Jetting!!! Again and again and again!

[Glenn_KX500]

Why would I have to compensate with the needle position?
Isn't the surging due to the pilot circuit being lean?
What do you mean by sacrificing the idle, do I have to go so rich to get rid of the problem that the bike won't even idle afterwards?

[gowen]

Why would I have to compensate with the needle position?
Isn't the surging due to the pilot circuit being lean?
What do you mean by sacrificing the idle, do I have to go so rich to get rid of the problem that the bike won't even idle afterwards?

Glenn, I'm with you, I would have thought that the surging is due to a lean pilot. But, in this case, I'm assuming vacuum due to the mass of the piston. This really sounds stupid, but I've tried everything! I can get an idle with no surging, but end up having to get a longer idle screw. To completely eliminate the surging, it seems that richening the pilot mixture does not completely help, but bringing the needle a step richer does. They work together in this regard. But, you might have better luck, I was doing testing on the east coast at sea level and about 80-100 degrees. Now we are down to the 60s, but still crisp jetting and a little lean at times, but can always compensate with the air screw or needle clip.

A few of us folks that have chipped information about Jetting have all decided that the surging is a GOOD sign and means your jetting is just about right on.

Also, with the pilot rich and needle rich it effects about 20% of the power due to incorrect mixtures of the fuel/air. With that in mind, it's all up to preference, 20% is a huge amount, but the big KX already makes too much power, so most people don't care  . But, I like to squeeze every ounce of power out of my bikes and the biggest improvement in power is the jetting.

[KXcam22]

Hi Glen,
  Welcome to the jetting forum. Yes the surging is a bit of an enigma.  When your jettings lousy there is no surge, but as soon as you start getting close the surging appears.  I know it shouldn't surge but I'm not sure what the fuss is about (ok I know it's annoying but I just got used to it to the point that I forgot it does it - ask Gowen).  Mine is probably the worse offender I have come across but it doesn't bother me at all when riding. I suppose if you normally coast through corners it might be an issue, but its way more fun and the big KX loves a handful of throttle in the corner with a big wheelie out of it.  I do notice it coasting down mountain roads but then I don't care.  I know it's not much of an answer.  If you are willing to do some testing I would be happy to lend any advice I can. Two things I would like to test are intake volume changes and different carb types. Both tough to do. Cam

[kawdude]

Thanks for all the good information.  I think I finally tuned it in.

[gowen]

I have to say, the KX is a bitch to tune, but once tuned... wow!

[2kHondaCR500R]

You KX500 guys are not alone with having problems jetting the PWK. I have a 2000 Honda CR 500R I put a Sudco PWK 41mm Pro on and so far have gone down to a 45 pilot and still can't get an idle without the slide/idle screw all the way in and like 2.5 turns out on the AS. Anything over a 52 pilot and I have to hold the throttle open because it will not idle.

I find the jetting odd with the PWK 41mm needing smaller jets than my PJ 38mm, but I think it has something to do with the design and the PWK getting a better vacuum signal to the jets.

I have the DGH needle which I think is too rich in there right now on the 2nd clip. With a 52/172 jetting and 3rd clip it spooged out every connection in the exh system. It eventually fouled a BR8EIX plug too. I tried 52/170 jetting and still spooged, but barely got an idle with the slide screw all the way in and like 2.5 out on the AS.

I've got a few PJ carb needles (Honda part numbers) I'm going to try and I'm going to buy some smaller pilot jets to see what goes. I will keep you posted on that progress. I also got a N82P needle CROGG off ATM sent me from a KX500 I'm going to test out.

For now I stuck the stock PJ 38mm on and it runs fine with it set to 55 pilot, 4th clip on the stock needle, and 170 main.

[hoopty]

2kHondaCR500R, have you checked with Armpump over at CR500riders.com? He runs one of those PWK carbs and has it dialed spot on.

[2kHondaCR500R]

2kHondaCR500R, have you checked with Armpump over at CR500riders.com? He runs one of those PWK carbs and has it dialed spot on.

I haven't asked him directly, but anytime I post a "what is your PWK jetting settings" I get flamed with "no one bike will be jetted the same" and I do know that is true because of their porting, sea level, and mods, but I never got a base line to jet from over there because of that. It's all been trail and error for me on the PWK.

The jetting is too rich all the way around where I have it right now. Thursday I'll put the PWK back on, drop the jetting, try the KX500 needle, and the PJ/Honda needles to see which is best. I'll post back with results so we can compare how similar/different the CR500 is to the KX500 jetting.

 

[Timbowe]

Sounds like a trick machine you got there chap! You'll be hanging to get it sorted.

[Rotorised]

Having just read this whole thread it sounds like alot of hours have gone into jetting some of these bikes, reflecting on the time spent would it be better to take the bike to a dyno and get it tunned there?

[alan]

If the dyno was at the same altitude you going to be riding bike at!

I think dyno's are better suited for  looking a power curves and hp!

What would be nice would be EGT Exhaust Gas Temp gage so you could tweak your engine, just like you do in an airplane!

Alan

[Zee]

Hi All
   Here?s my stats; 2000 KX500, Pingel petcock, 5/16 fuel line, rebuilt carb, float height set to 16mm and verified with homemade fuel level tube thingey, clean air filter, pilot 55, air screw 1? turns out, DEF jet needle in the 2 position, 170 main, it?s a little rich for now, but will adjust after I get the idle/needle jetting right. Elevation 1400 to 2,000 feet, temp? My thinking at the time was ?I got the pilot jet dialed in so on to the needle diameter?. First it had a N89D, way too lean just above idle and way too rich between ? to ? throttle! Bike only ran good at WOT. Couldn?t find data on this part number so I switched to Sudco as they have a nice chart that explains what the numbers mean and at $5.25 a piece who would argue. They recommended a DGH; Bull?s-eye, HUGE improvement! Bike never ran so good but surging was also huge. As soon as I?d chop the throttle bike would go into the ?surge mode? maybe 15 times before enough speed was lost and the motor was back to idle. But I new I was on the right track as performance was unbelievable, (I hope you believe me). Next; 58 pilot. Way too rich at idle with 3 ? turn out on the air screw and it didn?t? help the surging at all; switched back to 55 and 1 ? turns out. Next; went smaller in the needle diameter from the DGH to a DGG. This cut the surging in half! That inspired me to again go to a smaller diameter needle. Only problem is no one makes a DGF, had to go with a DEF to get the next size smaller diameter. While this is one step smaller in diameter, it is also two clip position shorter in the functional L1 length. So what-the-heck I thought I would try it any way. Installed it in the middle position, (3), and went riding. Surging was reduced but not as dramatically as the ?DGH to DGG? needle change. Also caused bike to start running rich, (rough), in the 1/3 throttle range and a drop in needle position helped some but still feels like it?s too rich. Okay that?s where jetting is at today and I?m planning to drop the needle again to the one position, (hope it doesn?t need to drop further as I?m out of position). Are you still with me? My question is what needle are you running on your stock bike? Gowen and KXcam22 helped me out by answering a question I had in another topic, ?who makes custom needles?, answer; JD jetting. But what got my curiosity was a reply that I?m out there on the jetting and the fact that the direction I?m headed is running out of needles.

[gowen]

Zee, this is how I went about jetting my bike: #1...

Pilot-
Unscrew the pilot screw until I got most idle. If the airscrew was more than 2.5 turns out, I replaced with a smaller pilot jet. I did that until I got the maximum idle. Then I moved to the needle. I did that by the seat of my pants or.. dial a wheelie (most wheelie power 5th gear). If I was at the top of the needle, I'd go leaner, if I was at the bottom of the needle, I'd go with a richer needle. I kept doing that until I felt good about it. Then moved to the main jet. I kept going down until I got a CRISP rev when hitting the throttle. Also, until the smoke cleared. Take it for a few laps WFO. Keep going down on the main jet until you get that perfect hit,clean.

Continues next post:

[gowen]

Continued:

I drag race my KX500 in hillclimbs and drag runs. My KX surges pretty bad. That is normal! That is saying your jetting is right on. Don't worry about the surges. Cam and I have decided that surges are a sign of your jetting being close. I can say my jetting is perfect now, but it costed me a year or more to get it right.

Also a trick for the mainjet is to warm your bike up, do a FULL on wide open throttle test with a BRAND new plug. pull it out and look at the color. Brown is good, any grey or black indicate it is too rich. I pull my plugs out now and I have a hint of richness now, but mostly brown. NO black. But that is due to me running it rich due to the systems I am running now.

Good luck and let us know if we can help.

[KXcam22]

Zee,
 Sounds like you know what you are doing so it should be quick to dial your bike in sweet.  You'll know when you are there when the powerband suddenly get super smooth, the dial-a-wheelie and your bike will start 1-2 kicks hot or cold!  First some more data. 
  1. What is your average temp & humidity and you say about 2000' where you ride.
  2. What fuel/oil do you run and at what ratio.

 Also one thing to note is on the PKW39 the main and needle overlap quite a bit in the 3/4-full throttle range.  Before you can really get the needle exact you need to narrow the main jet down.  The 170 will be rich and will affect your needle testing as low as 2/3 throttle and up.  As Gowen suggests you would be best to get the main dialed before you proceed.   Then after we help you find the right needle it's best to do a double check on the main. Gowen's plug run advice is exactly the way you want to do it. I usually try to find a bit of a hill to put some load on the engine.  Also the surging thing seems to be a sign that your jetting is on.  Mine is the worst offender but I don't notice it anymore, I just keep the throttle mostly open all the time!!  The jetting chart is really close. I arrived at my jetting after years of tuning and it matches the chart. I would suggest using the chart setting as a starting point and then we can fine tune the needle.  I'll analyse where you are with the needle right now and post back. Cam.