Maintenance & Technical > KX500 Original
Jetting!!! Again and again and again!
KXcam22:
I wanted to reinforce an old point: An important starting point for jetting is having your float level set correctly. Having said that and jetted many bikes I still had forgotten how much difference a small adjustment can make. My bike runs great but I was losing too much fuel out the carb overflows over rough ground. Float was set (as always) at exactly parallel. Strap a beer can on the overflows and you might be supprised at how much fuel is in there at the end of a rough ride. I once lost 1/4 tank with the bike leaned against a tree while I was eating my lunch (and not paying attention).
My Issue: Try to stretch out my mileage by preventing as much overflow as possible. For a trial I deliberately lowered the float level 3mm (from exact level) which is about 1mm below the min spec. Todays ride gave me almost no lost fuel and a crisper bottom end response. I was pleased at the crisper bottom end since I had noticed a gradual richening over time. I had suspected needle jet wear (ovaling) but couldn't detect any. Cam.
joebloggs:
Just finished a major nuts&bolts rebuild of the 500 hundred from the ground up.its an 89 model and every seal,bearing,gasket and just about every part that needs replacing due to ware and tare has been,only performance mods ive made are a gnarly pipe and hitech dual stage reeds,the trouble is know when i come to start it back up. Checked all all the jets and striped and cleaned the carb but found a 190!! main 62 pilot and a 1 step richer needle!!, what i cant get my head around is that the plug was a nice light tan colour and it started 1st/2nd kick and hardly smoked,it was on 60-1 putoline mx7.After reading the jetting charts i settled on a 170 /60 combination but left the original needle in,but now its a pig to start,wont tick over,smokes like hell even on the same ratio and oil and when it warms up it dies as if its either still got the choke stuck on,wich it hasnt or its running out of fuel,only thing i havent checked is the float height but how do you do it,do you need a tube and an adapter for the float bowl or is there another way? thanks for any help and advice,the forums been a big help over the last 2 years its taken to finish this bike,now all i wanna do is ride the thing!!
KXcam22:
Joe,
Welcome to the site! Next post mention your elevation, average temp and humidity, bike history and sparkplug type. Your original jetting was extremely rich. It is possible that the bike was resetted at one time to compensate for air leaking in the crank seals (I'm assuming that you replaced those). I am aslo assuming that the 89 carb is the same as my 92 PKW39. I think in the 87-88 years the carb float was different. The float can be set "eyeball" to level or you can blow into the fuel inlet and see what level the air stops (see previous posts for exact method). Level is the setting but I find it is better to run the level 1-2 mm lower (measured at center point of float). Since the bike is older I would check/replace the float valve. Any leakage will make it hard to jet. The richer needle and 60 pilot may give you some grief. The stock needle is on the verge of being too rich hence I run mine in the lowest position (clip highest). Have no fear. We will be able to get this thing running perfectly. Hope this helps. Cam.
joebloggs:
Bit more info but i think im getting close.Running at sea level at 5 to 15 c,b8evx (platinum plug),new seals in everything,carb is a PKW39,seems unchanged to later models and i think even though its an 89 frame its a 90 plus engine and even newer suspension(2000 on i think).Made a few changes to 55 pilot 170 main and found the float height was at 30+mm,no were near to 15mm to 17mm it shows in the clymer manual,no wonder it felt like it was running out of fuel,reset that and started in 2 kicks,wont tick over for long without reving it but its d**n close,close enough to bed every thing in for know,then ill stick it on the local dyno and get a fuel/air ratio print out and find out what it needs from that, Thanks for help KXcam22 and every one else on here.
FuriouSly:
Hey Joe... made my heart skip a beat when I seen the pics of your bike. Very nice looking.
Glad to hear the jetting is closer for you. You say that it is revving. Might want to check the reed boot for leaks/cracks and also the stator side crank bearing seal. Sometimes masks lean (you say 170 main and 60 pilot).
Sly
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