im fixing up a cbr for my brother to race at thruxton in october but having a bit of a nightmare with it running.

-I have cleaned the carbs, float bowls were clean when i took them apart
-running standard jetting and set up
-new plugs
-nipped 5mm off each ht lead so fresh lead showing
-new fuel filter

It starts and idles ok, sometimes it can get a little lumpy idling but its intermittent. sometimes when riding it will pull nicely up to 9.5k then just bog and feel really flat, as if its dropping a cylinder. sometimes it will pull through but it will really struggle and lurch as if its cutting in and out of 4 to 3 cylinders.

Now today i rode it, it was riding as above for first half an hour, but then it started pulling clean through if you accelerated from low revs.


occasionally it will drop to 3 cylinders at very low riding speeds then pick up 4 at about 4/5k revs

Any ideas peeps

Coil breaking down?

tanuki wrote:Coil breaking down?

possibly , ive got a few spares kicking around, so i'll give it a go

Check the wiring where they plug into the loom under the air box as well

i fitted a new set of coils, worked good for the first ride pulled through, still a bit hesitant in 4th gear up after 10k revs.

but then next ride it was back to normal, i've just cleaned out the carbs again, checked all the diaphrams and everything was all ok.
It rode different again once i put it back together.

Now has a tiny flat spot at 8k then pulls through, will rev to redline most times in first 3 gears, but in 4th gear upwards once it hits 10k it starts hesitating feeling like its cutting in an out on once cylinder, either fueling or spark but ive checked all this over about 6 times now. at a loss

I think its new loom time, they are not exspensive and will take you about a day to fit.


God knows though, could be anything from CDI - TPS

Good luck

Yeah I've got no problem fitting a loom, made my race loom for my zxr.

Sticky valve??? I had the same issue on a GSXR400 of mine and it had a valve that was sticking according to the mechanic...

that was my next direction, checking compression etc

no need anymore as my brother got tired of it not being fixed so bought another cbr 400

so now i can give the shit one back to my mate aha

Haha problem solved then!!