Misfire at 2000 RPM

Seanyr · Post by **Seanyr** » Sat Apr 06, 2013 8:19 pm

Have a problem with my 2003 BCR. It misfires at 2000rpm no other time.

It has no CAT, Laser cans with chip (from new), Lennies induct, KN filter.

I have set valve clearances, cleaned air filter, replaced plugs, balanced TBS still no joy. About to change fuel filter. Grasping at straws, grateful for any ideas???

Cheers

Sean R

South_Oz · Post by **South_Oz** » Sun Apr 07, 2013 12:35 am

With all those mods it might be running lean? Do a plug check maybe.

I would get rid of the K&N myself. Any air filter you can see through isnt going on my bike.

Dave

Seanyr · Post by **Seanyr** » Sun Apr 07, 2013 8:52 am

Thanks Dave,

Top plugs look lean, bottom rich?? Might have to experiment with airfilter. Why only misfire at 2000 rpm, any ideas??

Sean

slparry · Post by **slparry** » Sun Apr 07, 2013 8:56 am

coil sticks in the dual plugs aren't there? Could it be a coil stick breaking down?

Dai wiskers · Post by **Dai wiskers** » Sun Apr 07, 2013 11:36 am

slparry wrote:coil sticks in the dual plugs aren't there? Could it be a coil stick breaking down?

+1

Seanyr · Post by **Seanyr** » Sun Apr 07, 2013 8:07 pm

Thanks for the tip. Is there an easy way to diagnose save changing parts on spec?

Sean

slparry · Post by **slparry** » Sun Apr 07, 2013 8:36 pm

can you tell which sides misfiring?

Seanyr · Post by **Seanyr** » Sun Apr 07, 2013 9:49 pm

Would be guessing, will have another go tomorrow.

Sean

Dai wiskers · Post by **Dai wiskers** » Sun Apr 07, 2013 10:15 pm

If the bottom plugs look rich i would think thats where the problem is, but i am often wrong also i know next to nothing about twin spark models so this could be common with twin spark models

However if there is something common to both bottom plugs thats where i would start looking,

Another thought 2000 revs if it had carbs i would say check the air screws and needle jet but we cant do that here, so start with the big brass screws on the throttle body's 1-2 turns out from just seated not tight, set right hand screw to 1.5 turns out then set left one the same adjust left one in or out up to half a turn till motor smooths out [easier if you have vacume guages but not impossible without] then screw both in or out equal amounts untill you get a tickover of 1200

Check that there's not a piece of grit or dirt on the cable guides behind the throttle bodies this will often cause rough running

oyster · Post by **oyster** » Mon Apr 08, 2013 3:36 pm

Others here have switched plug leads, top and bottom, to test for coil failure. If the sooty plug moves with the coil, it might be the culprit. On old bikes, this misfire was usually points failure. My 2l car had a weak coil pack that only showed up on the diagnostic, did not notice it while driving.