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YZ450f lean condition

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People seeking some advice/direction, I purchased a 2008 YZF450 (70hrs) off a mate that was leaving the country (Western Australia) got it for a very reasonable price the bike had developed an issue being a lean condition, this condition had presented itself at just above idle, i am aware of this issue thru exhaustive research - thing is this is not your average lean condition that is well published.

This is the condition "bear with me", the condition is best described as when on the throttle lightly the engine backfires as in a lean condition.

More info: close enough 1000ft above sea level, Main 162, pilot 45, Needle NFLR set at 3.

Thing is i can shift the lean condition with adjustment of the needle eg: idle speed @ say 800rpm set the needle at 3 lean condition is at say 1000rpm....adjust the needle to 5 idle set @ 800 rpm lean condition presents at 3000rpm once again adjust the needle to 7 idle @ 800 lean condition presents @ 5000 rpm.
Have changed Main jet in increments up to 178 with no improvement, have changed pilot up to a 50 with no change, NFPP needle on back order.
Once over the lean condition or below lean (in rpm) the engine revs freely and with no hesitation.

 

What has been done: # new intake valves, new manifold boot, carb has been thoroughly cleaned and checked 3 times, exhaust repacked, manifold sealed, valve shims checked and rechecked, filter spotless, new jets, hot start cleaned as was choke all orifices cleaned with carby cleaner.....blown out with air.

 

This issue is doing my head in i have now come to an impasse, I have been reading ThumperTalk for a long period of time and know there is some very knowledgeable people on this forum i am hoping someone has come across this condition or has a "try this idea"

Cheers.

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Replace the worn out needle jet/emulsion tube and *maybe*  go to a richer Ncvs needle

There is a passage above the pilot jet with a very sharp bend that will not clean out with compressed air....you have to ream it with fine copper wire.

If the problem persists then you probably have a partially melted card body seal messing up the pilot circuit....that usually happen from using too strong a solvent to clean the carb.....

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Thanks for your thoughts THE KRAN, I have cleaned the passage as you suggested still no luck the lean issue still presents.

 

Have ordered the NCVS needle should be here in 3 to 4 days (needs to come from the eastern seaboard)

As I alluded to this condition presented itself before i purchased the bike the previous owner had done nothing to address the problem, so i am thinking partially melted carb body seal maybe? not.

I shall endeavor to continue to go thru the process of elimination.

 

If one can think of anything else no matter how big or small please let me know.

 

Cheers.

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If only it was as easy as that skorpan !, I have used all the settings on the needle with mains ranging from 160 to 178, been thru pilots from 40 to 55 all in various configurations with no change.

 

Electrical problem now I am of the belief as THE KRAN has suggested.

Last resort will be...a mate has pushed some trees down to clear his paddock, heaped them up i may yet fill it full of fuel get some strops lift onto the top of the heap and set the heap alight.

 

Problem solved!!.

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