01-500, eng surges/pulses after run.

[John]

If you think logically; the ONLY thing which can cause any engine to fire with a closed throttle is that the engine gets air/fuel mixture anyway. The engine cannot fire without the air/fuel mixture. I don?t have idle on my bike (don?t? want it) so my throttle does close shut.

When I tweak the air/fuel ratio really lean the engine is less likely to fire - but it still does. This can't be caused by any leaks; its malfunction in the carb or just poor design since we all experience it more or less (including me). If it?s a serial fault, I would like to know what it is. I am suffering from this when I have the motard kit on and riding on tarmac. It's not so bad when riding in slippery mud mainly because I don?t notice it then.

I switched carb last year to the PJ (same as orderofsion) and the problem went away. Unfortunately, the carb I bought was cr*p, so back to square one. I have recently bought two additional PWK-39's which I will tweak and see if I can fix this problem.

//John

[jdv500]

well, thats another one of our many therories, and yes, we'd all like to know what it is, the problem- cause of surging. thought his site tons of owners of all yr models are having this big or small. we all have our own hunch on what it may be / can be. case seals, worn slide, kips valve worn or out of time and of course jetting. well it seems that this will continue to live with us as long as we ride this model we've chosen. unless we all join and hire a team from nasa and hook probes all over it. we've learned to live with it, cause the goods far outweigh the bads with our 500's. logically.  no worries. joseph

[KXcam22]

John,
  What is the basic difference between the PJ and the PWK carbs.  In particular is the slide the same shape or lots different.  I still feel the surge is caused by the PWK carb inability to hold back the big vacuum the KX makes. A different slide shape (PJ?) may be the answer. Cam.

[John]

Cam,

Check out
http://www.sudco.com/Diagrams323728/exppwk.gif
for the PWK and
http://www.sudco.com/pj_diagram.html
for the PJ.

If I understand things correctly, the PJ is biased towards ATW whereas the PWK is purely motocross.
The major differences are; on the PJ, the idle is adjusted by twisting the choke knob rather than adjusting the throttle, and the throttle is oval (not flat-sided). I am way out of my league if I could claim to understand why this would change the behaviour of the KX500. I am a computer nerd with a mechanical background.

I am sorry if I offended anyone. I do realise that there is no silver-bullet magic solution for this problem and I am not saying that MY ideas about this are the correct ones. I am merely participating in a discussion and applying my limited logical thinking capacity. No fuel = no fire. The problem might be related to the distance between the reeds and the piston? Or an inherited design flaw in the intake manifold ? really, I haven?t got a clue. My goal is to fix the symptoms and I aim to give it a go.

//John

[demographic]

I seem to remember reading that one way to give more power to a CR500 (which already have a PJ carb) was to use a PWK39 carb so would have thought that using a PJ would have been a backward step

Not used one so I am a bit in the dark about that.

[jdv500]

john ,
no problem, i've seen within this site that there are 1 or 2 guys that have never even heard of this run-on surging thing in their 500's,  nor did they know what the fuss was about. we love this bike and for me, i'll keep it forever or even get another to add to my arsenal.
earlier, you said that you prefer no idle,, i think that i know why this is,you use it for engine braking/decel.? also you said that you ride the 5 on tarmac.. where and when do's the surging happen out there, if ever.?, jdv

[John]

Jdv,

Same problem there - after full throttle a hard brake. With the grip on tarmac it is more noticeable; as in using the clutch not to loose the optimal track.

I am used to it but my friends are not. They usually just try my bike once.

//John

[KXcam22]

John,
  Yea I could believe that on tarmac the surge would be a bit of a bother, especially if you were leaned way over (dragging a knee?) decelerating into a corner.  Maybe a good reason to try a PJ.  I had one on an '87 CR500.  It worked very well with a similar engine and intake to the KX. Cam.

[demographic]

I am used to it but my friends are not. They usually just try my bike once.

//John

Aye, mine does it and the mate that I have let ride it hates the couple of Brang Tangs it gives out

I Ride mine on Tarmac but prefer it to idle as it pisses me off having to blip the throttle in trafic (especially if there is a police car about as they give the bike FAR too much attention as it is) cos it's a bit too loud.

[doordie]

Oki guys, I maybe have the solutions for the problem! :

This is my teory:

I think this is a KIPS problem.  
Every KX-cylinder I have tuned they all (1989-2004) have a problem with KIPS.
Either with opening or closing or both.
The opening it?s no problem with shims and new parts, but the closing.....
I have found out that KIPS is OVER-closed because of to short stopbolt(92066)
for the rod(49046) who is moving the KIPS.
When the rod moves too far back at low rpm, it?s opening the sub exhaustports
and let some "new" fresh air/fuel in exhaustchamber and it
ignite there,it?s VERY warm exhausts(600*) there.
I have no problem with surges/pulses, I always"take care"
of this KIPS problem.I put in a old steel bearingball and shims(92065) the stopbolt(92066) to right distance.
You have to take away your pipe and SEE (use flashlight) inside exhaustport how much distance you have to adjust.
And one more benifit it`s more lowend power because of right porttimes when the sub exhaustports isn`t engage at wrong time

IF you think I`m right here and you ALL people fix your problems with surges/pulses ,please send a little money($$) to PAUL(admin) so he can afford to
have this site still going!
(you can read about this in old post)

//doordie

[KXcam22]

Doordie,
  Thanks Doordie, I'll test out your theory on my bike. It surges worse than most and is due for a rebuild any day.  I'll check out the KIPS timing and see how far off it is.  Will be easy to tell the difference when I fire it up for break in. Cam.

[doordie]

KXcam22,
I belive this take care of the most of problem!
 
But do we have a good "electric man" who can
check more precise if our engines fires 2 times
each stroke?
Why I think that?
I have buyed a TINY-TACH and it show double RPM.
It suppose to read 1 spark each revolution and now
show twice.....

If it fires twice every revolution, my teory of the surges and pulses
come to MORE sense!
(I will explain later)

//doordie

[demographic]

KXcam22,
I belive this take care of the most of problem!
 
But do we have a good "electric man" who can
check more precise if our engines fires 2 times
each stroke?
Why I think that?
I have buyed a TINY-TACH and it show double RPM.
It suppose to read 1 spark each revolution and now
show twice.....

If it fires twice every revolution, my teory of the surges and pulses
come to MORE sense!
(I will explain later)

//doordie

Are you sure that you have the Tiny tach wire wrapped around the HT lead the right number of times? aparently if it's wrapped round too many times it can give a false reading.

[KXcam22]

Doordie,
  I'll put my new super oscilloscope on my ignition and see.  Is it possible your tach is seeing the coil discharge and then charge again.  Also in your KIPS theory how would jetting fit in?  Seems that for most the surge only shows up once the jetting has been leaned out.  It's completely melted here, ice is rotten.....and then it snowed 14". Cam.

[doordie]

demographic,

I wrap it 4 times as instruction describe.....I will test fewer wraps.
But I borowed a another tach(2 stroke)with crocodile jaw from a friend and
it shows the same double rpm,very strange.

KXcam22,
Thx mate, try your oscilloscope and see if you can figured out it.
By the teory, maybe with leaner jetting you get more fireable
air/fuel/old exhaust mixratio inside exhaust chamber,but I will "think" some more
and see if I get some another clue.

mun,my finnish friend,do you have a clue?

But IF we have twinsparker here, It?s  a solved problem!
 
Adjust your KIPS anyway guys and feel a right adjusted engine with
a huge grunt of lowend!

The weather is F....ed?up here too
one day cold ,next day spring with plus degrees.

//doordie