Maintenance & Technical > KX500 Original
Intermittent high rev on my '88 kx500
bigbore:
--- Quote from: Friar-Tuck on October 24, 2011, 03:09:11 PM ---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/
--- End quote ---
hi all,
just an update on this, i stripped the carb and here is the spec of it:
the small stumpy jet is 175 (main jet?)
the skinny long jet is 45 (pilot jet?)
Needle has: NR1371 stamped on it and is on the 3rd clip down (or up) basically its in the middle
Havent been able to check the air screw yet.
According to my clymer manual standard spec is:
the 175 jet is correct,
but the 45 jet should be a 62
the needle code doesnt match
but the needle is on the correct cilp /notch
So from what i gather im running lean at the moment?
Is this right?
Oh and the other thing i noticed is that when i start the bike from cold, there is hardly any smoke out the back on it at all? And when you take off in first after just starting it and bring in the power, it doesnt have to clear itself like all other 2 strokes i have. What i mean by clear itself is that is doesnt splutter and blow a lot and smoke and then it comes alive.
i currently mix the fuel at 5 litres of petrol to 125ml of premix oil.
Many thanks for all the replies, much appreciated guys 8-)
Polar-Bus:
--- Quote from: bigbore on October 25, 2011, 08:09:42 PM ---
--- Quote from: Friar-Tuck on October 24, 2011, 03:09:11 PM ---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/
--- End quote ---
hi all,
just an update on this, i stripped the carb and here is the spec of it:
the small stumpy jet is 175 (main jet?)
the skinny long jet is 45 (pilot jet?)
Needle has: NR1371 stamped on it and is on the 3rd clip down (or up) basically its in the middle
Havent been able to check the air screw yet.
According to my clymer manual standard spec is:
the 175 jet is correct,
but the 45 jet should be a 62
the needle code doesnt match
but the needle is on the correct cilp /notch
So from what i gather im running lean at the moment?
Is this right?
Oh and the other thing i noticed is that when i start the bike from cold, there is hardly any smoke out the back on it at all? And when you take off in first after just starting it and bring in the power, it doesnt have to clear itself like all other 2 strokes i have. What i mean by clear itself is that is doesnt splutter and blow a lot and smoke and then it comes alive.
i currently mix the fuel at 5 litres of petrol to 125ml of premix oil.
Many thanks for all the replies, much appreciated guys 8-)
--- End quote ---
Your pilot jet seems way too lean. I believe I am running a #52 . Do some jetting searching and compare our jetting to yours. Try to replicate the weather and altitude conditions as well to ensure your jet change is going to be accurate. I believe my summer setup is 165 main, 52 pilot and stock needle in the middle clip position.
bigbore:
--- Quote ---Your pilot jet seems way too lean. I believe I am running a #52 . Do some jetting searching and compare our jetting to yours. Try to replicate the weather and altitude conditions as well to ensure your jet change is going to be accurate. I believe my summer setup is 165 main, 52 pilot and stock needle in the middle clip position.
--- End quote ---
cheers or that, im going to order a 55 and a 62 pilot and try them first. the needle (although it doesnt seem the correct one) i will leave alone and with the main jet.
The air is meant to be 1+1/2 turns out as standard so im going ot set that to incase its wrong.
il keep all of you posted.
thanks again.
IcemanK5:
I find changing to many settings causes more problems than it solves.
Try working on one problem at a time and see how the bike responds.
It least this way you can allways go right back and change it again.
Kurt
sandblaster:
Depending on the temperature I run a 58-62 pilot jet at sea level to 2000 ft.
The hotter it is outside the more mine tends to surge after riding for a bit and then idling.
Since my jetting is close to optimal when it does surge I just hit my kill switch for a second or two until the engine winds down, just enough not to kill it...
Also, depending on the temperature I run a 168-175 main jet and a stock needle at the 2nd position at the same altitude.
It's important to remember that surging is not pinging.
If it's pinging, it's time to worry... :roll:
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