JD Jetting Guide. Now what?

Brand JD Jetting

18 replies to this topic
  • Mark6299

Posted March 02, 2012 - 04:42 AM

#1

So I purchased the JD Jetting Guide a while back not really knowing what to expect and tried to figure it out. Am I missing something? I thought it would be a guide to help you figure out how to jet a carb. All I see is a bunch of graphs and charts. How the heck does this supposed to help someone? I guess I was wrong in thinking it would be like a dummys guide to jetting.

  • William1

Posted March 02, 2012 - 06:30 AM

#2

To use the guide, you have to know what jetting is in your bike. You have to have the bike proerly jetted for a particular day where you know the air density. Then, when the air density changes, you look on the chart to give you quick and easy baseline perfect jetting for the new conditions.
There are some books and information like this:
http://www.thumperta...ad.php?t=624773 Oring Mod and AP Tuning

http://www.dansmc.com/carbs2.htm Basic Carb Theory

http://en.wikipedia..../Density_of_air Air Density

http://tinyurl.com/6pxdoux FCR-Tuning Guide

That is more basic.

  • Kah Ran Nee

Posted March 02, 2012 - 06:53 AM

#3

So I purchased the JD Jetting Guide a while back not really knowing what to expect and tried to figure it out. Am I missing something? I thought it would be a guide to help you figure out how to jet a carb. All I see is a bunch of graphs and charts. How the heck does this supposed to help someone? I guess I was wrong in thinking it would be like a dummys guide to jetting.


James can't read your mind, so how can he solve your 'problems'?
Buy a JD Jet kit if you want the thinking done for you, as they work very well.

It's a guide to jetting, not a map.

  • thescarecrow

Posted March 02, 2012 - 08:10 AM

#4

The resources William1 posted are very useful. It takes time and practice to properly jet a bike.

I would suggest reading what you can get your hands on to get the basics down. Do a google search for "dirt bike jetting" or "dirt bike carb tuning".

I have purchased the JD Jet kits for years. I do know how to tune a carb, but with the JD kit, you get the jets and needles and, to me, is easier than trying to hunt down the parts separately.

  • Mark6299

Posted March 02, 2012 - 01:47 PM

#5

James can't read your mind, so how can he solve your 'problems'?
Buy a JD Jet kit if you want the thinking done for you, as they work very well.

It's a guide to jetting, not a map.


Have you even seen it? I don't really remember asking anyone to read my mind. I am not the first to ask this question, be it dumb or not. I don't really apreciate people like you making snobby remarks at me just because I ask a question, dumb or not. I do know how to jet a carb and have done so successfully and I have read tons of info on the subject. The only thing is that when I try to figure out the JD Jetting Guide it might as well be writting in German because it does not do a thing for me. While I am on the subject I think a LOT of people here act like they know every thing about everything when they really do not. You get these same people stating that you must get the jetting spot on. I have never ever sean people at the trails break out their jet kits and rejet their bikes because it started raining or because it got warmer by 20 degrees. If you are always in a race situation and jetting on the ragged edge of lean then I could understand that thing must be spot on. You guys scare the crap out of people with this kind of talk. What is wrong with jetting good and to be a little or lot richer. It does not make that person bad, does it?

  • William1

Posted March 02, 2012 - 04:02 PM

#6

Take a look at this link too:
http://www.mergeraci...m/tech/pandora/

  • hallsy

Posted March 02, 2012 - 04:12 PM

#7

Have you even seen it? I don't really remember asking anyone to read my mind. I am not the first to ask this question, be it dumb or not. I don't really apreciate people like you making snobby remarks at me just because I ask a question, dumb or not. I do know how to jet a carb and have done so successfully and I have read tons of info on the subject. The only thing is that when I try to figure out the JD Jetting Guide it might as well be writting in German because it does not do a thing for me. While I am on the subject I think a LOT of people here act like they know every thing about everything when they really do not. You get these same people stating that you must get the jetting spot on. I have never ever sean people at the trails break out their jet kits and rejet their bikes because it started raining or because it got warmer by 20 degrees. If you are always in a race situation and jetting on the ragged edge of lean then I could understand that thing must be spot on. You guys scare the crap out of people with this kind of talk. What is wrong with jetting good and to be a little or lot richer. It does not make that person bad, does it?

Mark I think I understand your frustration but you have to consider the possibility that these guys may not know what it is your talking about. I have the guide and do understand it to some extent but I'm a 2 stroke rider and have only looked at that section of it (PWK). If your a 2T guy then maybe I can help you, did you read through the introduction and throttle position jetting?

  • D0T-C0M

Posted March 02, 2012 - 05:00 PM

#8

Mark what carb do you have and what jetting is in it?

Edited by D0T-C0M, March 02, 2012 - 05:00 PM.


  • Mark6299

Posted March 02, 2012 - 07:50 PM

#9

Thanks guys for your help. I will indeed call on you guys if I get stumped, but I do have my jetting down ok I think. I was just saying that I don't understand the guide. I have not looked at it in depth for a while but I thought I did look at but perhaps not close enough. Any way looks like I got a couple guys willing to help instead of critisizing. So here is what I got. I thought it runs good after I richened things up a bit on the main and the needle position. Shit I have to go now. I'll be back tomorrow. got to go. Damn cat

  • D0T-C0M

Posted March 02, 2012 - 08:00 PM

#10

If you want to start by telling what type of carb do you have? If its a FCR or FCR-MX than what jetting do you have? I need that in order to help you out and show you how I use the JD charts

Edited by D0T-C0M, March 02, 2012 - 08:01 PM.


  • Kah Ran Nee

Posted March 02, 2012 - 08:28 PM

#11

Have you even seen it? I don't really remember asking anyone to read my mind. I am not the first to ask this question, be it dumb or not. I don't really apreciate people like you making snobby remarks at me just because I ask a question, dumb or not. I do know how to jet a carb and have done so successfully and I have read tons of info on the subject. The only thing is that when I try to figure out the JD Jetting Guide it might as well be writting in German because it does not do a thing for me. While I am on the subject I think a LOT of people here act like they know every thing about everything when they really do not. You get these same people stating that you must get the jetting spot on. I have never ever sean people at the trails break out their jet kits and rejet their bikes because it started raining or because it got warmer by 20 degrees. If you are always in a race situation and jetting on the ragged edge of lean then I could understand that thing must be spot on. You guys scare the crap out of people with this kind of talk. What is wrong with jetting good and to be a little or lot richer. It does not make that person bad, does it?


Just trying to understand why you are so upset over getting what you asked for.

Proper jetting requires two things, or one thing: experience and execution, or, copying someone else's experience.

The JD kit is the later, the Jetting guide is part of the former.

The best way to jet a bike, when you feel overwhelmed with information, is to copy a like bike from a like area.

Lots of posts in the forum for your specific bike, on what jetting is best for YOU.

If it's a two stroke, it's more sensitive to everything, cause their carbs have less tuning ability, so each circuit must be spot on to be right.

And yes, I see many people changing their jetting at an event, when the weather changes, or it is a new environment, if it is important to them.

If you have a four stroke, usually only altitude changes of 6,000 ft or more require a actual jetting change.

  • hallsy

Posted March 03, 2012 - 05:45 AM

#12

Just trying to understand why you are so upset over getting what you asked for.

Proper jetting requires two things, or one thing: experience and execution, or, copying someone else's experience.

The JD kit is the later, the Jetting guide is part of the former.

The best way to jet a bike, when you feel overwhelmed with information, is to copy a like bike from a like area.

Lots of posts in the forum for your specific bike, on what jetting is best for YOU.

If it's a two stroke, it's more sensitive to everything, cause their carbs have less tuning ability, so each circuit must be spot on to be right.

And yes, I see many people changing their jetting at an event, when the weather changes, or it is a new environment, if it is important to them.

If you have a four stroke, usually only altitude changes of 6,000 ft or more require a actual jetting change.


Krannie - He diden't ask for help with his jetting, he asked for help with a spreadsheet called the JD Jetting Guide. He's simply trying to understand what he's looking at on his computer and asking for help with it.

  • Chokey

Posted March 03, 2012 - 05:52 AM

#13

So I purchased the JD Jetting Guide a while back not really knowing what to expect and tried to figure it out. Am I missing something? I thought it would be a guide to help you figure out how to jet a carb. All I see is a bunch of graphs and charts. How the heck does this supposed to help someone? I guess I was wrong in thinking it would be like a dummys guide to jetting.

The guide charts are conversion charts for humidity, temperature, and altitude changes. Once you get your jetting correct for a specific set of conditions, the charts will help you determine the appropriate changes to make when conditions change.

You will still have to do the testing to determine a baseline jetting spec that is correct for the conditions during your testing.

The "search" function doesn't seem to be working right now. When it's back up search for "Spanky's jetting 101" to get a guide that will help you jet your bike.

  • Mark6299

Posted March 03, 2012 - 06:22 AM

#14

Just trying to understand why you are so upset over getting what you asked for.

Sure thing

Krannie - He diden't ask for help with his jetting, he asked for help with a spreadsheet called the JD Jetting Guide. He's simply trying to understand what he's looking at on his computer and asking for help with it.

You are spot on. Thanks for understanding what my question actually was.

The guide charts are conversion charts for humidity, temperature, and altitude changes. Once you get your jetting correct for a specific set of conditions, the charts will help you determine the appropriate changes to make when conditions change.

You will still have to do the testing to determine a baseline jetting spec that is correct for the conditions during your testing.

The "search" function doesn't seem to be working right now. When it's back up search for "Spanky's jetting 101" to get a guide that will help you jet your bike.

Now I get it. Thanks, this was the kind of answer I was hoping to get. Now I understand what the guide is for. When I purchased it, I was under the impression that you could use it step by step to jet a bike. It most definatly was not that. I simply put it aside and jetted my bikes using other literature found here on TT or as a result of being guided in the right direction. That was a while back. I just recently came back to look at the guide to revisit it and see if it made more scents. It did not, untill now. Thanks Chokey.

  • D0T-C0M

Posted March 03, 2012 - 07:36 AM

#15

I found the JD jetting guide to be very helpful when calibrating my FCR-MX carb on my XR650L. I used an wideband o2 sensor and was always getting a slight lean condition at around the 1/4 throttle mark. I used JD charts to find a needle that would fix this and put it in and it was bang on the money. Saved me lots of time and money by being able to find the exact jetting that I needed the first time. I highly recommend it, best $20 I spent doing this project. I jetted it once and than monitored my o2 sensor for a year riding at different altitudes and temperature and the jetting never needed to be tweaked so I am very happy.

  • hallsy

Posted March 03, 2012 - 08:28 AM

#16

The guide charts are conversion charts for humidity, temperature, and altitude changes. Once you get your jetting correct for a specific set of conditions, the charts will help you determine the appropriate changes to make when conditions change.

You will still have to do the testing to determine a baseline jetting spec that is correct for the conditions during your testing.

The "search" function doesn't seem to be working right now. When it's back up search for "Spanky's jetting 101" to get a guide that will help you jet your bike.

Chokey do you actualy have a copy of the JD jetting guide? Your description of it leaves me with the impression that you don't. The JD jetting guide is far more than than a simple temperature/altitude conversion chart. It in fact may teach him more about jetting than anything else other than his own hands on experience.

Mark - the guide allows you to make changes to jetting settings and then shows you how those changes will affect fuel delivery. The graph on the right will show the affect both in a percentage of change either richer or leaner, and where exactly in the throttle range that affect occurs. Changes to jetting configurations can be made in the highlighted gray boxes which include, main jet, pilot jet, needle clip postion, slide cutaway, including temperature and altitude. Along with that it also allows you to make changes to a totaly different jet needle if you so desire, the graph on the left shows the differences in the jet needle profiles. The catch is that the needle your using/inputing must be contained in the guide, if not you cant get a prediction. While there are several needles to chose from in the guide it doesn't contain them all, the JD needles aren't in the the guide. I think you may have a YZ 250, if so maybe we can run you through some quick predictions to show you just how the guide works.

  • Mark6299

Posted March 03, 2012 - 09:45 AM

#17

I triedusing the charts again. I could see that the graphs change when you input different setting but it still does not tell me anything usefull. I guess what I am trying to say is that the charts do not tell me anything. I would need to know what the goal is as far as what the graph is supposed to look like. And now where did I see anything about porting, pipes, reeds etc. Not that I have any of these but don't you think those affect jetting?

  • Chokey

Posted March 03, 2012 - 09:47 AM

#18

Chokey do you actualy have a copy of the JD jetting guide? Your description of it leaves me with the impression that you don't. The JD jetting guide is far more than than a simple temperature/altitude conversion chart. It in fact may teach him more about jetting than anything else other than his own hands on experience.

Mark - the guide allows you to make changes to jetting settings and then shows you how those changes will affect fuel delivery. The graph on the right will show the affect both in a percentage of change either richer or leaner, and where exactly in the throttle range that affect occurs. Changes to jetting configurations can be made in the highlighted gray boxes which include, main jet, pilot jet, needle clip postion, slide cutaway, including temperature and altitude. Along with that it also allows you to make changes to a totaly different jet needle if you so desire, the graph on the left shows the differences in the jet needle profiles. The catch is that the needle your using/inputing must be contained in the guide, if not you cant get a prediction. While there are several needles to chose from in the guide it doesn't contain them all, the JD needles aren't in the the guide. I think you may have a YZ 250, if so maybe we can run you through some quick predictions to show you just how the guide works.

He asked about the charts, which are conversion charts.

Yes the guide is much more than that. It doesn't invalidate my response.

  • hallsy

Posted March 10, 2012 - 09:23 AM

#19

I triedusing the charts again. I could see that the graphs change when you input different setting but it still does not tell me anything usefull. I guess what I am trying to say is that the charts do not tell me anything. I would need to know what the goal is as far as what the graph is supposed to look like. And now where did I see anything about porting, pipes, reeds etc. Not that I have any of these but don't you think those affect jetting?


Mark - Maybe this will help, maybe not, by now you may not care. The info you enter in line #1 of the boxes shows up on the chart/graph as a heavy black line.
The info you enter in the boxes on the input lines that follow (line #2 through #5) shows up on the graph as it compares to the input for line #1. Thus the graph provides you with a comparison.
The entries for each line are sumurized and conviently located in the box within the graph. They are also color coded which makes for easy reference and comparisons. Try inputing your current jetting configuration on line #1 and follow that with the same identical inputs for lines 2 thru 5. With that done you'll notice that you still only have 1 line in each graph, if not you have an input that isn't the same somewhere.
One of the most important things that you would have taken from any jetting tutorial is that jetting is throttle position sensative (think slide height). Both of the JD graphs are set up with the throttle position across the bottom of the graph (0,1/8,1/4,3/8,1/2,5/8,3/4,7/8 and 1).
Now make some changes to the inputs to line 2 through 5 but limit them to one component and one size leaner or richer for that component, ( a big change in a component can move the line off the graph. LOL) Start by changing just your pilot size input on line 2, my line 2 shows upon the graph in blue, this blue line indicates where and what that change amounts to. The portion of a colored line that shows up above the black line in the graph = richer and the portion below the black line = leaner. On line 3 change just your main jet size, my line 3 shows up in green. If your on the PWK graph then on line 4 try just a slide change, my line 4 shows up in red. Up to this point nothing should have happened in the graph on the left (needle profile) because the needle profile hasn't changed. On line 5 change just the clip position, my line 5 shows up in purple.
I had you change 1 item per line so the current graph should give you a good indication of where (throttle range) and how much (%increase/decrease) those individual carb component effects jetting, but your not limited to one item per line. The graph will show the combined effects of all the changes you make to an input line.
Notice that with the clip position change you also have a purple line in the needle profile graph even though you didn't change to a different needle. That's because a clip position change moves the needle taper location as it relates to the slide. The taper location is only one of several ways a needles profile can change. The needle profile graph indicates the differences in needle profiles by graphing the diameter of a needle (numbers on the left) at different throttle positions. I think the reason both DOT- COM and I asked you questions regarding your particular bike/jetting is so that we might provide you with info you could relate to. If you ever get to a point where you feel a different needle is what your after the profile graph and selection of needles in the guide may be helpful. Sounds like DOT-COM was able to find what he was after on his first try.





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