Specific to KDX?

[Bizerk]

Ok, before you read this I have to say that I have read all the posts on carb tuning etc and find myself pretty knowledgeable but certainly do not know everything...that's why I'm here.

Here it goes...bike sputters/crackles off idle when you open the throttle then runs great the rest of the time. I know it's running rich. I did the pull ht echoke a little up and it does not improve it. I am down to a 40 pilot. Had a 45, then 42 and now 40. There isn't much lower than this that you can get. I am running a 155 main, 1173k needle, played with the airscrew thing, totally cleaned the heck out of the air filter, air box and carb. Running FMF Gnarly pipe, Boyesen reeds(new) happened with old too. Bike runs absolutely mint all other times-what a blast, just can't stand the crackle-not bog. runing rich.

So my question is I want to try the stock needle 1174 instead of the 1173. After reading about needles etc on the KDX site this wil lean the mix a little and does effect from idle on up.

What do you guys think?
Sorry about the book.
Thanks in advance.

 

[canyncarvr]

Great...a stroke of a key and the whole thing is history.

OK..here's the short version.

I understand you are talking about a 4-stroking situation. I don't know about the 'crackle' part..........

If it's 4-stroking that's happening, you're too rich on the bottom.

A -74x is headed the right direction but probably won't cure it.

What does 'gnarly' mean? Nothing in regard to pipe profile. The torque and rev profiles jet differently (rev requires richer). Even so, if it's a rev you have (richer required) a 155 is possibly not correct and it can and will effect all carb circuits including idle.

Don't know about '..isn't much lower..' but a 38 pilot isn't at all unreasonable if that's what is called for.

Consider a 'C' or 'D' needle. A sharper º taper will keep the 'straight' section of the needle in play longer.

You realize that the 'straight' part of the needle is not actually straight? That's a big deal. The most critical part of understanding needles (sez me). L1 refers to the length of the needle TO a diameter of 2.515mm. So, L1 indeed includes part of the taper of the needle. The sharper the angle of the needle taper, the later the taper starts.

Make sense?

 

[Bizerk]

Thanks canyon.
Pipe is actually marked as a FMF "Burly" yes "Burly" pipe. I believe it was an original version of the Gnarly Torque not sure.
I'll try to make this short and to the point but I need to understand what you're suggesting. I for the most part under stand what you are talking about but...

About the needle. Definately makes sense about the taper and keeping the main diameter in the main jet longet will keep it leaner at lower throttle opening.
* I went to MX south to look at conversions from the OEM numbers to what they list.
* Please clarify something- currently I have a R1173K needle,
and you are suggesting to try a sharper taper of a C or D. What is confusing to me is this. Are you talking about a 1174C? OR are you refering to the conversion thing whereas C=13, meaning that the number would read 1374K?

* 2nd and third are the taper angle
* 4th and 5th are the diameter
* last is the L1
* so...with the needle I have now is: 11=taper angle, 73 diameter and K=L1.

so last but not least ...if you look at MX Souths jet needle conversion table...would I go for a C Taper; Q Diameter; G L1 ?

Help Canyon...were almost done...I think.

Thanks Bud!
:thumb: :worship: :worship:

 

[canyncarvr]

Yes. FmF did use the name 'Burly' for awhile. They got in trouble from someone else that was already using the name. Then they went to 'Gnarly'...and a few other names scattered around.

Still, it's important to know what profile you have. Usually there is an identifying stamp on one of the hanger tabs that will have either a -30 or -35 (and some other letters). The -30 is a rev profile, the -35 is a torque profile.

Also, note that the rev is much bigger physically than the torque. Something around 14" compared to 11" when measured at the largest part of the bell...where the two cones (con- and di-verging) meet.

The only point of bringing this up is to advise caution when someone tells you to jet like 'this'. It doesn't work that way. YOUR bike has to be jetted to run the way YOU want it to. Taking someone else's idea of what works doesn't (work, that is). Which pipe you have would have a lot to do with that.


re: '* Please clarify something- currently I have a R1173K needle,'

Take a look at CDaves needle decoder on his site (linked in the 'every kdx rider should read..' thread stickied to the top of this forum).

The 'K' part of that kawi number is L1, the '11' part is the taper angle.

So, no.......I'm not referring to an R1174C. Yes, I AM referring to a 'C' converting to a '13'.

re: '...with the needle I have now is: 11=taper angle, 73 diameter and K=L1'

Yes.

You won't find (well, to tell the truth, I haven't looked but doubt you would find) an R1374K. Keihin numbers are of the 'CEK' pattern where 'C' is the º. 'E' is L1 and 'K' is the diameter. So, the needle you mention above would be 'CGQ'.

KDX riders with oem throttle valves (slides with a stock 5mm cutaway...on 'H' model bikes anyway) have reported good results from CEL needles. A 6 or 7mm cut slide will help, too...but more along the line of a CEK needle with that slide.

You can get your slide recut, or just buy a spare with a different cut. Ron (RB-Designs) can help you with either of those choices. When I tried to buy a #6 from a local dealer, it was several weeks and two wrong slides before I asked Ron for one. A couple days later it was in my hand.

BTW...the straight section of the needle isn't going to be in the main jet. It will be in the needle jet (not to be confused with the needle itself). The needle jet isn't usually messed with.

The main jet will effect off idle and idle. Try it yourself if you wish. Get your bike jetted correctly, then try putting in some bogus main and see what happens. While the metering device in lower throttle ranges isn't the main jet, the main jet orifice isn't plugged off in those lower throttle ranges.

re: 'Bike runs awesome except off idle'
Likely an airscrew adjustment problem. Hi idle is not likely the best setting. It's a place to start. Set it to best throttle response under load in a relatively high gear (say 2nd gear from a slow walking speed...with a quick flick to about 1/2 throttle).

re: ' Bike runs awesome except off idle (putting around)'

If that's a 4-stroking symptom from plug loading (you didn't mention anything about that) you are referring to, that is a common kdx problem due to a less than stellar needle choice.

I have been using a DEK needle. I can run at idle speeds on any length downhill. At the bottom there is zero plug load-up. There is instant throttle response with zero burble/blubber/goober (4-stroking).

I'm not saying you should use a DEK needle. Just that a 'no plug load' situation is certainly attainable. I am using an '8' heat range plug (BR8EG).

Keep after it until you're happy with the result. What you learn in the process will hold you in good stead for the rest of your riding days....and a good number of other people you ride with that don't 'bother' with jetting cuz it's too much trouble.

They are missing out on a LOT of what their bike has to offer.

Good luck!

 

[Bizerk]

Awesome advice Can!!

I will look at my pipe markings late to see if it is a torque or rev pipe.-Thanks.

I totally understand about the needle jet/jet needle thing too...not sure why I put main jet..must have been tired last night.

I have played around with the airscrew with not much luck-more than two turns out now and still is girgling just off idle if you hold it there, otherwise if I jolt it to 1/2 throttle she'll go like a raped ape!

All I got to do now is figure out the correct needle to try!!

Thanks for all of your great advice! :thumb:
:worship:

 

[canyncarvr]

You're certainly welcome.

Adjusting the airscrew isn't going to effect a too rich bottom that comes from the needle.

Rule of thumb is more'n two turns out and it's time to consider a leaner pilot.

Give the 38 a try. A too lean pilot will showup commonly as a high idle on a choke cold start. I mean real high...like you'll be wanting to hit the kill switch to limit the revs.

That still won't resolve the oem needle problems.

BTW, you can get a finger adjustable idle screw from Ron @ RB-Designs, too. It's not so much a big deal on the oem carbs, but Ron's modified carbs have a very useable (meaning it actually does something) pilot circuit and small adjustments make a big difference, so doing it with your fingers makes it a snap.

re: and still is girgling just off idle if you hold it there

THAT may well be a different issue. 4-stroking under demand due to plug loading (again that term) isn't a good thing. A happy 2-smoke under no load will 4-stroke at most throttle positions if you 'hold it there'. They key here is no load.

Make sure you're chasing the right thing.

On level ground in 2/3 gear @ 10-15mph, throttle held steady your bike will be 4-stroking. But throttle response should be right there, right now.

 

[Bizerk]

Thanks again....

By the way...I'm using a BR8EIX plug.

One thing I haven't tried is to drop the needle one clip to lean it out a little. I'm at the 3rd clip from the top right now with the 1173K needle. I could put the clip at 2nd down from the top and try that before I start going out buying all sorts of needles. What's your opinion?

Is there a rule of thumb as far as clip position to start on with any new needle? Like in the middle?

Throttle response seems good most of the time as I mentioned before just the "sputtering" at off idle and especially when she's cold.

Thanks in advance.

 

[shr]

So try dropping it and see what happens, it's one of the easiest things to try. If it's better your going the right way, if it's worse then..... well you know.

I think you have answered your own question; Yes experiment and find out what works for you. Do the fine tuning; jets, needles and clip positions. You already know that the engine operating temp. should be a well warmed up engine! So why try and tune for a cold engine?

Don't forget about the mixture screw, it can help too.

 

[Junkyard Dog]

Sounds normal to me for being just off idle, I run the same setup as your's (03 200) except I run a 45 pilot and a br8(eg) plug. It chugs when it's cold and just off idle too until it warms up then were smiling. That's a 2 stroke for ya. You can mix 3 different gallons of gas, say 1 at 50:1, 40:1 and 32:1 If your trying to lean it out start with 32:1. When you find the one the bike likes and yer happy with use that, it saves time and a few bucks on changing jets.

Use the left over gas for your lawnmower, so what if it smokes a little, just tell the neigbhors it's foggy out.

 

[Bizerk]

Thank you guys! I appreciate all the support. :thumb:

 

[Buckholz]

Check your float height..... sound like fuel level a tad high....

 

[Rhodester]

Bizerk, I tried 9 different needles, 7 different mains, 3 different slide cuts, and 5 different pilots to cure just the problem you're talking about. I found that regardless of the needle I was using (to a degree) it would 4-stroke just off idle when using clip positions low on the needle and would clean up when using the higher clip positions (but that created some other problems for me...that's another story...). Ultimately I had the best results at cleaning it up just off idle when I conferred with Eric Gorr who suggested that I advance the timing slightly ahead of the most advanced timing mark. I also just got my cylinder and head back from him to add some compression and trim the cylinder base slightly to focus a little more power toward the bottom end. I haven't had time yet to put my bike back together and test ride it yet, but I know that advancing the timing had the best results at cleaning up that just off idle 4-stroking. Apparently, these engines don't run much compression (7.9:1) and that hurts efficiency of the combustion process at low RPM's in particular, especially at higher elevations. Advancing the timing adds a little bit of pressure (compression) to the combustion process.

 

[Bizerk]

So, two questions. What were the other issues that happened by raising the clip needle? You said that cleared up your low end problem but created other issues that you did not comment on. Second, won't advancing the timing cause other issues like no top end or I'm a thinking about this wrong?

Thanks.

 

[Bizerk]

I guess I answered one of my questions. I got this from Eric Gorr's site:

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.

 

[Rhodester]

Bizerk, Eric told me that "these engines make so little pressure" to begin with that advancing the timing will have little effect on the revability of the engine. He was right. I couldn't see any difference in the ability to rev out as good as it did before. I was also concerned that engine temp might become an issue. So far no problem there either, and I purposely rode in a way to cause the engine temp to be high.

Concerning the "other problems" issues. For some reason my bike tends to have a hesitation or (at best) a flat spot when snapping the throttle open to WOT when riding at low RPMs under a load. The only way I've been able to minimize this problem is to go way rich on the main jet while keeping my needles in clip position 4 or (mostly) position 5. The problem exists over a wide range of differing needles. In addition to just having to run rich, as soon as I raise whatever needle I'm running (lower the clip to 4 or usually 5) it turns blubbery rich just off idle...even when experimenting with a much leaner main jet. When trying to compensate with a leaner slide cut (#7) it makes it nice and crisp above 1/8 throttle, but still blubbery rich from just off idle to 1/8 throttle. I've been fighting this problem to no avail since I bought the bike (used) 9 months ago. The base trimming and compression boost is my latest attempt at solving it. The only thing left for me to do after that is to buy an RB Designs Air Striker and see if that cures it. I'm currently assembling my bike and may have it together in time tomorrow to try my latest batch of modifications out.

 

[Bizerk]

Thanks for the info,
With my current setup it is great, snappy powerful and no hesitations from 1/8-1/4 to WOT. Its just the nagging burbling when you open the throttle from off idel to about 1/4 and she sure is a cold blooded beast. The bike idles fine, its again just the off idle to 1/8 or so. I might check, change the timing to see what happens but first I am going to drop the needle one clip to see what happens. I wasn't able to get out to do that or ride today (yardwork around my house) but will try hopefully tommorow.

CHeers..

 

[Rhodester]

Well, got my bike back together this afternoon. I only had a chance to ride it around my neighborhood for some initial jetting tests. Eric only raised the compression 8 LBS (from 134 lbs. to 142lbs.). Could be that he was concerned that I wanted to be able to run 91 octane pump gas so he didn't raise it any more than that. I haven't had a chance to open it up, but everything below about 6000 RPMs appears to be a little cleaner running. I've settled on 42,CEL/5,155,AS 1 1/4 for now (low 60s outside temp. 2600' elevation). It still will rarely hiccup or hesitate when wicking it to WOT, but most of the time it has nice and linear pull if it's nice and warmed up. I still, however, have my same problem (only slightly less) of being blubbery rich from just off idle to about 1/8 throttle. If I go to CEP/5 it is very clean between idle and 1/8 throttle, but then I'm back to a big hesitation when I wick it. CEL/4, 155 and CEL/4, 160 also gets me a big hesitation, but is a little cleaner off idle to 1/8 throttle, but not as clean as CEP/5. I also tested this afternoon with BEN/5, 160 (had a flat spot with a hiccup) and R1173N/5, 160 (had a pronounced hesitation). So, I guess I'll have to save up some coin for an RB Designs Air Striker and hope that that $320 will finally solve my problem (after 9 months of experimenting with every fix imaginable and many hundreds of $$$).

.....and yes, my RAD valve reeds are tight and it passes a leakdown test with flying colors. I'm currently running a -35 FMF with a 'Q' silencer and no air box lid. Carb is stock with #7 slide. Timing is advanced just past the most advanced line (as per Eric G.). KIPS was cleaned as part of this latest project (by yours truly) and my wiseco piston and rings were cleaned and reused because they are still within spec.....I'm still open to suggestions if anyone has any.

 

[m0rie]

Carb is stock with #7 slide.

The 95+ KDX's came with #5 slides and the 89-94's with a #6. Thats one of the mods that ron does with the RB-Carb mod, he recuts the slide to be a #7.

-Maurice

 

[Rhodester]

mOrie, sorry, I didn't communicate that well. I mean I have a stock carb, but I've trimmed my slide to #7, which is what is in it now.

I was awake in bed last night thinking about lengthening my L1 with a Dxx needle to get the leaning effect below 1/8 throttle I've experienced with Cxx and Bxx needles in high clip positions. The only Dxx needle I've tested with is a DCQ, which may be way to lean of an L1 diameter (although that's the stock diameter). There may just be something to the Dxx needle thing that CC keeps talking about. There just might be a a DEK,DEL, and DEM in my testing future. I know, I know....I'm a little slow, but eventually I get there.

CC, if you're reading this, what clip position (and total jetting figures for that matter) are you currently using? What's your riding elevation and general riding temp?

 

[m0rie]

Ah, that makes more sense :) Any chance you might have miss cut the slide? Is the slide grooved at all? I think your on the right track looking at the D series needles. CC should be able to run a few needles thru the JD spreadsheet and give you a couple ideas to try.

-Maurice

 

[Rhodester]

If anything the slide is trimmed just slightly shy of #7. The slide looks like it has very little wear. I talked to Ron (of RB Designs) about that issue. Last time I was in Portland I dropped by his shop. He was most gracious to give me a few minutes of his time.