KX100 Jetting

[Jimbob2705]

Hi Guys,

I have a 1997 KX100 but It has the 2001 and onwards Carb fitted (Keihin PWK-28) but the previous owner put the jets from the 1997 Carb (Keihin PE-26) into this 2001+ Carb.

The problem is that they both use different jets.

The 2001+ Carb is meant to have a :

138 Main Jet

45 Pilot Jet

'NAPF' Jet Needle

60 Main Air Jet

But my 2001 Carb has :

122 Main Jet

55 Pilot Jet

(I tried to read the Jet Needle) : NBKF

No idea but probably 200 Main Air Jet (That is what the 1997 Carb would have)

Temperature would be 10 Celcius on average roughly.

The bike is standard.

What Jetting would you recommend?

Thanks and ATB!

[Jimbob2705]

I should add a bit more information about how the bike ran :

Unfortuently I haveb't been able to ride it much at all due to a clutch and oil leak problem, but I am waiting for the parts to come through to fix it.

When I did ride it though, it produced quite a lot of white smoke from the exhaust when I accelerated. Similar to this :

Today I have taken the exhaust packing out and I am going to put some new packing in soon. The old packing I took out was horrible - looked like it hadn't been changed for a while.

Was the white smoke to do with the jetting or the exhaust packing?

I know most of you will say ride it first, then change the jetting - but I seem to have quite a big difference between the recommended size jets so I thought I would ask for your advice!

Thanks and ATB!

Edited April 29, 2011 by Jimbob2705

[William1]

Not a 2s expert but I'll give my thoughts. First, if you compare the OEM specs to what you have, it does not make sense. Smaller main, larger pilot?

The logic of 2S jetting is (more or less) Adding more oil (increasing the ratio of fuel to oil, ie, 50 to 1 ---> to 30 to 1) requires richer jetting because leass gas is flowing through the jets. Make sense?

OEM jetting is based on a certain oil to fuel ratio. You know if you mis at OEM ratio and have jetting at OEM specs, the altitude is sea level, 30 inches mercury at 65 degrees and 50% humidity, it should be perfect.

So...

If you increase the oil/fuel ratio you have to jet it richer

If you decrease the oil/fuel ratio you have to jet it leaner

If it gets hotter, you have to jet it leaner

If it gets colder, you have to jet it richer

If the air pressure rise or you go down in altitude, you have to jet it richer

If the air pressure drops or you go up in altitude, you have to jet it leaner

Assuming you do not have a coolant leak, the what smoke could be the oil you are using, humidity/condensation boiling off in the pipe.

[Jimbob2705]

Not a 2s expert but I'll give my thoughts. First, if you compare the OEM specs to what you have, it does not make sense. Smaller main, larger pilot?

The logic of 2S jetting is (more or less) Adding more oil (increasing the ratio of fuel to oil, ie, 50 to 1 ---> to 30 to 1) requires richer jetting because leass gas is flowing through the jets. Make sense?

OEM jetting is based on a certain oil to fuel ratio. You know if you mis at OEM ratio and have jetting at OEM specs, the altitude is sea level, 30 inches mercury at 65 degrees and 50% humidity, it should be perfect.

So...

If you increase the oil/fuel ratio you have to jet it richer

If you decrease the oil/fuel ratio you have to jet it leaner

If it gets hotter, you have to jet it leaner

If it gets colder, you have to jet it richer

If the air pressure rise or you go down in altitude, you have to jet it richer

If the air pressure drops or you go up in altitude, you have to jet it leaner

Assuming you do not have a coolant leak, the what smoke could be the oil you are using, humidity/condensation boiling off in the pipe.

Thanks for that William! ?

I use the ratio of 32:1

As I said, the jets I have in my Carb at the moment are off a different Carb (An older model). The older OEM Carb used a smaller Main and a bigger Pilot which are now fitted into my newer OEM Carb.

So it sounds like I should change the Jets to :

138 Main Jet

45 Pilot Jet

'NAPF' Jet Needle

60 Main Air Jet

That way it would have the correct jets to suit the correct carb?

If the OEM Jetting is set at 65 degrees, what would I need to change to make it suit around 10 degrees?

Also, would I need to change anything for being at an elevation of 680ft?

Thanks for your help, I really appreciate it!

[William1]

Is the OEM ratio 32:1 also?

65 degrees is Fahrenheit, not Celcius.....

I doubt the 680 feet will matter much. But it is a combo of altitude and temp. Added to this humidity gives you Air Density. Merge Racing has som good discussions on this though I think most of the details pertain to 4S, but the big picture is the same.

Jetting for Altitude and Weather

[Jimbob2705]

Is the OEM ratio 32:1 also?

65 degrees is Fahrenheit, not Celcius.....

I doubt the 680 feet will matter much. But it is a combo of altitude and temp. Added to this humidity gives you Air Density. Merge Racing has som good discussions on this though I think most of the details pertain to 4S, but the big picture is the same.

Jetting for Altitude and Weather

The OEM ratio is 32:1

65 degrees Fahrenheit is 18.3 degrees Celsius so that is quite close. It is on average about 10 degrees Celsius here.

Regarding the Altitude and Weather :

If it gets colder, you have to jet it richer.

If the air pressure drops or you go up in altitude, you have to jet it leaner.

I was thinking, could the 680ft Elevation and the difference of 8 degrees Celsius cancel each other out?

As it is 8 degrees cooler than the OEM which means it would need to be slightly richer, and it is 680ft Elevation which means it would need to be leaner.

Thanks and ATB!?

[William1]

Based on what you've said, I think'll be just fine. Ride it and report back if there are any running issues.

[Jimbob2705]

Based on what you've said, I think'll be just fine. Ride it and report back if there are any running issues.

Thanks again William! ?

So can I just confirm this with you; I will need to get the following Jets :

138 Main Jet

45 Pilot Jet

'NAPF' Jet Needle

60 Main Air Jet

Thanks and ATVB!

[William1]

Yup, should be good.

[Jimbob2705]

Yup, should be good.

William, Thanks for confirming that! ?

Just one problem :

If I need to change the Main Air Jet which I think at the moment it is 200# but it needs to be a 60#.

The problem is that I don't know which part it is.

Can someone tell me which number on the diagram the Main Air Jet is :

?

Thanks and ATB!

[William1]

How do you know you have a #200?

[Jimbob2705]

How do you know you have a #200?

I don't but I assume I have a #200 as the previous said he changed all of the Jets over. Is there anyway I can tell or measure?

I don't even know what a 'Main Air Screw' is though?

Thanks and ATB

[Jimbob2705]

Is there anyway of telling what 'Main Air Jet' I have then?

Thanks and ATB

[crf150f guy]

The main jet on that diagram is #22. To find out what jet you have in there, you have to remove it and look at the number engraved on the jet itself.

[Jimbob2705]

The main jet on that diagram is #22. To find out what jet you have in there, you have to remove it and look at the number engraved on the jet itself.

Thanks for that but I said the 'Main Air Jet'

The manual mentions it, but yet it doesn't label it in the diagram?!

Thanks anyway! ?

[William1]

Again, how do you know the other person put in a #200? What informatio have you got to verify that? What even makes you think it?

The main air jet (and slow air jet) are located in the carb bell. On some carbs, it is a fixed jet and not removeable.

[Jimbob2705]

Again, how do you know the other person put in a #200? What informatio have you got to verify that? What even makes you think it?

The main air jet (and slow air jet) are located in the carb bell. On some carbs, it is a fixed jet and not removeable.

I don't have any information, but the previous owner said he changed the Jets over, and that was that - I don't know what Jets, but I have to assume he changed all the Jets that was possible.

I am assuming in my carb that the Main Air Jet is fixed, as I can't seem to find any information about getting a different sized jet for it.

Thanks for you help William, but I just had to make sure! ?

ATVB

James