KX Riders
Maintenance & Technical => KX500 Original => Topic started by: quartertondiesel on April 27, 2014, 11:43:19 PM
-
Hi guys,
Just picked up an '88 KX500 recently and am pretty new to the big bore stuff, they sure are different animals. I've read a lot on surging with this bike and have had this issue already (had an air leak, replaced intake boot, problem solved) but am noticing now that the surging has come down to a reasonable level. Now, I am noticing a very repetitive mid to high stroke when the bike idles almost like a bucking sound. The motor is brand new (top and bottom end) and is now broken in, the previous owner swore by running 91 octane with Castrol super 2 at 32:1, which seemed to run fine as the motor broke in but now it does this bucking... I have just mixed myself a fresh batch of 91 with Amsoil Interceptor synthetic at 40:1 and have noticed a huge difference in the bike's behavior. However, it still seems to buck somewhat and doesn't always come back down to idle after cracking the throttle when in neutral, it really is completely random.
I have been told just about everything... from running a higher octane to not bothering with synthetic, also have been told to possibly try a thicker head gasket? I have been told to run it rich and run it lean, some people run 32:1 and some run 50:1... like I said, kind of new to this bike so anything can help right now!
Also, I have added a stealthy flywheel weight to the bike so I'm guessing that might play a factor in why it won't always come down to idle from a high rpm?
Thanks for the add!
Regards
Rick
-
some surging is normal on the 500, depending how your jetting is set-up...this can play a role in how excessive the surging can be. There's a ton of threads on here about surging issues. To be on the safe side, you should do a leak down test 1st, and be sure that you're not sucking air somewhere else and causing it to run lean.
-
+1
And, while your poking around, what altitude are you riding?
Pilot jet size?
Main jet size?
Needle number?
Clip on the needle position?
-
I had the carb apart not that long ago and didn't think to write any of the jet sizes down but from what the previous owner had told me the carb/jetting was factory. I ride about 580 ft above sea level and it's rather flat out here so not much altitude changing. Unsure what the best jetting would be for my situation? I'll have to run a leak down test soon, but thanks for the response guys.
-
Get your air leak fixed (If you have one( then look at 55/168 3rd position on the clip.
-
i had the same probleme in the last 4 weeks... replaced the old carb-holder and my ´86 engine runs now again like a swiss clock with a very little surging that all kx500 do... (except the factory-engines :wink:)
-
Thanks for the info guys, I'm anxious to tear down that carb!
-
what type of riding are you going to be doing for the most part?...i.e. track, desert, woods/trails.
-
All woods and trails for this monster
-
I had a 2002 KX500 street legal that surged so bad that it was nearly impossible to ride at highway speeds at a constant RPM. I tried jetting, checking for air leaks, KIPS operation, etc. I tried a flywheel weight which "seemed" to magnify the effects of the surging...I was about ready to give up on trying to dual sport on it, though it was tremendous to ride off-road. Everyone has their theory of what makes big-bore two-strokes surge (ie. mixing of burned and unburned gases, intake pulses, exhaust pulses, combustion chamber design, blah, blah, blah blah). I researched all types of engines and their operating conditions and one consistent cause for surging always seemed to be found: a constant or TRANSIENT lean fuel condition! I had tried all kinds of slow, main & needles (PWK 39) to no avail. My k5 had an FMF Gnarley & a RAD valve, and was geared pretty high 18/47 (don't ask!). I noticed that the big KX motor, going down the highway at 50-60MPH, was spinning pretty fast but required hardly any throttle to do it. I stumbled on to an Italian Keihin distributors web site who showed that a PWK is much more sensitive to the slide cut-away and over a broader range, up to half the the throttle opening according to them, than say a Mikuni. I called Carb Parts Warehouse in Cleveland and they suggested slide #4 or 5 instead of the stock #7. I went with the #5 and IT WORKED! It went from unrideable to taking 50 to 200 mile trips; could have went farther if not for the seat & the vibration. You'll have to rework your other jetting because it richens the mix everywhere, and the fuel mileage suffers--mine dropped to 33MPG on the highway (measured!) but with my 4 gallon tank I could safely go 100 miles between fuel stops. Another unexpected benefit was that it pulled much harder off idle. With my tall gearing I had to slip the clutch a ways to get it rolling; after this change you could let out the clutch and roll on the throttle and away she'd go! I hope this long post will be helpful to some of you--this problem was maddening.