Maintenance & Technical > KX500 Original

Kick-backs for dicussion...

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John:
Hi all,

Problem for discussion:
After I have revved the engine a lot and let go of the gas I get these nasty kick-backs from these single massive 500cc explosions. As opposed to what could be called two-stroke engine break..?

Cause?
I suspect this is caused by the fact that the engine is suffocating, i.e. not getting enough fuel. Baring in mind that this is low revs, I figure the problem is caused by either the pilot jet or the air-screw or something I have totally missed out?

Solution:
I?ve tried to re-jet the pilot jet to 64 (latest). I have changed the float level (pisses fuel even when tilted 10%), changed the reed-valve. Almost everything except changing the carburetor itself. The only result so far is a total lack of idle and - the kick-backs persist. I have not tinkered with the ignition timings or spark-plugs. The bike always starts and behaves in all aspects except this one.

This is really starting to annoy me :evil: When it happens, it kind of pushes me out from the ideal line in the slower curves (more so on tarmac than on gravel). I am using the clutch as a workaround to cut out this effect.

I know others in this forum have similar experiences on their KX-5's BUT does anyone have the solution :?:

/John

Paul:
Hey John, those kick-backs are a sign of loading up. The 64 p/j is a big pilot. What happens if you jet it with say a 58?

John:
Paul,

Yes, been there done that... with a 58 pilot jet the bike idles and the kick backs are more frequent (if it makes sense?). I have changed the jetting up and down but I get the best result when it's rich. The drawback is no idle but what the hell, who needs idle anyway?

It approved somewhat after a top-end overhaul I did recently. The previous owner had two top head gaskets. I just have one of the new slim ones = higher compression ratio.

Question!
Am I the only one who is experiencing this? I talked to another KX-5 rider here in the UK and he had the same problem. Please tell me that there are more of you out there who have the same KX-5 behavior as I do. I do want it to be a KX-5 problem rather than a ?John? problem?

/John

Paul:
Did you have the bottom end pressure tested when the topend was done? If not look behind the flywheel and see if there is any sepage from the seal. Sounds like you maybe sucking air in from the dry side seal and causing a lean condition. This would explain the need for the big p/j and the surging.

John:
Paul,

Thanks, nice one! I'll check it out tomorrow in the daylight.

Cheers,

/John

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