New Guy Old KDX

[etard]

Hey guys, first post here, great forum, it took forever to get accepted on for some reason...

I have a 1987 KDX that has been plated for the street (no small feat considering the process in California), I bought it like that so I could ride up to the fire roads around Big Bear Mt. I was thinking of selling it because whenever I rode it around Barstow ( Stoddard Wells) it would always lag when I needed it to move. Well, after riding it at a lower elevation I figured out it was not properly jetted for that elevation. Barstow is about 2000 ft. higher than where I was riding last weekend outside of Palm Springs. Now I absolutely love this bike, it has more than enough power for me, throttle response is great and it is as reliable as my dog.

I have been reading a lot, and learning alot here over the last few days and it seems I can upgrade the Carb, so my first question is:

Can I just plug n play on the Carbs? I am thinking of getting an extra one with jets for higher elevation, and keeping the one I have for lower. Wouldn't it be easier to just swap carbs rather than jets every time?

My second question is:

If I were going to just swap jets, how would I figure what I need? I believe Barstow and much of my local riding (Big Bear) will be between 3000-5000 ft. Is there a formula or calculator somewhere?

The only thing is the bike runs great as is, and I don't want to mess it up by messing around with it. If it ain't broke...

Thanks for any help guys, I love riding this bike and felt a real bond to the community last weekend as a fellow KDX owner motored past me as I was trailering my KDX, he gave me the nod and I gave him the thumbs up, I think that was all that needed to be said. :nod:

 

[jb_dallas]

I wouldnt mess with it unless I had to, especially being an older bike. Apparently, jetting is a trial and error method for each bike...as you can read in my thread.

 

[etard]

Thanks JB,
I did just read your thread and I also just read the JustKDX info on Jets. WOW!! I'm not really that patient to swap in and out jets, change clip position and all that jazz, but I guess once you get it right, then the work is done. I would almost rather pay a tech to put in the proper parts and then test it out one weekend, but if it's not right, then I might as well have done it myself. It's kinda hard tuning for higher elevation, the only way to really do it is to go out there I suppose.

 

[julien_d]

lol, I wouldn't mess with it?

Jetting is probably the single most important tuning you can do for your bike. I would mess with it, and I would mess with it a lot!

If you're going up in elevation, the air is less dense, so you will need less fuel, so you need to go down on the jet sizes. Probably 1 - 2 sizes smaller for the elevation change you're talking about. Get yourself a range of jets. I'd check what jets you have and then get 1 larger and 2 smaller for both the pilot and the main. This way you will have a range to test with.

There's a jetting guide around that will walk you through it step by step. If you go at it methodically, and jet each circuit individually, you will find success and happiness :)

J.

 

[etard]

Hey Julien,
Thanks for your input, that is exactly what I was looking for, a basis to start experimenting. I will look into buying some needles this weekend at Chaparral Motorsports. I decided that you are right, jetting is an important skill to have so I might as well learn it now since FI dirtbikes cost nearly $10K.

 

[jb_dallas]

Julien

Earlier in the thread, the man just said he is "not really that patient to swap in and out jets, change clip position and all that jazz" and you are telling him to go experiment with jets. One could laugh at that advise as easy as they could my advise to leave it as is.

 

[etard]

JB,
I don't think he meant any offence, it's just a differing opinion. Some people live to ride and others wrench to ride. I'm somewhere in the middle :) I like to ride and enjoy the pride of ownership when you rebuild your forks or get the carb tuned right and everything works better, and you can feel the difference. It's a great feeling no doubt. Other times you just wanna be able to kick that motor over and ride away, absorbing the scenery, not worried about how your bike is riding. You feel me?

 

[reepicheep]

I found a table somewhere... My conclusion from it was that you may have to switch one size in the jets between summer and winter riding. The clip probably should move as well.

Swapping jets is probably about the same pain level as swapping a carb, maybe even easier. Loosen clamps, rotate carb, remove bowl drain bolt thingy (for main) or 4 screws and bowl (for low) and swap the jet without moving the carb. I got to where I could do it in 5 minutes easy on the side of the trail. Pulling the whole carb is not much harder, and means you can rejet with less crawling around and bending over.

And no joke about the "take it to a pro". I'm friends with a pro on another list, and he is VERY good, and after many years in the business he considers it malpractice to tune jetting without a dyno and a 4 gas analyzer. Otherwise you are guessing. Granted, some people are good guessers, but its still guessing. With the dyno and analyzer, he can dial it right in and spot on in no time flat.

I finally got mine to be "a pretty good guess" and its working well. I still wouldn't mind taking it to a shop with an analyzer and spending $80 to have them verify or tweak it... it would be money well spent. Especially on a two stroke, where proper jetting can turn the bike from mediocre to downright explosive. My kids KX-60 is even touchier... took us forever to dial in the jetting, but now that it's right, that thing is pretty amazing...

So if you enjoy playing with jetting, by all means go for it. I do, and I did. But if you don't, don't feel the least bit bad about paying a pro with pro equipment to just do it for you and get it right.

 

[glad2ride]

Having two different same model carbs sounds like a very good idea to me. Your problem is going to be that in order to have each one set properly for your two different altitudes, you will need to first experiment with one carb at one elevation and get it set properly, then adjust the other one and do a little fine tuning while at that particular elevation.

Do not forget that temperature and humidity changes will effect the jetting, besides altitude.

Start with the pilot jet, then work your way up. The needle for the '86 and '87 KDX200 is an OEM specific needle for the Mikuni carb, and you will have a REAL headache trying to buy standard needles to swap out with the stock needle. You may want to just stick to changing the clip position. The "needle jet" is changeable, but I have never fooled with it. The Keihin carbs that many talk about on here are for 1988 and newer full sized models. Don't get confused, as yours is a Mikuni (or was when stock).

Remember, start with the pilot and work your way up.

Good lcuk with it, and CONGRATULATIONS on having a plated two-stroke in Kalifornia!

 

[sr5bidder]

I would think if you got the jetting dialed in for your 3000-5000ft that another 2000ft up would not be a problem as far as performance.

In my experience when I rode at brown mt. NC (and it was well above 2000ft difference than I normally ride) there was no noticable difference, no fouled plugs..it was great.

sounds a little easier does'nt it?

 

[etard]

Thanks for all the help guys!

My house is at about 2700 ft. Barstow is about 3700 ft. Big Bear goes up to about 6000 ft. and Palm Springs was at about 1700 ft.

sr5bidder,
You're saying that I should be able to tune my bike at home and the variations from 1700- 3700 ft. shouldn't make too much of a difference, all other variables being constant ( temp. hum. etc...)? Now I wonder why it completely sucked at Barstow, but was brilliant in Palm Springs? Should be same humidity, while temp was prolly about 20 F cooler in Palm Springs. I can't tune for that... In the morning it can be 40 F and then by noon it could be over 90F.

 

[sr5bidder]

Thanks for all the help guys!

My house is at about 2700 ft. Barstow is about 3700 ft. Big Bear goes up to about 6000 ft. and Palm Springs was at about 1700 ft.

sr5bidder,
You're saying that I should be able to tune my bike at home and the variations from 1700- 3700 ft. shouldn't make too much of a difference, all other variables being constant ( temp. hum. etc...)? Now I wonder why it completely sucked at Barstow, but was brilliant in Palm Springs? Should be same humidity, while temp was prolly about 20 F cooler in Palm Springs. I can't tune for that... In the morning it can be 40 F and then by noon it could be over 90F.

that my friend is a whole lot of variables you can't even hope to tune for all those changes...try for something in the middle

if your trailering the bike you can set up for the conditions try going down 2 from the palm springs set up on bolth the idle jet and the main when you head up to barstow or just tune it to 3000ft and live with all of it.

20 degres cooler is more dense air = fatter jetting
higher altitude is less oxigen = leaner jetting

all I was saying is that I set it and forget it for my 900-2000ft and when Iget to 1500-3500ft (brown mt.) its still great

I am only swinging 30 degress max in temp throughout the day if that...btw the humidity in your area for sure changes with temp and altitude right ..I have no idea about the left coast other than it must really suck and there must be enough smog that you don't need to premix 2t bikes..sorry just in a bit over my head than I thought I have never lived without humidity

 

[julien_d]

Julien

Earlier in the thread, the man just said he is "not really that patient to swap in and out jets, change clip position and all that jazz" and you are telling him to go experiment with jets. One could laugh at that advise as easy as they could my advise to leave it as is.

If you want to enjoy riding a dirt bike, you're gonna have to learn how to tune it. I apologize for laughing in your general direction, but it genuinely struck me as funny. No offense was intended or implied.

Back on track....


If I regularly rode in places 3,000 feet different, I'd carry some diff main jets for sure. You can get away with the pilot being a little lean or rich, but not the main so much. Luckily the main is super easy to swap out. It's that way for a reason ;). You don't even have to take the bowl off!

You said you found a place where it ran really well how it was jetted. Use that as your base. If you go way down in elevation it will likely develop a lean bog as the air gets more dense. You go up a jet and see what that does. If you go up in elevation and it gets a little blubbery, you can safely go down a jet. Same with massive temp changes. Cold air is denser than hot air, so this adds additional air to the charge leaning things out.

It's a bit of a pain at first, but if you get into a habit of feeling how the bike runs, and taking into account the temp and elevation, it becomes pretty natural. I frequently change needle clip position or main jet size. My pilot hardly ever gets removed, except for a cleaning once in a while. Once you get it close, you'll find the airscrew is really helpful for any non-drastic climate change.

 

[etard]

SR5,
I'm sorry you have never experienced desert riding :nener:

I'm from the east coast, Shenandoah Valley Virginia was my stomping grounds. There were plenty of fire roads to explore, but not really much single track. Well, after I came out here, I soon discovered that The single tracks were bountiful and the trail systems go on forever. From Barstow, my boss and his wife take thier XR650's to Vegas. Then they figured out a way to get to Palm Springs from there, over to Big Bear and then back to Barstow. All on trails, gas line roads and power line roads. It's so much fun out here, it's really a vast oasis for off road vehicles. I Mt. Bike too, and the single tracks and secret trails are growing daily. And the smog isn't bad either, about the same as any large city, I live outside of LA so i don't really see it. Anyway, you should come and visit, hopefully I will have my KDX tuned up by then. :ride:

So I'm just gonna get the skinnier main Jet for Barstow since I am good to go for lower elevation. I might as well get two sizes if they are cheap enough, F it, I'll get some pilot Jets too while I'm there. Oh yeah, did I mention I live about 20 miles from Chaparral Motorsports? That place is a mecca of motorcycle gear.

Well now it's time to man up on this KDX and get hold of the reins. :yell:

Julien,

Thanks for that explanation, I looked at the carb and the main jet is that brass screw in the side by the airbox right? That's cake! If you can get away with just changing that at first, I might get my pilot jet on the consecutive trip. I just don't want to be fiddling with my bike out in Barstow. I'll want to be doing some riding! Maybe if I had a nice enclosed trailer, hmmmmm.

 

[reepicheep]

No, the main jet is at the very bottom of the carb. Turn off the fuel, oosen the hose clamps holding the carb to the boots (both sides of the carb), rotate the carb so the bottom is facing you (from the right side of the bike as you would sit on it), and remove that great big bolt head thing from the very bottom of the carb. You can get to the main up through there. Or just pull the whole bowl off, which is 4 smaller screws, rather then that one big bolt looking thing (which is actually more of a cap).

 

[glad2ride]

Consdier taking off the left side panel and whole airbox. Since it is a 1987 model, that makes it easier than the 1989 and later models.

 

[Dirtdame]

I have an 86 KDX200, also plated. I run a 320 main jet, a 25 pilot jet and the stock needle in the stock needle jet on the 2 clip down from the top. I run my fuel mixed 60 to 1, running an FMF pipe, and run the bike near sea level sometimes and even over 8000 ft elevations, but mostly around 3000-4000 feet. It doesn't seem too finicky running for the most part. Just sayin.... :cool: