Jetting crossover chart
06-13-2009, 05:01 AM
#1
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06-13-2009, 11:47 AM
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mikstr;
Thanks for posting it and I think an accurate jet cross reference would be nice to have.
I just can't believe some of the one at the link.
I've got street baffle cans, OEM air filter, bone stock motor and Dynojet mains 175f/180r.
Bike runs perfect, plugs look like the "best" picture in the spark plug brochures.
According to that chart I went from the the stock 175f/178r Keihin mains to the Dynojet equivalent of 196.5/202 Keihin mains. That doesn't make sense to me.
A Keihin 202 and a Dynojet 180 might have the same orifice diameter but there is no way they have the same flow rate.
Thanks for posting it and I think an accurate jet cross reference would be nice to have.
I just can't believe some of the one at the link.
I've got street baffle cans, OEM air filter, bone stock motor and Dynojet mains 175f/180r.
Bike runs perfect, plugs look like the "best" picture in the spark plug brochures.
According to that chart I went from the the stock 175f/178r Keihin mains to the Dynojet equivalent of 196.5/202 Keihin mains. That doesn't make sense to me.
A Keihin 202 and a Dynojet 180 might have the same orifice diameter but there is no way they have the same flow rate.
06-13-2009, 01:51 PM
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I can't remember the details, but I've read some main jets are numbered based on inner diameter and some are based on flow rate.
I've never seen a cross reference I had confidence in, but that in itself is worth discussing and hashing out.
06-13-2009, 02:00 PM
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Old Info
That information may be a bit outdated. I talked with a bike tuner last year, while trying to dial in my old GS1000, and mentioned the differences between Keihin and DJ jet sizes. What he said is that about 20 years ago the jets had different sizes but DJ later changed their sizing scheme to correspond with Keihin. He said that when tuning carbed bikes now he uses DJ and Keihin jets completely interchangeably without any issues whatsoever.
06-13-2009, 06:35 PM
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Yeah. I don't remember which is which. I just remember the Keihin and DJ numbers don't correlate. If somebody would test the flow rate of every jet size by Keihin and DJ and compare them, that would be useful. As far as I can tell, nobody has ever done that.
06-13-2009, 06:44 PM
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06-13-2009, 06:58 PM
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Another thing;
Given the differences in ID, shape and length, I think it possible that two different main jets which flow exactly the same at 3k rpm might flow differently at 6k at 9k rpm.
DJ claims essentially this. It might be proprietary protecting BS, but it might be 100% accurate.
Given the differences in ID, shape and length, I think it possible that two different main jets which flow exactly the same at 3k rpm might flow differently at 6k at 9k rpm.
DJ claims essentially this. It might be proprietary protecting BS, but it might be 100% accurate.
06-13-2009, 10:35 PM
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(shop trick wisdom)
Get a set of pin-guages or jet-drills as a benchmark.
Insert the pin guages until you get tight fit, and write down the #.
Base all your jetting on this size standard and it wont matter what you mix and match.
It could be written in russian or chinese and you will still be the master of the situation.
Get a set of pin-guages or jet-drills as a benchmark.
Insert the pin guages until you get tight fit, and write down the #.
Base all your jetting on this size standard and it wont matter what you mix and match.
It could be written in russian or chinese and you will still be the master of the situation.
05-24-2012, 05:27 PM
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Resurrection
I had a short discussion earlier in which main jet orifices were brought up. I had previously (several years ago) held several jets up to light to try and gauge the different sizes by looking through each one and *thought* that the Keihin vs DJ looked very very close in relation to the numbering listed on each jet.
Today I became curious so went around looking for various things to use as a jet gauge. Nails, hex keys, pins, needles, paperclips, precision screwdrivers, plastic dart tips, and torch tip cleaners. The jets available were DynoJet 190 and 185, and Keihin 180.
I was able to pass one particular screwdriver shank through the DJ190, but it would NOT go through either of the other 2. Then used a 1/16" hex key that the K 180 fit onto easily with room to spare and a SLIGHT wobble. The DJ 185 also fit the hex key but had a tiny bit more wobble. The DJ 185 is apparently larger than the K 180.
Micrometer shows screwdriver shank 1.89mm and the hex key 1.74mm at widest point.
So, for those of you who have installed DJ mains on a stock setup in place of the Keihin mains with similar numbers and have good spark plug coloring, it seems to be because they ARE THE SAME ******* SIZE.
I cannot measure the flow rate except by putting the mains in and seeing how the engine behaves. So the DJ could flow more at higher speed or more at lower speed, but judging from my experience this is not the case. Well, maybe they do flow more at low speed. The dyno charts usually show a rich flat area in the torque curve around 4-6k when DynoJet kits are installed and set for best allover performance.
So all those charts on various websites showing jet sizing cross reference, which were mostly written long ago, seem to have some seriously erroneous data.
Any thoughts?
Today I became curious so went around looking for various things to use as a jet gauge. Nails, hex keys, pins, needles, paperclips, precision screwdrivers, plastic dart tips, and torch tip cleaners. The jets available were DynoJet 190 and 185, and Keihin 180.
I was able to pass one particular screwdriver shank through the DJ190, but it would NOT go through either of the other 2. Then used a 1/16" hex key that the K 180 fit onto easily with room to spare and a SLIGHT wobble. The DJ 185 also fit the hex key but had a tiny bit more wobble. The DJ 185 is apparently larger than the K 180.
Micrometer shows screwdriver shank 1.89mm and the hex key 1.74mm at widest point.
So, for those of you who have installed DJ mains on a stock setup in place of the Keihin mains with similar numbers and have good spark plug coloring, it seems to be because they ARE THE SAME ******* SIZE.
I cannot measure the flow rate except by putting the mains in and seeing how the engine behaves. So the DJ could flow more at higher speed or more at lower speed, but judging from my experience this is not the case. Well, maybe they do flow more at low speed. The dyno charts usually show a rich flat area in the torque curve around 4-6k when DynoJet kits are installed and set for best allover performance.
So all those charts on various websites showing jet sizing cross reference, which were mostly written long ago, seem to have some seriously erroneous data.
Any thoughts?
05-24-2012, 06:42 PM
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- We are often asked for a "cross reference" sheet that compares our main jets to Mikuni or Keihin. The fact is you cannot directly interchange the jets for a given size. Many things affect fuel flow through a jet of the same orifice size. The entry and exit tapers of our main jets differ from those of other companies. Due to this, the fuel flow changes as a function of velocity through the carburetor venturie. This means that two jets of equal orifice size will have a different fuel flow curve relative to intake air speed. At a certain speed the two may flow equally, but a change in velocity changes the flow characteristics. The Dynojet main jet hole size is measured in millimeters. For example, a DJ142 has a 1.42mm hole.
Dynojet Research & Development So by this we get
1) DynoJet - Measured in mm
2) Keihin - Jets are measured using an unknown convention. Measurements are based on orifice diameter size. I have never seen anything that actually lists how they measure
3) Mikuni - Available in 2.5 increments. Mikuni uses yet another measurement convention - reportedly based on flow rate. The result is that Mikuni's sizes are vastly different from the other makers'.
So no they are not the same.....sorry and the cross reference you hate so much does clearly show that when measured pin gauge with a pin they have different size holes for the same number jet from each manufacturer.
As Mr Cory stated, the enter and exit tapers can also be different which also changes things.
05-24-2012, 07:05 PM
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Interesting, Mr.Coffee suggests that I use his brand of cleaning agent when my coffee maker is not working correctly. But, plain white vinegar works just the same.
Well, perhaps my measuring methods are not accurate enough for conclusive evidence. I see the numbers matching up within .05mm at most. How would a pin gauge show a difference of .20mm in an orifice that is the same diameter +/- .05?
Well, perhaps my measuring methods are not accurate enough for conclusive evidence. I see the numbers matching up within .05mm at most. How would a pin gauge show a difference of .20mm in an orifice that is the same diameter +/- .05?
05-24-2012, 08:44 PM
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Well tell you what, you can contact Mr Cory at DynoJet and he can explain it to you.
He clearly states the even if the hole is the same size the flow will be different even though you say different.
As for your measurements, as you don't have any jets to measure with the same number so that is the first flaw.
Then you state that a 185 DJ is larger than a 180 Keihin, well yes it is and the chart even says so which is also what I had stated.
As for the "wobble" by the chart a Keihin 180 jet has a .0700 orifice and a 185 DJ has a .0820 orifice (which is the same as a 210 keihin jet) so wouldn't .012" produce the wobble you were talking about.
We are talking steps of approx. .001" between jet sizes. so unless you have a set of pin gauges you can not get accurate measurements. Sorry a hex key just will not cut it here.
So to tell the truth it really isn't worth the time to argue about.
Believe what you want. think they "ARE ALL THE SAME ******* SIZE" to use your words but it's a free country and I will believe what I want which is they are different and you sticking a hex key in a jet and saying this one wobbles a little and that one wobbles a little more will not get me to change my mind, sorry.
If you would like to discuss this in a civil manner, no problem but the language and the Mr. Coffee type analogizes seem to be a bit confrontational and more just wanting to argue not present real data.
So you win..... here is a cookie and have a nice day
He clearly states the even if the hole is the same size the flow will be different even though you say different.
As for your measurements, as you don't have any jets to measure with the same number so that is the first flaw.
Then you state that a 185 DJ is larger than a 180 Keihin, well yes it is and the chart even says so which is also what I had stated.
As for the "wobble" by the chart a Keihin 180 jet has a .0700 orifice and a 185 DJ has a .0820 orifice (which is the same as a 210 keihin jet) so wouldn't .012" produce the wobble you were talking about.
We are talking steps of approx. .001" between jet sizes. so unless you have a set of pin gauges you can not get accurate measurements. Sorry a hex key just will not cut it here.
So to tell the truth it really isn't worth the time to argue about.
Believe what you want. think they "ARE ALL THE SAME ******* SIZE" to use your words but it's a free country and I will believe what I want which is they are different and you sticking a hex key in a jet and saying this one wobbles a little and that one wobbles a little more will not get me to change my mind, sorry.
If you would like to discuss this in a civil manner, no problem but the language and the Mr. Coffee type analogizes seem to be a bit confrontational and more just wanting to argue not present real data.
So you win..... here is a cookie and have a nice day
05-24-2012, 09:09 PM
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I am really trying to comprehend what it is that you are trying to explain to me, but you keep giving me conflicting numbers.
If I read the chart from left to right, a 180 Keihin has the same orifice size as a DJ 162. Is this correct?
If I read the chart from left to right, a 180 Keihin has the same orifice size as a DJ 162. Is this correct?
05-25-2012, 12:16 AM
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Keihin jets are measured by the orfice size. A 180 jet is 1.80mm in diameter. Mikuni as I recall uses flow rates but it's been a long time since I learned about which was which I don't recall exactly what the measurements represent. I do recall from jetting anything from a TRX400EX to R6's and pretty much anything in between the the Dynojet jets were off and unless you had a pile of dynojet specific jets it's pointless to try to jet anything with them. That's why I've always hated messing with dynojet kits. If you jet it and are ever out anywhere and it needs to be changed you're fowled as places don't usually stock DJ jets but they're likely to have Keihin jets. This isn't nearly as critical when jetting something like our SH's being they don't really need jetting changes much but when you're jetting dirt bikes or quads that are more affected by weather and altitude changes it could be a factor.
05-25-2012, 04:43 AM
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I have taken measurements using various steel shafts as pin gauges and then measured the shafts with a metric micrometer, and have found both of these statements to be true:
The topic of discussion is the jetting crossover chart and several comments were made questioning the accuracy of the chart.
I measured the DJ190 with certainty that it is 1.90mm (.0748in). The DJ185 seems to be about .05mm smaller than the 190 which would put it at 1.85mm (.0728). And the Keihin 180 fits fairly closely to a shaft measuring 1.75mm making it about 1.80mm (.0708in).
The chart shows a DJ142 measuring (.0600 in) = 1.52 mm which is wrong by Mr. Cory's information. It also shows a DJ190 at (.0840) in = 2.13 mm which is wrong according to my measurement, which is a difference of .0092 in. That would be NINE jet sizes off.
The conclusions I can draw from this are:
1. Both Keihin and DynoJet mark their jets according to orifice diameter, and the crossover chart clearly does not show this to be true. Therefore,
2. the chart is flawed in regard to DJ sizing.
3. The Keihin sizing appears correct on the chart.
4. Anyone who blindly follows this chart could make some really serious jetting errors.
I have not measured Mikuni jets since they would not be useable on the SuperHawk That and I only have one set that are 34 years old. These may not correlate with current numbering.
I measured the DJ190 with certainty that it is 1.90mm (.0748in). The DJ185 seems to be about .05mm smaller than the 190 which would put it at 1.85mm (.0728). And the Keihin 180 fits fairly closely to a shaft measuring 1.75mm making it about 1.80mm (.0708in).
The chart shows a DJ142 measuring (.0600 in) = 1.52 mm which is wrong by Mr. Cory's information. It also shows a DJ190 at (.0840) in = 2.13 mm which is wrong according to my measurement, which is a difference of .0092 in. That would be NINE jet sizes off.
The conclusions I can draw from this are:
1. Both Keihin and DynoJet mark their jets according to orifice diameter, and the crossover chart clearly does not show this to be true. Therefore,
2. the chart is flawed in regard to DJ sizing.
3. The Keihin sizing appears correct on the chart.
4. Anyone who blindly follows this chart could make some really serious jetting errors.
I have not measured Mikuni jets since they would not be useable on the SuperHawk That and I only have one set that are 34 years old. These may not correlate with current numbering.
05-25-2012, 09:35 AM
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If you want to believe that ever jet made by every manufacturer is the same and are completely interchangeable, fine you are free to do so.
If you wish to swap needles and jets and any other bits from whatever manufacturer you want, fine, its your bike, do whatever you want.
If you want to believe that even if the numbers match and even if the hole size matches the flow rates can be different (like DynoJet claims) that is fine also.
If you want to believe that certain needles are designed to work with certain jets, that is fine. Also if you wish to believe any needle will work just fine with any jet, that is fine too.
If you wish to scream obscenities or use off the wall analogize, feeling that it makes your point of view more true, feel free.
I really don't have the time to just sit and argue with people.
So Like I said:
So you win..... here is a cookie and have a nice day
If you wish to swap needles and jets and any other bits from whatever manufacturer you want, fine, its your bike, do whatever you want.
If you want to believe that even if the numbers match and even if the hole size matches the flow rates can be different (like DynoJet claims) that is fine also.
If you want to believe that certain needles are designed to work with certain jets, that is fine. Also if you wish to believe any needle will work just fine with any jet, that is fine too.
If you wish to scream obscenities or use off the wall analogize, feeling that it makes your point of view more true, feel free.
I really don't have the time to just sit and argue with people.
So Like I said:
So you win..... here is a cookie and have a nice day
05-25-2012, 10:13 PM
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That is actually really funny. I bring hard data to the table and you keep bringing...cookies. 
I really do not know what cookies have to do with anything here.
Still, I like you Bro.
We ARE having a nice civil discussion. I made a comparison in a HUMOROUS way to demonstrate: a company representative will usually promote his brand EVEN THOUGH he knows a competitor's product will work equally well. Mr. Cory even stated that Keihin jets are numbered by an unknown system. But, it is his business to know what the industry standards are in order to try, and make, improvements. One could surmise 2 things by his word usage. He either really does not know the actual sizing of Keihin (unlikely since his jets use the exact same sizing), which would suggest very poor testing procedures. Or, more likely, he wants us to believe that he does not know what it is that he actually knows, so that we will keep buying his products since they are supposedly better.
As for what I believe, I believe in testable repeatable scientific analysis and the promotion of accurate data so that we ALL may benefit.
In my opinion, and it is just that - an opinion: the reason why many people have so much difficulty tuning the DynoJet kit for our bikes is the main jets offered. DJ skips every other size(170 175 180). So, the rear main will be one size richer than optimal. This shows up on the dyno pull graph as a flat area with overly rich A/F. A possible fix (possible) is to use alternate mains that have tighter sizing differences (172 175 178). It is also very likely that the flow rate at lower velocities IS different, but at a higher velocity they are pretty much the same.
If I accidentally clicked on that cookie image, will my computer be infected by a virus? I hope not, because I clicked it. Accidentally.
I really do not know what cookies have to do with anything here.Still, I like you Bro.
We ARE having a nice civil discussion. I made a comparison in a HUMOROUS way to demonstrate: a company representative will usually promote his brand EVEN THOUGH he knows a competitor's product will work equally well. Mr. Cory even stated that Keihin jets are numbered by an unknown system. But, it is his business to know what the industry standards are in order to try, and make, improvements. One could surmise 2 things by his word usage. He either really does not know the actual sizing of Keihin (unlikely since his jets use the exact same sizing), which would suggest very poor testing procedures. Or, more likely, he wants us to believe that he does not know what it is that he actually knows, so that we will keep buying his products since they are supposedly better.
As for what I believe, I believe in testable repeatable scientific analysis and the promotion of accurate data so that we ALL may benefit.
In my opinion, and it is just that - an opinion: the reason why many people have so much difficulty tuning the DynoJet kit for our bikes is the main jets offered. DJ skips every other size(170 175 180). So, the rear main will be one size richer than optimal. This shows up on the dyno pull graph as a flat area with overly rich A/F. A possible fix (possible) is to use alternate mains that have tighter sizing differences (172 175 178). It is also very likely that the flow rate at lower velocities IS different, but at a higher velocity they are pretty much the same.
If I accidentally clicked on that cookie image, will my computer be infected by a virus? I hope not, because I clicked it. Accidentally.
05-25-2012, 10:39 PM
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But,
How about how the jet interacts with the needle? Does that have any play? Especially when you consider the inlet shape or overall profile of the hole? Fluid will flow differently if it is slightly shaped like a funnel rather than a straight cylinder, while shoving stuff in the hole won't necessarily show you this. How about at different vacuums or rpm's? Does this play a part in how the jet acts? How tight are the tolerances? Shoot, even the material or finish of the jets could have an effect.
I have no idea what the answers to these are, but I personally don't think that any of these questions have been answered in this thread yet...
But I would love to learn!
BTW I clicked on the cookie, so I have the virus too
05-26-2012, 09:47 AM
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The reason I will not continue with this is I see many flaws in what you claim as "Hard Data"
First is the "claim" that Keihin jets are sized in mm like DJ.
Is there any documentation to prove this? As in my dealings with Keihin I have always been told they use a proprietary measuring system.
So unless this can be proved. it is not "hard data" just someone claiming it to be true.
Second is your measuring system. You stated that you found various items to stick down the jets, then measured them.
My question here is do you know how easy it is to actually damage a brass jet by sticking stuff down them? Even if you cause only .0005" of damage, after two tries you have now changed the jet size by approx. 1 jet size.
not saying that you did cause damage but can you be 100% sure that you didn't?
Then you said you used the amount of "wobble" to justify that the jets had to be the same. In that claim you first tested a Keihin 180 and then a DJ 185. So even if they were measured the same way, there should have been .05mm or .0019" difference between them.
So exactly how much more "wobble" would .001" on each side of your measuring device produce.
Then your "sample size" is not really something that can be used for "hard data". You (by your claim) only have 3 jets to measure, none of which are marked the same size.
So these reasons, along with DJ themselves stating they don't know how Keihin is measured (which if they were the same you would think they would say that-FactoryPro makes that claim, so if they are truly interchangeable why would DJ say they are not? ) are why I don't believe it is really worth the time to continue this topic.
Plus DJ statement that their jets flow different even if the size is the same is another sticky point.
So if you can actually produce some true "hard data" then we can discuss this. As it stands now all I see is opinions and what is the point of carrying on from here.
No I didn't even bother with needles or any other part because unless there is actual "hard data" on the jets how is it possible to discuss how different needles have different tapers to work properly with the different flow rates.
First is the "claim" that Keihin jets are sized in mm like DJ.
Is there any documentation to prove this? As in my dealings with Keihin I have always been told they use a proprietary measuring system.
So unless this can be proved. it is not "hard data" just someone claiming it to be true.
Second is your measuring system. You stated that you found various items to stick down the jets, then measured them.
My question here is do you know how easy it is to actually damage a brass jet by sticking stuff down them? Even if you cause only .0005" of damage, after two tries you have now changed the jet size by approx. 1 jet size.
not saying that you did cause damage but can you be 100% sure that you didn't?
Then you said you used the amount of "wobble" to justify that the jets had to be the same. In that claim you first tested a Keihin 180 and then a DJ 185. So even if they were measured the same way, there should have been .05mm or .0019" difference between them.
So exactly how much more "wobble" would .001" on each side of your measuring device produce.
Then your "sample size" is not really something that can be used for "hard data". You (by your claim) only have 3 jets to measure, none of which are marked the same size.
So these reasons, along with DJ themselves stating they don't know how Keihin is measured (which if they were the same you would think they would say that-FactoryPro makes that claim, so if they are truly interchangeable why would DJ say they are not? ) are why I don't believe it is really worth the time to continue this topic.
Plus DJ statement that their jets flow different even if the size is the same is another sticky point.
So if you can actually produce some true "hard data" then we can discuss this. As it stands now all I see is opinions and what is the point of carrying on from here.
No I didn't even bother with needles or any other part because unless there is actual "hard data" on the jets how is it possible to discuss how different needles have different tapers to work properly with the different flow rates.
05-26-2012, 08:52 PM
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I am with you, as I have questions also. I honestly do not know how the other sections of the main jet affect flow rates. But, based on my research and knowledge of the world in general, I tend to think that the orifice size is the single largest determining factor in flow rate. If other factors do play a role they may be too small to be of any significance. And if the flow rate is the same given 2 jets of different manufacture with the same orifice size, then needle taper plays its own role, and it would not care what symbol happens to be on the main jet.
Another variable that could play into the equation is the depth of the main jet below the fuel level. The DJ mains do have a taller mouth, so they might receive higher fuel pressure.
Also, as for marketing, I am not saying for certain that DynoJet is wrong or is lying, but there is room for doubt, given their motives.
The reason I will not continue with this is I see many flaws in what you claim as "Hard Data"
First is the "claim" that Keihin jets are sized in mm like DJ.
Is there any documentation to prove this? As in my dealings with Keihin I have always been told they use a proprietary measuring system.
So unless this can be proved. it is not "hard data" just someone claiming it to be true....
....
So if you can actually produce some true "hard data" then we can discuss this. As it stands now all I see is opinions and what is the point of carrying on from here.
No I didn't even bother with needles or any other part because unless there is actual "hard data" on the jets how is it possible to discuss how different needles have different tapers to work properly with the different flow rates.
First is the "claim" that Keihin jets are sized in mm like DJ.
Is there any documentation to prove this? As in my dealings with Keihin I have always been told they use a proprietary measuring system.
So unless this can be proved. it is not "hard data" just someone claiming it to be true....
....
So if you can actually produce some true "hard data" then we can discuss this. As it stands now all I see is opinions and what is the point of carrying on from here.
No I didn't even bother with needles or any other part because unless there is actual "hard data" on the jets how is it possible to discuss how different needles have different tapers to work properly with the different flow rates.
That is right, needle taper may not be relevant to this discussion.
It just occurred to me that another chart is available that lists the diameter for each jet size. It was not posted in this thread, but you Sir did provide it to me earlier. The numbering corresponds closely to the chart referenced in the OP. This should illustrate well for anyone who may be confused.
Carb Jet Size Cross Reference
Here is a small section of the chart that shows jets we are all familiar with.
Width------Keihin # -- DynoJets # -- Mikuni #
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
Now if we take Mr. Cory at his word that DJ is sized in mm, and then convert the inch units on the chart to metric, we see:
Width------Keihin # -- DynoJets # -- Mikuni #
1.73 ---- 175--------- 158--------- 148.1
1.75 ---- 177.5------- 160--------- 150.0
1.78 ---- 180--------- 162--------- 151.9
1.80 ---- 182.5------- 164--------- 153.8
1.83 ---- 185--------- 166--------- 155.6
1.85 ---- 187.5------- 168--------- 157.5
1.88 ---- 190--------- 170--------- 159.4
The chart's Inadequacy becomes clear.
So this raises more questions. Do we throw out the chart entirely? Or can we make revisions that depict reality?
As for my method of measurement, I am very capable of determining what it is that I have in my hands. I am also very much aware how delicate brass is and the possible effects of even miniscule irregularities in the orifice. One thing to note, however, is the large size of these mains. If I were to lightly scratch a pilot jet the effects would be very dramatic. These mains are huge. A small scratch would be MUCH less dynamic.
And no, I certainly did not shove anything into any jets. I simply passed rods very carefully through, much like you would when using a feeler gauge when measuring valves. I know it is quite a different thing, but still the process is similar. Hold the rod straight up, put the jet centered on the rod and see if gravity wins.
05-29-2012, 02:22 PM
#25
Seasoned tech
SuperSport
Join Date: Apr 2012
Location: Issaquah, WA
Posts: 576
Well I know for a fact that the jetting is not the same between Keihin and DJ jets. I've seen it first hand in jetting bikes. Now weather the actual orfice size is different or the way the jet flows is different I'm not sure. If the taper in the jet is different or is shaped different it will all affect flow. Now why someone would want to do something to increase flow on a jet is beyond me. It will just confuse those trying to use them as DJ has seemed to accomplish in doing. I have a feeling it's more for propriatary reasons as in if you have DJ jets and you want to jet your bike for it to make any sense you'd need to purchase more DJ jets.
No offesne but I do have to agree with Hawk on your sizing methods. You need to use precise pin gauges with the correct known size to be accurate enough to say for sure and using the "wobble" from one to the next is hardly scientific. While I will agree with you that you should be able to get a close idea unless you're actually using pin gauges you're leaving enough room for error that I'd say could vary by at least one size. It's kind of like finding various sized flat objects, such as a piece of paper, a match book cover, etc, measureing them then trying to use them to check your valve clearance. Yeah you could get close but it's really not that accurate.
No offesne but I do have to agree with Hawk on your sizing methods. You need to use precise pin gauges with the correct known size to be accurate enough to say for sure and using the "wobble" from one to the next is hardly scientific. While I will agree with you that you should be able to get a close idea unless you're actually using pin gauges you're leaving enough room for error that I'd say could vary by at least one size. It's kind of like finding various sized flat objects, such as a piece of paper, a match book cover, etc, measureing them then trying to use them to check your valve clearance. Yeah you could get close but it's really not that accurate.
05-30-2012, 12:05 AM
#26
Slacker
Superstock
Superstock
Join Date: Jun 2005
Location: San Antonio, TX
Posts: 489
The bevel in the jets are certainly different. The DJ has almost no bevel and a narrower bore on both ends. It is very likely that these differences could affect flow rates. How much effect? Judging by the engine performance 
I would say it is very little.
But, I am convinced that the orifice is NEARLY the same between the 2 brands based on jet size. If there is any variation between the two, it is only a matter of .01-.02 mm.
I setup a demonstration to illustrate various jet orifice sizes, an indirect means of measurement by way of direct comparison. The thought occurred to me while I was using a dart tip to judge the different orifice sizes. If I had the same numbered jets on hand from each supplier, I would have used them in the experiment. But, the stepping in the pictures does show rather well how each orifice compares to the next.
I have on hand 11 jets from 4 manufacturers for the demonstration. It may not be scientific enough for some, but I found it interesting. This should help you see with your eyes what I have seen with my tools.
Jet Designations D= DynoJet, K= Keihin, G= Generic, M= Mikuni
Orifice mouth is approximately 2.65mm up from the base on both D and K jets.
^ D190, D185, K180, K175 ^
For reference, the needle diameter measured 210mm just below the BASE of the D190. According to the chart, the 190 should be much lower than it is.
^ K128, G124, G118, D116 ^
^ D142, G140, K128, D116 ^
^ D190, D142, D116, M102 ^
Note the Mikuni is really close to the 116, and going by the chart this would correlate. However, I did not measure the orifice mouth depth on the Mikuni. The DJ numbers on the chart seem to be very wrong.
What I am after? I switched to Keihin mains for the closer sizing (besides that, my bike came with the kit installed and no extra parts). If I need to go up or down a size or two in order to get a comparable flow rate then no problem. The performance will tell me.
So what do you guys think, am I nuts?
I would say it is very little. But, I am convinced that the orifice is NEARLY the same between the 2 brands based on jet size. If there is any variation between the two, it is only a matter of .01-.02 mm.
I setup a demonstration to illustrate various jet orifice sizes, an indirect means of measurement by way of direct comparison. The thought occurred to me while I was using a dart tip to judge the different orifice sizes. If I had the same numbered jets on hand from each supplier, I would have used them in the experiment. But, the stepping in the pictures does show rather well how each orifice compares to the next.
I have on hand 11 jets from 4 manufacturers for the demonstration. It may not be scientific enough for some, but I found it interesting. This should help you see with your eyes what I have seen with my tools.
Jet Designations D= DynoJet, K= Keihin, G= Generic, M= Mikuni
Orifice mouth is approximately 2.65mm up from the base on both D and K jets.
^ D190, D185, K180, K175 ^
For reference, the needle diameter measured 210mm just below the BASE of the D190. According to the chart, the 190 should be much lower than it is.
^ K128, G124, G118, D116 ^
^ D142, G140, K128, D116 ^
^ D190, D142, D116, M102 ^
Note the Mikuni is really close to the 116, and going by the chart this would correlate. However, I did not measure the orifice mouth depth on the Mikuni. The DJ numbers on the chart seem to be very wrong.
What I am after? I switched to Keihin mains for the closer sizing (besides that, my bike came with the kit installed and no extra parts). If I need to go up or down a size or two in order to get a comparable flow rate then no problem. The performance will tell me.
So what do you guys think, am I nuts?
05-30-2012, 09:14 AM
#27
Senior Member
MotoGP
Join Date: Jul 2010
Location: Phoenix, AZ
Posts: 3,869
But it seems just a little too easy to write it off as marketing and saying that hole size is good enough. It could be...
Here's my thought: They've found that the little tubercles are more than just abnormalities on whale fins. Those little bumps make the fins less prone to stalling. It's an old article, but they're using these findings on airplane wings now:
Whale-Inspired Wind Turbines - Technology Review
What I'm getting at is that fluid- and aero- dynamics aren't simple (things you wouldn't think important have hidden effects), and myself personally wouldn't use your findings as anything concrete without more info. In reality, we're looking for the effects on a dyno/ in the real world and I may be overly critical, but every time I take something at face value it comes back to bite me
05-30-2012, 09:52 AM
#28
Seasoned tech
SuperSport
Join Date: Apr 2012
Location: Issaquah, WA
Posts: 576
I think your findings are very interesting. The only flaw I see to them is you don't really have the same sizes in any of the different brands to directly compare. But the depth on the needles does give a good comparasin to the hole diameter. I do find it interesting how the D185 seems smaller than the K180.
I think due to that we've got two things at play here, 1) the orfice size and 2) the orfice shape which affects flow that the ONLY way to really compare is to put them both in the bike and see which two jets make the bike run the same then see what the numbers are.
As a side thought I highly doubt they will be perfectly the same so two comperable jets may actually be say a half size different between a D and K jet. If one did enough research to find the correlation this may be a way to better fine tune the bike if say a K180 is slightly to big but a K178 is slightly to small. A D 162 jet (using reference from the chart just as an example) may actually fall between those two and help get the jetting dead on.
I think due to that we've got two things at play here, 1) the orfice size and 2) the orfice shape which affects flow that the ONLY way to really compare is to put them both in the bike and see which two jets make the bike run the same then see what the numbers are.
As a side thought I highly doubt they will be perfectly the same so two comperable jets may actually be say a half size different between a D and K jet. If one did enough research to find the correlation this may be a way to better fine tune the bike if say a K180 is slightly to big but a K178 is slightly to small. A D 162 jet (using reference from the chart just as an example) may actually fall between those two and help get the jetting dead on.
05-30-2012, 09:56 AM
#29
Banned
MotoGP
Join Date: Aug 2007
Location: Lake View Terrace, CA
Posts: 5,942
Can I ask why the needles you have pictured are different lengths? By your pic #1 & #3 are one length and #2 & #4 are a different length.
So as the lengths are different it would be difficult to say, without an optical comparator, if the taper is the same which means your pics really don't prove anything one way or the other.
So you guys can argue all you want and I really didn't want to post anything, it just looked like a point that needed to be brought up.
So as the lengths are different it would be difficult to say, without an optical comparator, if the taper is the same which means your pics really don't prove anything one way or the other.
So you guys can argue all you want and I really didn't want to post anything, it just looked like a point that needed to be brought up.
