[Aussiecrf230]

Try opening the idle mixture screw a quarter turn.
It does seem strange that it is ok at idle and WOT, almost like you ended up on the wrong clip position.

[JimDirt]

1 other thing on the carb , have you replaced the Needle Jet (this is the long tube that the main jet screws into and the Needle goes into) , if it is worn it will cause all sorts of issues from idle changing from one minute to the next , to rich and lean conditions , especially when you have the needle on the 5th clip position , maybe try putting the needle on the 4th position , and/or replacing the Needle Jet (it should be around $8.00 u.s.)

You will not be able to really see any wear , but what happens is it will oval out and make the needle gap change without moving the throttle itself , this will cause the carb to run rich then lean without even touching the throttle because just the vibration of the engine running will bounce the needle around , so you could come into a corner and it will just richen up or lean out and stall

Not saying this is it , but its one more thing to eliminate and is relatively inexpensive

[scotsy]

After a 2 week break from struggling to cure this misfire I am ready to try and solve it again. I made this short video to show exactly what I mean. It started 2nd kick after a 2 week break and when warmed a little will tickover very steadily and will rev quickly to the rev limiter but anywhere in between the extremes it misfires really badly.


http://www.youtube.com/watch?v=idxaVTwA ... tube_gdata

[Spectatoruk]

Hey Scotsy,

I bought a CRF450R 2003 model only two weeks ago. It seemed to run ok when i went to view, but on my first outing yesterday it just kept dying on me at low revs.
I am way behind you on the fault diagnosis, but I sent a pm to Ken who replied with

1. JD Jetting kit
2. Replace the floating valve seal
3. Replace the hot start nut with an aluminium version, as the stock plastic one gets worn or broken it results in a hot start that is stuck open, leaning the mixture.
4. Verify/set the float height
5. Replace the header gasket.

I like you have really been phased by it as it seems there are just so many/too many variables to work through. Plus, I am no mechanic, I would normally be taking it to someone like you to sort out!

Let me know if you solve the problem because whilst mine is popping rather than misfire, it could all be linked, especially the stalling at low speed issue.

Good luck mate!

Mark

[scotsy]

1 other thing on the carb , have you replaced the Needle Jet (this is the long tube that the main jet screws into and the Needle goes into) , if it is worn it will cause all sorts of issues from idle changing from one minute to the next , to rich and lean conditions , especially when you have the needle on the 5th clip position , maybe try putting the needle on the 4th position , and/or replacing the Needle Jet (it should be around $8.00 u.s.)

You will not be able to really see any wear , but what happens is it will oval out and make the needle gap change without moving the throttle itself , this will cause the carb to run rich then lean without even touching the throttle because just the vibration of the engine running will bounce the needle around , so you could come into a corner and it will just richen up or lean out and stall

Not saying this is it , but its one more thing to eliminate and is relatively inexpensive

Hi Jim and Mark, I have today spoken to a UK distributor of Keihin parts and asked him about my issues and he is 100% confident in Jims suspicions of the needle jet nozzle tube being worn. The company is www.allensperformance.co.uk and I have bought jets etc from them before for other bikes but never previously asked for help with a problem.

With a bit of luck this will turn out to be the cause of this mysterious misfire and the new nozzle and main jet will put an end to it when they arrive.

Wish me luck and I will update this thread either way ............. now where did I leave those matches?

[JimDirt]

Great , i hope that is it and it solves your issues , keep us posted !!

[scotsy]

nozzle is on back order Doh!!!

patience is a virtue (but I want it NOW)

[scotsy]

UPDATE

'Jimdirt was spot on with his diagnosis'


After waiting since March for the #27 needle jet nozzle to arrive (it was on backorder from Keihin) it arrived yesterday in the post!!!


I am pleased to inform all of you who offered advice that the bike is now running as it should be since fitting the new nozzle #27


Thanks for all of the help, it was a difficult thing to find unless you have experienced it before and even yesterday I actually doubted that this new part would cure it .................but 'cure it' it did!!!


Cheers


Ian