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JD Jetting kit woes


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Got a JD jetting kit and I also rebuilt the top end on my bike, need some advice.

2005 yz250

3000-4000ft

65+F (20 Celcius)

Stock engine with stock pipe and shorty silencer

Twin air filter

Started right away with the lean needle on the middle clip position with 170 main and 45 pilot.

Bike was fully warmed up and went for a ride and noticed that the top end was bogging along with the mid, bike ran like crap couldn't do any climbing or technical stuff.

Raised the clip position to the top and tried again, sputtering was gone from top end but still apparent mid throttle. bike ran much better but mid throttle was lacking.

Popped in a 168 and had a bit better top end but mid is still crappy.

Should I keep on going leaner here with the main?

How come I need to run the leanest clip position with the lean needle to get decent performance? Also there is still some bog when cracking the throttle open, I adjust the air screw before I ride every time and can get ok throttle response but there's always a bog.

Thanks for your help

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One thing I found interesting with the kit was the needle and how dramatic clip positions determine engine performance.With the stock needle N3EJ I found that changing the clip position made no difference what-so-ever! I could have it leaned out, or rich as hell and not really notice a difference at all... Then again I didn't really play with it more than once.

I emailed him and we'll see what he says, I post any new info I get.

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James has replied to my email, here is what he had to say

Brent,

A bog on a 2-stroke motor is usually from lean jetting, not rich jetting. How can you be sure that you are not running too lean?

(sorry, but I have to ask... Is the air filter clean? ..and what brand of air filter? ..and are you using filter skins?)

What oil brand and premix ratio are you using?

The Red marked needle should be in the range between the #2 , #3, or #4 from top clip positions.

The Blue needle will usually be in the #3 or #2 from top clip positions.

Red #1 will normally mean something else is wrong, like a leaking crank seal letting transmission oil into the lower cases. This would make the bike run with extra smoke, regardless of lean jetting and bogging.

Let me know how the bike runs with Blue #2 and Red #4 with a #165 main jet.

Thanks,

James

I am gonna try what he said on the weekend when I go out to the creek and reply back with my results.

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A bog on a 2-stroke motor is usually from lean jetting, not rich jetting.

this makes no sense to me....i got the same issue now with my 200, jd jet kit but it bogs when im doing a technical rock section from a dead stop, i have to rev the crap out of it to keep it from dying. im going to go from a 42 idle to the 38 they provided and test it.

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One thing that seems totally F*d is the fact that the stock needle ran pretty good with no issues in the mid-high end RPM. When I put the lean needle in on the middle clip position right away I was having bog/gurgle in the mid and especially high, like it wasn't fully clearing it's throat or wasn't fully warmed up even though I went on a 30 minute ride... You would think that if the stock needle was rich and the red needle was lean that I would be running even better with the middle clip position. It was only until I hit the leanest clip setting that it cleared up all the issues mostly. Maybe the red and blue marked needles got marked incorrectly at the factory??? 🙂

I put in the blue needle as he suggested in the second position from the top, I have yet to try it out but I'm going to give it a small go tomorrow and a big go on sat/sun.

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Same problem here, 03cr250 Started on red needle,3rd clip bike had huge Mid throttle blubbering and hesitation,2nd clip was an improvement, but still wouldn't clean out,1st clip now is much better with only slight mid bog every few laps,almost perfect,almost...

I'm going to test with the blue needle next week just to verify.

I have no smoke, plug is good, a little light, but I will go back up one on the main to make up for slight lean condition on top.

Filter is clean twin air-no skins

New intake boot,reeds,gaskets

94deg

C12

390main

32.5pilot

As 1 1/2out

S4 nozzle

Will post up if I get it perfect, but I can't see how the richer blue needle could help if red positions 3,2,1 progressively cleaned up the jetting,also since red 1 is still not totally hesitation free? I do want to mention James has been more than helpful, even sending a part at his own expense, excellent support.

Edited by pieplatesnductape
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Here is some more follow up from jay at jd jetting

My second inquiry, I still have not tried his advice just a couple of other questions;

James

Thank you for taking the time to help me out,

My air filter is clean, it is a twin air filter and I use maxima FFT (blue tacky stuff) on it. I use Yamalube and sometimes Castrol 2 stroke oil in my gas, I run 92 (no ethanol) octane with exactly 30:1 premix ratio (this is what the 2005 service manual specifies). Currently right now I am using Yamalube in my tank, the gas is only a week old.

Upon start-up the bike does smoke quite a bit, especially when you blip or open the throttle and immediately after the throttle slide closes plumbing blue smoke comes out of the pipe. After the bike is fully warmed up however, this is not nearly as apparent but still there.

Before I try your advice (165 with different needles/positions) is it possible that the maxima FFT blue filter oil is just too constrictive? Should I try regular motor oil?

Brent

He replied here with;

Brent,

Have you tried running the premix at 40:1 or 45:1, as most riders do with your bike?

I think you will find the bike will smoke less and allow richer jetting that doesn’t bog with a ratio close to this range.

If you try running less premix oil, use a #170 main jet and Red #3 as an estimate to start with. Adjust the idle mixture with the air screw for good response from idle, that is only slightly smokey when the motor is fully hot and has cleared out after running thru the gears a few times.

I don’t think the filter oil is an issue with the Twin Air filter.

Thanks,

James

Going to try the bike out today, see what happens here.

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Well I tried the rich needle second clip down with the 165 today and it ran awesome. Full poewr throughout 1/8-full throttle, no stuttering.

Doesn't make sense, but it worked... nuff said.

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we should be able to verify rich or lean needles with a mic shouldn't we?

Yes, you should

IIRC the JD blue and red are similar in the taper but the main difference is the straight section diameter. When you test the needles you shouldn't go through the same needle 3-2-1, you need to alternate between red 3, blue 3, red 2, blue 2, etc.

Also, BOG in the low throttle region is generally a sign of a 2 stroke being lean. A blubber, gurgle or sputtering is generally a sign of it being too rich. IIRC the JD blue and red are similar in the taper but the main difference is the straight section diameter.

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The bog at 0-1/8th throttle is still there with the blue or the red, I'm pretty sure it's a small oil or air leak.

One of my bikes was lean bigtime on the main, and when you opened up the throttle it sputtered and gurgled it did not bog, so I would have to say that the opposite of what you say is true. Not trying to start anything this is just what I have observed.

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That's why I like to use the word generally and usually point towards low throttle openings. A main jet issue can represent itself in different ways as can a pilot or clip issue. Low throttle lean bog is usually easier to identify and a much more common of an issue than a grossly incorrect main jet.

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Rain today, so I did a quick inspection of my needles to verify. I used a micrometer on the jd red,blue, and finally the stock needle 38-73 , keep in mind my bike is a 2003cr250, not a yz, but it's the same general idea. I measured all 3 needles at 4 equal positions along the needles. I found the red needle is marked correctly, as it is very slightly larger (thus leaner)in size than the blue, usually around .001 larger to be exact. I did find it surprising that the stock needle straight section was the largest of all, making the stock needle the leanest at 0-1/8throttle. Then the stock needle gradually becomes increasingly richer (compared to both jd needles )from 1/4 to 3/4 throttle.,and gets drastically richer(again by comparison) than both jd needles near 3/4 throttle.

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