01-500, eng surges/pulses after run.

[jdv500]

HELLO,
NEW TO THE SITE,41 YR OLD RIDER. Kx PROBLEM IS THIS; I'VE JUST BOUGHT A VERY CLEAN AND SEMI-FRESH 2001 KX500, AFTER ALL THE FLUIDS AND FILTER CHANGES, I PUT FRESH GAS AND OIL IN IT AND WENT FOR OUR FIRST RIDE.
** AFTER ALL RUNS OF ALL SPEEDS, I CLOSE THE THROTTLE AND COAST ALITTLE, BUT THE ENGINE SURGES AND BUCKS THE BIKE FORWARD 3 OR 4 SMALL TIMES, BEFORE IT WILL ACKNOWLEDGE THE SHUT GAS AND THEN IT WILL MELLOW OUT ON IT'S IDLE...
IT DOE'S IT REAL BAD IF I DO A HIGH SPEED RUN AND CHOP THE GAS ,(CLUTCH-OUT) AND COAST, THE BIKE SOUNDS AS IF I BLIPPED THE GAS REAL FAST 3 OR 4 TIMES, BUT I DON'T- IT DOE'S. AND. WHY IS THIS, PLS. NONE OF MY PAST BIKES HAVE EVER DONE THIS,, KX'S AND KTM'S...
THANKS, jdv, sorry for caps.

[gowen]

Hi, welcome to the site, I will start by saying mine does the same. Just like you describe. I believe it is normal for the big KX due to vaccume. You might want to do a search on jetting, you will see that it is pretty normal and I've done ALOT of research in trying to rid the KX of surges and to get an idle.

[neverendingmods]

My new 04 500 does the same thing.  The jetting thread and some others(surging) put my mind at ease.  I thought for awhile my throttle was sticking.  But no, it's just the big cylinder firing. Excess gas and the air vacuum I guess.  Only does it after wide or near wide open blasts.  The only bike I've owned that's done it too.  My only big bore.  

[KXcam22]

jvd500,
  Hope thats a "KX" problem (KY problems are kind of personal-HA HA).  Yeah just as everyone has said that surging is normal.  Mine probably does it worse than most but is not an issue when riding.  Take it a a sign that your jetting is pretty close. Welcome to the site. Cam.

[04kx500]

I've had three 500's since i was 17 and i'm 36 now and so far and my 04'kx500 does it to , consistency is a good thing. The first (85)and last(04) make a almost knocking noise that i have learned to ignore, some do and some dont. I tore enginge and split case on " 04" at  4 hours and replaced rings,upper bearing and clips cause i was there and  nothing was found abnormal anywhere.
eric 04kx500

[jdv500]

hey there,
after looking around within this great site i've learned alot.!! what to worry about and what not to worry about concerning my surging and run-on...
 during the past week or so, i've went out and bought a new pipe, higher octane gas, diff main jets and pilot jets, and a new air filter. ** i have installed them all and will ride today. it's been really cold and wet and windy here in north alabama. but it looks as if today can and will be test day as it's cleared up greatly. , i'll write back afterwhile, joseph

[kawdude]

My 94 has done the same thing since day one.  The best combination is having the jetting correct.  If you can dial in the slow jet you should be able to remove "most" of the surges further by adjusting the air screw.

[machine]

My 04' KX5 dose the same too.

Must just be a KX5 thing!!!!

[demographic]

Yep, my 90 does it also
Which can be a bit disconcerting for mates having a bash on it

Especially considering that mines set up for the road and in Supermoto trim.

Kind of revs up with a BRANG then off the juice with a TANG, Tang, before the revs come down.

A mate got off it and sait that he had much more respect for me as a rider getting it to go so fast and still between the hedges as it can lift a bit on WOT

[orderofsion]

I'm a bit late replying but for what its worth my kx used to surge then I bought another carb off ebay (it was cheap) , since then the surging has stopped completely . the old carb was a pwk39 and the new one is a pj39 otherwise they have the same jetting .

[kawdude]

I tried a new carb too and it did help but not totally.  Someone suggested that an airleak or bad slide could cause the surging.

[gowen]

It all has to do with jetting. If the jetting is slightly rich down low, the surging will leave or clear up. But, running through two carbs and two KX500's here locally, it is pretty d**n normal. I did get ahold of a 41mm PWK carb from Pro-Flo and it is JUST the same after jetting the low-end to perfection. Nothing has changed even with a new carb, it is just as bad. Which does not bother me now, did though, like hell it did.

[jdv500]

hello, it's been 3 months since i posted this surging thing above. i've installed a ton of mods, maint parts and dress-up goodies on my 01. i'm very happy with it but even after the new top end and having the kips valve completely cleaned , mic'd and reinstalled, it still has the same ole' pulsing, right at the end of some hard throttle. i 've jetted, 54/165, response is instant. i see here within the site that roughly 9/10 owners have come to terms with this kind of issue.
**** if i had to make an educated guess at it; i'd say that it's the exhaust gases right out of the flange and the reverbing air flow in the chamber that are trying to get by each other, sending a false signal to the valve actuator in the process- via the last-in-line exhaust air just entering the valve........like an accordian/ ripple, this is just me............i've heard all the other hunches, is in ; case seal leak, carb slide worn, pilot jet too +/-, reed valves or boot cracked, valves out of timing... but even after we've cleared all these up, us and the some new 04 owners are saying the same thing. like you all have said above, we have learned to live with it or grown accustomed to it, i don't even think of it at all now adays when i ride, the bike has tons of great qualities to enjoy, but it did sound a bit odd to hear my bike as i was watching a home video of me on the bike.
 thanks and enjoy...

[hughes]

May be hard to compare the two but my 87 500 use to do the same thing. But after 1 size smaller main 1 size smaller pilot and lowering the needle jet one slot. my engine will just wine down to idle as the bike slows or if I roll off to a lower speed it runs fine. I changed the jetting just to clean up the throttle. When I first rode the bike before jetting I can just wine out 3rd and back down off the throttle the bike would surge and seem like it would surge forward. Have you lowered your needle jet How is your idle speed set :I have my idle speed set as low as I can get away with. With the throttle rolled back to idle after a high speed run, I think the only air that is going to enter the engine will be under the slide and with the idle mixture screw. I think the only fuel the engine may get is going to be through the pilot jet. There may be a fine line here with the amount of air and fuel vers. piston speed. I think what I am trying to say is the slide hight(idle setting)and air mixture screw turns in or out ,after rolling off the throttle may let to much or not engough air to mix with the fixed amount fuel going through the pilot jet. Man it's getting late going on 1 a.m I hope some of this makes scents.

[jdv500]

thats sounds like good stuff there.
my idle is set just enough to keep it running barely, just as yours. my needle is 2nd clip from the top. i have to admit that the surging is alot less then when i first got the bike. and not really an issue now adays. even if it's still present. your right with what your saying there, i thought that with the slide down all the way, just a crack of day-light at the bottom to allow air to mix with the pilot jet then into the reeds. your thinking this may be the source of the problem.?
* up kinda late on a work night there huh.? thanks... joe