Maintenance & Technical > KX500 Original
Intermittent high rev on my '88 kx500
Philthy Phil:
could be that your throttle cable needs lubing?
bigbore:
--- Quote from: Philthy Phil on October 23, 2011, 07:54:46 PM ---could be that your throttle cable needs lubing?
--- End quote ---
no i already checked that and it has enough freeplay on it.
Friar-Tuck:
Hey BigBore,
Yes it seems the engine gets caught in a lean burn on decel and bucks or surges. Usually at the least opportune moment, like wanting to slow down to make a turn. You get a "mmpow mmpow pow" and get pushed farther than you need to go!
I don't recall anyone claiming to have any engine damage due to the condition.
The remedies vary from a new or different carb, to fatter jetting to a kips bolt mod.
I'm sorry I can't give you a better answer. The bike seems to have a lean burn condition when the jetting is close to optimum.
The engine draws in just enough of an air/fuel mix through the pilot circuit when the throttle is chopped and the engine is decelerating to burn lean instead of Idle down.
Sorry I can't be of any more help than that.
Tuck\o/
Polar-Bus:
--- Quote from: bigbore on October 23, 2011, 03:10:12 AM ---hi all,
ive noticed a intermittent high rev on my kx500 when im out driving it. i recenty fully rebuilt it and have only been out a hand full of times on it.
when im driving along in any gear and pull the clutch in, it revs itself as if i was turning the throttle about a 1/4 turn. it sometimes stops and just idles normally.
also if im driving along in any gear and let the throttle off fully and let it roll in gear it does the same high rev thing and i can actually feel the engine pulling the bike with the intermittent high rev - as if its driving itself.
its wierd??? - ive cleaned the carb and air filter - no difference.
only mods are boysen power reeds, reed spacer and decompressor mod i got done by larry.
Someone sait it might be an air leak somewhere??? Maybe i niped a gasket that letting air in???
its not loosing coolant or oil, doesnt over heat and stall or cut out and still has tons of compression.
I cant be sure if its running the power it should as its been doing this since i rebuilt it - never drove before rebuild as i bought this as a project. and ive never driven any other 500's.
the bike pulls well and has lots of power, powervalve seems to come in early compared to other 2 stroke ive had. however i recently sold my Yamaha YZ250 2 stroke 2006 and that had way sharper, violent power almost felt faster than my kx500 ?
im looking for some help and advise on this matter from you experts,
cheers guys,
bigbore :-D
--- End quote ---
Unusual engine revs are a lean condition. The challenge is to find out where. A good place to start is the intake boot and reed cage. The other less common possibilty is some overly lean jetting. This is where a seasoned "ear" helps. Listen to the engine as it revs, then pay attention to exactly how the engine behaves thereafter. A lean air fuel screw will cause erratic low speed and idle behavior, a rich air fuel screw will cause the engine idle rpm's to slowly decrease and load up the engine.
ZETTNORCAL:
load up. yes. after it is shut down even for a few minutes, then restarted it feels just like I started it up cold with the choke and have to blow it out before it runs clean again ........ sorry for the lingo...
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