Jet kits vs. OEM jets

[Mark6299]

I will try to do some jetting soon and would like to know about different jets. It looks like some people use JD Jet kits. I know they have a tripple taper but are they worth the money? Why should I buy a jet kit over buying a few OEM jets?

[The Spanky]

The main jet and pilot jet in JD's kits are just OEM jets. His needles however are a proprietary design. He has his own theories on needle design, and they seem to work well. I actually just ordered his needles for my KX 250, because I've not found an OEM needle yet that completely satisfies me. Every OEM needle I've tried makes the bike either too rich from 0-1/2 throttle or too lean from 1/2 to 3/4 throttle. I can make the bike happy in on or the other spot, but not both at the same time. I talked to him and he claims his needles will solve that dilema for me. We'll see.

Basically, JD has done all the jetting research for you, and gives you the best range of jets for your bike with literature to tell you when to use which one. You're paying for his research, so you don't have to do the trial-and-error testing yourself.

[Willwater]

Basically, JD has done all the jetting research for you, and gives you the best range of jets for your bike with literature to tell you when to use which one. You're paying for his research, so you don't have to do the trial-and-error testing yourself.

Maybe it is only the case for YZ250's but when I got my kit from JD it was far from no trial and error. It came with two needles and instruction that say to try red one in the middle position and go from there. Pretty much the same thing I could have done using 7 dollar factory needles. No altitude vs temp charts or anything like that. It did come with a nice case to keep all my other needles and jets in so that is a bonus.

[The Spanky]

Maybe it is only the case for YZ250's but when I got my kit from JD it was far from no trial and error. It came with two needles and instruction that say to try red one in the middle position and go from there. Pretty much the same thing I could have done using 7 dollar factory needles. No altitude vs temp charts or anything like that. It did come with a nice case to keep all my other needles and jets in so that is a bonus.

Well of course you'll still have to do a bit of testing on your own to determine the best clip position for the conditions. But by "no trial and error" I mean that you don't have to guy buy a handful of needles and test them all to find the best one. Been there, done that.

I'll let you know if mine come with any literature, I was under the impression that they would?

[Stephan26]

FYI, thought i'd chip in...my kit (drz400sm) came with all the hardware and specific setup instruction on which needle, clip position to use for my altitude/bike setup...plus the bonus plastic case to store my other needles...!

[highmarker]

does your kx have a power jet?

[The Spanky]

does your kx have a power jet?

Yes. But as far as I know, there are no richer orifices available for it, only leaner. I could be wrong.

[Willwater]

I guess, I just expected more than I got for 70 dollars. If I am paying 10 times the going rate for a needle because of research I guess I expected a jetting chart. I emailed JD trying to get just one needle because I really did not need all the jets which I already had. His response was that he would not split the kit up because I was really paying for the research. The needle did work well for my bike, but honestly I think a leaner slide makes a much bigger difference. Especially for the condition you are describing where you can't get the bottom lean enough without leaning the top out too much. I agree that finding that perfect needle is a pain in the arse and if the JD needle fixes that than I guess it is worth it for most people.

[hallsy]

The main jet and pilot jet in JD's kits are just OEM jets. His needles however are a proprietary design. He has his own theories on needle design, and they seem to work well. I actually just ordered his needles for my KX 250, because I've not found an OEM needle yet that completely satisfies me. Every OEM needle I've tried makes the bike either too rich from 0-1/2 throttle or too lean from 1/2 to 3/4 throttle. I can make the bike happy in on or the other spot, but not both at the same time. I talked to him and he claims his needles will solve that dilema for me. We'll see.

Which of the O.E.M. needles did you try?

Yes. But as far as I know, there are no richer orifices available for it, only leaner. I could be wrong.

The powerjet in your carb is the same as the leak jet in the 4t FCR carb (N424-52-xxx). Looks to be available in sizes from 35 to 140. http://www.sudco.com/CatalogJPG/061.jpg

[jayc250x]

Why should I buy a jet kit over buying a few OEM jets?

Whew - now THAT's a good question.

JayC

[The Spanky]

Which of the O.E.M. needles did you try?

NAFF (stock), NAFD, NAFE, NAFG, NAFH, and the Team Green recommended N3WE, which was the best of the ones I tried. But it still leaves the bike slightly rich from about 1/2 to 3/4 throttle if I set the clip where it runs cleanly below 1/2 throttle.

The powerjet in your carb is the same as the leak jet in the 4t FCR carb (N424-52-xxx). Looks to be available in sizes from 35 to 140. http://www.sudco.com/CatalogJPG/061.jpg

I did not know that, interesting. It never occurred to me that any FCR parts could cross over. If the JD needles don't fix the issue, I'll have to investigate that further. But doesn't the powerjet only operate from 3/4 to full throttle, and only below about 8000 rpm?

[highmarker]

power jet works on a 2 d map, rpm and tps. if the rpm is low and the throttle is farther open there is assumed to be more load on the motor. So the rpm it shuts off the fuel occurs later. and visa versa,

you can't change the map but you manipulate a little with tps setting and jet size.

have you looked at PC's jetting recommendations? sometime they are a good resource, but working with James and his needle should get you dialed in.

[hallsy]

NAFF (stock), NAFD, NAFE, NAFG, NAFH, and the Team Green recommended N3WE, which was the best of the ones I tried. But it still leaves the bike slightly rich from about 1/2 to 3/4 throttle if I set the clip where it runs cleanly below 1/2 throttle.

Thanks I was wondering which needle you preferred. I suspect you know the NAF_ needles differ only in a small area from closed to @ 1/8 throttle. Did you know the N3WE is essentially the same as your NAFE, except that the taper is moved so that it runs 1.5 clip positions leaner? N3WE in clip 3 is the same as NAFE in clip 1.5. If you could move your N3WE needle a 1/2 clip leaner would it clean up 1/2 to 3/4 throttle?

I did not know that, interesting. It never occurred to me that any FCR parts could cross over. If the JD needles don't fix the issue, I'll have to investigate that further. But doesn't the powerjet only operate from 3/4 to full throttle, and only below about 8000 rpm?

The FCR actually uses the same main and pilot jets too. My YZ manual indicates the powerjet delivers fuel from 1/2 to wide open throttle, below 8,500 rpm. I would guess the rpm at which the powerjet closes may vary from one OEM to the next.

[The Spanky]

Thanks I was wondering which needle you preferred. I suspect you know the NAF_ needles differ only in a small area from closed to @ 1/8 throttle. Did you know the N3WE is essentially the same as your NAFE, except that the taper is moved so that it runs 1.5 clip positions leaner? N3WE in clip 3 is the same as NAFE in clip 1.5. If you could move your N3WE needle a 1/2 clip leaner would it clean up 1/2 to 3/4 throttle?

If I run the N3WE in the top groove it's pretty close from 1/2 to 3/4 until the temps get above 95, and then it's too rich again. But at that setting it's too lean at around 1/4 throttle. I can cure that by upping the pilot, but then it gets blubbery at 1/8 throttle and won't idle worth a crap.

Honestly, it's actually jetted pretty close, I'm just very picky. I know it can be a little better, and it drives my OCD nuts that I can't quite get it there...

[hallsy]

If I run the N3WE in the top groove it's pretty close from 1/2 to 3/4 until the temps get above 95, and then it's too rich again. But at that setting it's too lean at around 1/4 throttle. I can cure that by upping the pilot, but then it gets blubbery at 1/8 throttle and won't idle worth a crap.

Honestly, it's actually jetted pretty close, I'm just very picky. I know it can be a little better, and it drives my OCD nuts that I can't quite get it there...

HaHa, yep when it comes to jetting these 2t's, perfection seems ever elusive.? My guess is it may not be any easier with the jd needles, but you never know until you try. I suspect for many jetting is just a pita. Learning how or bothering with it doesn't interest them they just want to know what parts to install and be done with it, nothing wrong with that. This I think is where the kits come in and shine, they are simple and basic. The directions really don't go much further than explaining how to install the parts. For these folks if the kit produces a better running bike than what they started with it's great. However if you are "very picky" the kit may come up a little short. Like willwater, my CR kit was far from plug and play for me, but it may have been perfect for someone else. Don't get me wrong, I sincerely hope your JD needles deliver, let us know how it works out. One thing I found, his customer service was awesome.

FWIW Kawasaki needle N3Y_ is 1/2 clip position leaner than N3W_.

[carlt828]

Over in the Yamaha WR sub-forum, they have developed an excellent jetting chart for the JD kit based on altitude & temps. I always thought it was JD generated, but I guess not.

[The Spanky]

FWIW Kawasaki needle N3Y_ is 1/2 clip position leaner than N3W_.

Well I don't really think I need a leaner needle per se, I need a different taper.

[Tucraysz2]

what ratio of oil/gas are you running? I had a bog issue where it would not take full throttle, everywhere else was perfect. I went from 32:1 to 40:1 and that cured it, actually helped out in all throttle positions.. just my.02 worth

[harryhandshake]

are these jd kits based on bone stock motors ? because its impossible to make a "do all" needle when you look at the nearly infinite engine mods that can be done that would affect what needle is required. if you have a pj/pwk carb theres more needles available than you could shake a stick at ( double and tripple taper available), to say you cant find one that suits your needs tells me your either lazy and dont want to invest the tuning time finding a good needle or you dont know how to tune a bike so the jet kit is a last ditch effort to make your bike run somewhat tolerable. not trying to cut down anyone but thats how i see it. and nothing agaisnt dudes that use jet kits but if you cant tune it on your own without a crutch like a jetkit then how you going to do any of the other simple maintenace/mechanical upkeep ?

Edited February 2, 2012 by harryhandshake

[Mark6299]

are these jd kits based on bone stock motors ? because its impossible to make a "do all" needle when you look at the nearly infinite engine mods that can be done that would affect what needle is required. if you have a pj/pwk carb theres more needles available than you could shake a stick at ( double and tripple taper available), to say you cant find one that suits your needs tells me your either lazy and dont want to invest the tuning time finding a good needle or you dont know how to tune a bike so the jet kit is a last ditch effort to make your bike run somewhat tolerable. not trying to cut down anyone but thats how i see it. and nothing agaisnt dudes that use jet kits but if you cant tune it on your own without a crutch like a jetkit then how you going to do any of the other simple maintenace/mechanical upkeep ?

That is correct. I do not know how to properly tune a bike. That doesn't make my lazy or stupid. I would like to learn how to properly jet a dirtbike. I looked all over and it seams like it's a big secret or very hard to find help. I doubt there are many people out there who do know. I posted a plug chop topic a few time and nobody seams to know what a good chop test looks like or how to help out. Then I read in a few places that you need to tune by feel or sound. How is that possible if you don't know how it's supposed to feel or sound. My bike seams to run great but the plug chop I had done looks a little lean. I would do just about anything to learn to tune. Where do I get this knowledge?