor through emissions regulations; basically it runs to lean on small throttle openings when the ECU is running in the closed loop. It's pretty easy to fix with one of Kev's O2 Controllers, which fix the air/fuel ratio in the closed loop to 13.6:1. Fitting this will give you an extra 1000rpm of useable power below 3000rpm and stop the jittery feeling.

Read this thread: http://www.xt660.com/showthread.php?t=20381

Unfortunately they are all like this - about 10% optimistic. The choice is either to get used to it (10% is easy maths), or fit a Speedo Healer to correct it. The downside of the Speedo Healer is it puts the speedo right, but the odometer will end up under-reading by 10%. Basically you can't have your cake and eat it! ;)

Read this thread: http://www.xt660.com/showthread.php?t=8876

Thanks so much for the quick and detailed reply!

That is such a relief.

I'd rather have it be a standard issue that a second hand problem.

It doesn't bother me too much so I'll keep riding like this for now, but may consider the O2 Controller later.

At least it's not a mechanical problem.

I think there may be another reason my speedo is out by so much (checked today, 135kph indicated, GPS reads 115kph) as I noticed today at 130kph GPS my revs sit at 6000rpm so I read on another forum a guy with the same speed and revs as me at 130kph but he has a 14 tooth sprocket instead of the factory 15.

It seems the speed is read somewhere from the gearbox and if you change to a smaller sprocket it will affect your speed reading as well.

The speed sensor does indeed read off the gearbox output shaft. Changes in sprocket, tyre or rim size will alter the reading on the speedo. In fact under and over inflated rear tyres will effect the reading too.

I should have said the speedo is about 10% optimistic in "standard trim" in my earlier post.