Jetting results

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#1
Shortenened version jetting notes for '95 KDX200H1, PWK35 (stock), ram valve, FMF-30 rev, TC-1 spark arrestor, mx2t @ 40:1, FRP torque ring (no jetting significance), 91 octane, Wiseco piston, 2600' elevation, humidity around 30%. Bike likes 42 pilot, Air Screw 1 turn out for most applications, 162 main jet. Any leaner on main makes for hesitation or flat spot on "snap to WOT" (snap to WOT means cruising just off idle and snapping the throttle to Wide Open Throttle). 162 main makes good plug color on 1/2 mile WOT run at max RPM with BEN/4 @86 degrees F. Modifying the Throttle Valve (slide) #5 to approx #6 (cut leading edge up 1 to 1.5 mm---exactly 1.5mm lower than #7 TV) improved mainly 1/8 to 1/4 throttle (leaned it out, not blubbering now) and slightly improved idle to 1/8 throttle(but not enough, still blubbers). A high clip position on needle (like #2) leans out needle straight section and really helps blubbering on BQx, BEx, CEx, and R1174K (stock needle), but introduces a hesitation on snap to WOT. A low clip position (like #5 or maybe #4 on some of the above needles) really reduces the hesitation and hit and makes for a more linear power curve, but increases blubbering on straight section (off idle to around 1/8 throttle). My best needle for over 90 degrees at 2600'(or cooler at higher elevations), 42-162, AS-1, TV#6(modified #5) is BEN/4. It only blubbers to 1/8 throttle, has linear pull on snap to WOT, plug - dark tan, great top end power, some hit when KIPS opens. It starts to have a flat spot on snap to WOT when below 90 degrees. My best needle from upper 70s to 90 degrees at 2600' (or cool high elevations) with same settings is BEN/5. It has more blubbering on straight section, but more linear power - less hit - stronger bottom, has great lower mid range to top end power. Plug - dark tan to light brown. Best all around needle. My best cool weather needle (below 80, or low elevations) same settings, is CCN/3. It has the strongest bottom - most linear power, virtually no hit, slightly less blubbering than BEN/5, strong top - barely softer than BEN/5 (power barely less crisp mid to top than BEN/5. Plug - dark tan to brown, sometimes darker if riding around at 1/8 throttle. Can feel richness when chopping throttle through bumps or landing from jumps. Backing AS out to 1.5 brings back a flat spot. C needles seem to be more sensitive to AS adjustment than B needles. Needles tested: R1174K/1/4/5, CEL/2/4/5, BGQ/5, DCQ/2/4, CEP/4/5, CCN/2/3/4, BEN/4/5, BEQ/5. Pilot jets tested: 38, 42, 45, 48. Main jets tested: 155, 160, 162. Throttle valves tested: #5, #6 (#5 modified to approx. #6), #7(which was so lean it tried to idle near red line - even with my richest possible jetting). My #7 TV doesn't have the cut out relieved area around the bottom of it like my stock slide does. It just has filled in tapered area all the way to the bottom edge. BTW, This is my 1st internet post of any kind.
 

G. Gearloose

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#2
Originally posted by Rhodester
A high clip position on needle (like #2) leans out needle straight section and really helps blubbering on BQx, BEx, CEx, and R1174K (stock needle),
Welcome Rhodestar.

Sounds like you are off to a good start. Very ambitious

However, clip position does not lean out a straight section. Needle Diameter, Air screw, pilot and TV cutaway affect mixture in the region where the straight section applies.

I also don't comprehend the 'good color after a WOT' observation. Search and read up on reading plugs after WOT 'plug chop' (chop has two meanings, both apply...) ;)

Set your main for WOT only. Switching to a different main to 'fix' the wick-open response is counterproductive, and complicating the diagnosis.
 
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#3
G. Gearloose, thanks for your input. Maybe you could suggest a remedy for my hesitation/flat spot situation that can effect it w/o the main jet figuring into the equation. I only went 1 size richer on the main to have a good result dealing with the hesitation. For some reason my bike seems to like a richer main than many others on this site seem to be using. I can definately notice a decrease in blubbering below 1/8 throttle with more staight section on the xEx and xGx needles being lower in relation to clip position. Do you think I may have some other problem effecting my jetting? I have done WOT chop tests before, but I must admit that I am mainly using seat of the pants feel and experience to set up my main jet. For example, a 155 main on my bike has a certain "raw" sound and reduced power output at WOT/max RPM. With a 160 or 162 I have no 4-stroking, great power, and minimal smoke or spooge. I'm definately still in the learning process and very much appreciative of your input. I've even considered purchasing a torque pipe (-35) to try a different approach to the hesitation/flat spot problem that I've been trying to work out through proper jetting. All this testing has taken more than 3 months. I wish I could figure out a way to completely eliminate the off idle rich blubbering up to 1/8 throttle too and still have no hesitation on my snap to WOT test runs. Right now I'm just living with it as the lesser of two evils.
 
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#4
continued....I have tried needles as lean as I could go on the straight section, such as BGQ, DCQ, and BEQ. Sudco was out of CEQ so I tested with CEP. I still had some blubbering below 1/8 throttle with only a slight reduction over the BEN, and CCN needles. The bad part is that I increased my hesitation/flat spot problem with the leaner straight sections on these needles. So I went back to the xxN diameter to eliminate the hesitation. I failed to mention in my bike information that I also have removed my air box cover.
 

G. Gearloose

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#5
Hang tight..
I'm short on time right now to really digest your work to date..but if your fortunate CC and others may find you problem challenging and you'll be in good hands. There's a lot to digest there so in a day or two your issue will get exposure.

Remember you have to run a big pilot to get a large dia needle to work ok. Many of us have opted for smaller dia needles, matched to the TV cutaway, with smaller pilots.

Also..have you verified KIPS and reeds are in order?
 

acutemp

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#6
Rhodester,

Excellent first post, it's always good to see people dive in and look to really understand how different setups can change "personality" of their bike's power delivery. Thank's for sharing your finding's as post's such as this are very helpful to other's that are trying to achive the same goal of fine tuning the jetting on their KDX's.
Your #7 slide sound's like a pre-95 non air striker style slide and it won't work in your 95's carb. :ugg: I do prefer a leaner slide than the stock #5 though and the #6 that you have is a step in the right direction and is what I would work with.
I wouldn't worry to much about needing a bigger main than most run, every bike is different and running a 162 main is not unheard of. If you have room to run wide open for a half a mile then I would jet on the side of safety. The carb body can tend to wear over time also which can cause the need for a bit richer jetting on some bikes.
My thought's would be that the richness at 1/8 throttle that you are running into is due to having your jetting package a bit off. It sounds like a little tweaking with the crossover points of the different jetting circuit's might be needed. While going leaner on the straight section to try and clean this up you found that you needed to go to an extreme clip position to compensate when wicking open the throttle. This get's you into the taper quicker which helps when opening the throttle quickly but is to rich otherwise. Here is what I would give a try if you are up for more testing, CEL#3,4, #6 slide, 40-42 pilot, 160 main. It is a setup that is leaner in the area that you are trying to clean up. When changing from a B taper to a C taper you can usually go 1 step smaller on the main.

If you have access to an Excel spreadsheet program I would highly recommend getting a copy of JD's jetting guide as it will allow you to input all of this data and map your jetting curves on a graph. This is especially helpful when working with multiple slides and needles. :thumb:

Good luck it sounds like you are on the right track and with a bit more fine tuning you should have it dialed in.--Dan
 
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#7
I just got done doing the jetting dance with Gatorkdx on his 1990 200 and it took a couple of weekends to get things right. In retrospect, probably should have started were we ended by cleaning the air filter and silencer thoroughly before attempting to rejet. I didn't notice if you have removed the airbox cover?? How long have you run the new pipe with improper jetting?? When I removed the PC silencer it appeared ok---until I cut the tape and unrolled the packing. The rear half was completely saturated with spooge and even somewhat hardened and stuck to the baffle requiring that it be scraped off with a wire brush. Our tuning efforts ran into trouble at about the same spot yours did---lack of smooth transition off the bottom end. After allowing the bike to breath a little better--BINGO!! Hope this helps. --Jay
 

canyncarvr

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#8
Dan said: 'It sounds like a little tweaking with the crossover points of the different jetting circuit's might be needed.'

Something to consider (read, 'incredibly important!') regarding needle choice and crossover points.

The L1 designationof a needle is not the length of the straight section!! It is the length to the point at which the diameter of the needle is 2.515mm. That is generally called the 'magic' number. It's 'magic' cuz who knows why that diameter was chosen anyway.

I digress.........

This magic number business gets critical when changing tapers.

Consider the following: With a 'slower' taper of 1'15" (1.25º/'B' taper), the taper has to start earlier (higher) on the needle to get to the magic number compared to a 'faster' tapered 1'34" (1.5º/'C' taper). Everything else staying the same, that will make the actual straight section (the part with no taper whatsoever) of the 'B' series needle shorter than that of a 'C' needle.

Compare a DEK-3 to a CEK-3 on JD's spreadsheet and you'll see that taper start showing up with the CEK being considerably richer at 1/8 throttle.

Which is something for you to consider....a 'D' series needle, but not one with such a large diameter as the 'DCQ' (2.745mm straight). A smaller diameter combined with a later starting slope (longer L1) will give you a clean (no plug loading) bottom and a smoother transition point...maybe a DEK.

Information on JD's spreadsheet can be found here.

****EDIT***
Well, sorta. Looks like he changed horses again. He's back at thumpertalk, it seems. Info can be had above, but the 'buy it' link is dead. I've asked him for verification, but it looks like THIS will work. I'll update this (again) if I find out different.

Cheers!
****edit****

Your spent time will be well worth it. Congrats on the effort! ;)
 
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#9
Guys, Thanks for your additional input. I own 2 businesses over here in the Boise area that are on the grow so I'm a little short on bike experimentation time. In response to some of your input I'll share some further info. I recently cleaned my silencer with my torch, wire brushed it, and repacked. I am aware of the different taper beginning points in relation to the L1 measurement on the different needles I have been testing with (Bxx, Cxx, Dxx) thanks to your very informative posts from the past. I purchased my KDX around July 1st this year and it already had the -30 pipe (the older "fatty" designation). Unfortunately I don't have Excel on my computer...I wonder if JD's charts can be obtained through other means? CC, I'm giving considerable thought about trying some more D tapers to follow your suggested course. Acutemp, I think you may have really hit a bingo when you suggested that my slide is pre-air striker. I had heard that there was a difference but didn't know what it was. That may solve a lot of my problem right there if you think the right #7 slide will significantly effect the idle to 1/8 throttle blubbering situation that I have. If that will lean it out in that area I can probably run some richer diameter needles and get the results I'm looking for. What do you think? I did some testing with the CEL needle in clip positions 2,3,4,and 5. I used a 38 pilot trying to compensate for the richness of the straight section. I was using #5 slide at the time and tested the needle with a 155 main (CEL/3,4) and a 160 main (CEL2,4,5) at 75 to 80 degrees. CEL/2,3 had hesitations, the rich main jet turned the hesitations into just flat spots which were never really eliminated even in the /4 and /5 positions. Of course, there was lots of blubbering on the straight section. Perhaps I can try this again with the air-striker #7 slide. Thanks again for your continuing help.