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Main Air Screw? Do you mean the Main jet?

Sorry, I meant Main Air Jet!

Thanks for pointing out my mistake! :thumbsup:

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What kind of bike is this for? Going from a 200 main to a 60? Something doesn't sound right about this. The only jet that works with the air screw, is the pilot jet.

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What kind of bike is this for? Going from a 200 main to a 60? Something doesn't sound right about this. The only jet that works with the air screw, is the pilot jet.

Here's the main thread about it : http://www.thumpertalk.com/forum/showthread.php?t=978322

If you read the 1st post by me you will see why I want to change it.

I need to know which part it is, so I can change it!

Thanks and ATB!

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I think there might possibly be a little bit of confusion on what the different circuits, and their parts, get called...... It sounds like you're possibly trying to make changes to a couple of different circuits, and maybe are a little confused about which does what, what they're called, & etc.?

Like was said above, going from a #200 to a #60 main jet is a HUGE difference; one that could possibly cause some serious engine problems if the 200 main jet was reasonably close to the correct size..... Unless you plan on never opening your throttle wide open again.... :thumbsup:

First of all, what is your bike "doing" wrong that makes you feel it needs some brass swapped around, JimBob? What kinda bike is it, size, year, & etc.?

Now, if you're having problems with "barely open" throttle positions, the only air-to-fuel mixture screw that carb shows is for the slow speed/low throttle opening circuit. It basically works from idle to around 3/8 throttle opening. The two big players in that range of throttle openings are the pilot jet & the pilot air screw. The pilot jets are typically are sized around, say, #30 to #60, and normally in increments of 5s. If you're having problems with the bike not running well at low throttle openings, these are the areas to focus on first. The amount of cutaway in the slide (p/n 11, called the throttle valve in your diagram) can also have an influence in the 1/8 to 1/2 opening ranges, and I mention this because between the 3 of these carb parts, you can usually fix low throttle position stumbles & bogs n the type of carb shown.

You need to have the low to mid throttle openings dialed in and running good first, because typically, this is where your throttle is at, most of the time, while trail riding, and some off-road riding. It always seems to make dialing in the mainjet/wide open throttle circuit easier with the low-throttle circuits working well first, for me anyways.....

The main jet is evaluated at the wide open throttle opening. The main jets typically have a number with the value you mentioned, like #200. but without knowing more about your bike, it's tough to say what increments the main jets come in for your bike, or what size to try, & etc..

I hope this helps a little, and doesn't sound like I'm trying to be a jerk, know-it-all, or condescending moron. I just wanna help. If possible, you can help us out by giving a little more info, Jim Bob.

Jimmie

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I think there might possibly be a little bit of confusion on what the different circuits, and their parts, get called...... It sounds like you're possibly trying to make changes to a couple of different circuits, and maybe are a little confused about which does what, what they're called, & etc.?

Like was said above, going from a #200 to a #60 main jet is a HUGE difference; one that could possibly cause some serious engine problems if the 200 main jet was reasonably close to the correct size..... Unless you plan on never opening your throttle wide open again.... :thumbsup:

First of all, what is your bike "doing" wrong that makes you feel it needs some brass swapped around, JimBob? What kinda bike is it, size, year, & etc.?

Now, if you're having problems with "barely open" throttle positions, the only air-to-fuel mixture screw that carb shows is for the slow speed/low throttle opening circuit. It basically works from idle to around 3/8 throttle opening. The two big players in that range of throttle openings are the pilot jet & the pilot air screw. The pilot jets are typically are sized around, say, #30 to #60, and normally in increments of 5s. If you're having problems with the bike not running well at low throttle openings, these are the areas to focus on first. The amount of cutaway in the slide (p/n 11, called the throttle valve in your diagram) can also have an influence in the 1/8 to 1/2 opening ranges, and I mention this because between the 3 of these carb parts, you can usually fix low throttle position stumbles & bogs n the type of carb shown.

You need to have the low to mid throttle openings dialed in and running good first, because typically, this is where your throttle is at, most of the time, while trail riding, and some off-road riding. It always seems to make dialing in the mainjet/wide open throttle circuit easier with the low-throttle circuits working well first, for me anyways.....

The main jet is evaluated at the wide open throttle opening. The main jets typically have a number with the value you mentioned, like #200. but without knowing more about your bike, it's tough to say what increments the main jets come in for your bike, or what size to try, & etc..

I hope this helps a little, and doesn't sound like I'm trying to be a jerk, know-it-all, or condescending moron. I just wanna help. If possible, you can help us out by giving a little more info, Jim Bob.

Jimmie

Hi Jimmie,

Basically I bought a 1997 KX100 2nd hand off a guy and I have hardly rode it due to other problems - oil leaks, new top end, etc.

It is still not running as I have decided to fit new clutch springs as the ones on their were about 1mm shorter than recommended. I am just awaiting delivery of them!

Anyway, the Previous Owner fitted a 2001+ (year) Carb fitted (Keihin PWK-28) but put the jets from the 1997 Carb (Keihin PE-26) into this 2001+ Carb.

The problem is that they 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 (Due to the Jets moved from the 1997 Carb):

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)

I was thinking that it would be a good idea to put the correct Jets in, as they seem wildly out when you look at the Kawasaki's standard jets which I said above.

I was thinking of purchasing all the Jets which are meant to be fitted in a 2001+ Carb and fit them into my 2001+ Carb.

I need to change the Main Air Jet if I am going to do that, but I don't know what the Main Air Jet is?!

You don't sound like a Jerk at all, I am very appreciative of the help. I am fairly new to motorbikes so I am still learning and I appreciate as much help as possible!

Thanks and ATB

James

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I have never heard of a main air jet, and the diagram you posted doesn't list one. This is what I think is causing everyone confusion here. Perhaps the Kawasaki 2t forum would be more helpful to you.

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I have never heard of a main air jet, and the diagram you posted doesn't list one. This is what I think is causing everyone confusion here. Perhaps the Kawasaki 2t forum would be more helpful to you.

I will try the Kawasaki 2T Forum, thanks for that suggestion!

Could they just be calling the Pilot Air Jet the Main Air Jet?

Thanks and ATB

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Who is they? And I have never heard of any "air jet". I have heard of air screws, which only work in tandem with the pilot jet.

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Who is they? And I have never heard of any "air jet". I have heard of air screws, which only work in tandem with the pilot jet.

The people who have written the KX100 Service Manual.

Maybe I won't change the 'Main Air Jet', and just change the Main Jet, Pilot Jet and the Jet Needle and see how it goes?!

Thanks and ATB

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Hi, James!!!

Okay, I guess we posted above here at a fairly close times, and I hadn't seen your link to that other thread. That helps a lot! (Also, I'm slow to type, so my response time is slow.... like my riding/racing..... :confused: )

Here's what ya need to do first: Get the oil leak & clutch issues sorted out first, along with anything else that may need fixing. Your motor needs to be in good mechanical condition to get the jetting to optimum, or even "just close". It's very hard to get the correct jetting with something wrong with an engine like, low compression, or a power valve not working, or whatever. Get everything else sorted out as best as you can, first.

Okay. Your PWK has several "circuits" designed into it to cover the variety of throttle openings a rider uses when out riding. One "circuit" covers small throttle openings (0/idle to 1/8 open throttle), another covers slightly bigger throttle openings (1/8 to 3/8 openings), then the next circuit will take care of, say, 3/8 to 3/4 open throttle, and finally you have a circuit to cover the wide open throttle situation, your main jet circuit. All these 'circuits' are nothing more than little holes & tunnels machined into the carb's body, with their openings controlled by the sizes of the holes in the jets, the opening controlled by the pilot air jet, screw, and the size & taper of the needle. There is some built in "overlap" of all these different circuits, so when you open up a throttle, either slowly or quickly, the engine should pick up rpm with no stumbles or stutters, and hopefully, without excessive smoke, fouling plugs, & etc.. And there are actually 1 or 2 more circuits than I just mentioned, to further confuse the issue... :thumbsup:

Anyways, you basically have only 2 different jets on your PWK Carb that you can switch around, James, plus your needle. Part number 20 is your pilot jet, and it's replaceable. It works on the small-throttle opening ranges I mentioned above. It has a big influence on idling speed, starting, and low speed throttle openings. It meters fuel at idle to almost 1/4 throttle openings, basically.

But that pilot jet has a helper of sorts, the pilot air screw (#16 in the diagram). Lightly screw the pilot air jet all the way in clockwise, until you feel it bottom out, or stops turning. Don't go gorilla on this screw; it can be messed up by tightening it too tightly. Just enough pressure to bottom it out. Then, back it out 1 & 1/2 turns, counter-clockwise, to begin with. This screw will have the effect of making your fuel-to-air mixture richer when screwed in, and leaner (allows more air to flow in with the fuel) when screwed out. Generally, your pilot air screw's "optimum range' will be from 1 turn out, to 2 turns out, if your pilot jet is correct, and other things are all functioning right. Listen to how your engine idles. Turn the pilot air screw in 1/2 turn, and listen to tell if the eingine smooths out, or slightly speeds up some. Then try screwing the screw out to 2 or 2 & 1/2 turns out (from being lightly bottomed out). Note if it makes a change in how it idles & sounds, or if it makes no change at all. If your engine requires you to have the pilot air screw out more than, say, 3 turns, you need a leaner (smaller number) pilot jet. The engine will typically have a slight miss or stumble when idling, and slowly opening the throttle up from idle to let you know that the mix is rich, and requires less fuel. A lot of smoke & spooge is normally a good indicator your engine is getting too much fuel for a given throttle range (circuit) also..... On the other hand, if your engine seems to need the pilot screw screwed in less than 1 turn to run cleanly, you probably need a bigger pilot jet. If it requires a pilot jet change, I'd recommend you only go one size up or down at a time. Ride it, and then see whether it helped or not, made it better or worse. This can be a time consuming process, but it's worth it when you get to the woods or the track, James.

I should mention that this adjusting of the pilot air screw needs to be done on a mechanically sound, warmed up engine, James

The other replaceable jet is #22, your Main Jet. It works when you have your throttle pegged open. Typically, you'll need to do the "plug chop" deal, and look at your spark plug to let you know if your main jet is correct or not. Look at your plug after riding it with the throttle wide open. In simplest terms, you want the plug's insulator to be a nice honey/tan brown color. Black & oily means you can put in one size smaller main jet, and ride it again to see how that works. If the plug looks whitish grey colored, it probably needs a bigger main jet. It's a process of trial & error here, James, to get the correct sizes of jets & needle that you would need......

After that, for medium throttle settings, you can change the clip position on your needle to make it richer or leaner, or completely change to another needle, to suit the needs of your engine.

Now, if your carburetor currently on your bike came off a KX100, the jetting that came with that carb should have been fairly close to right. I would try the exact jetting specified for that carb first, ride it & evaluate it, and then make thoughtful, methodical changes to fix whatever throttle openg range needs improvement.

I've gotta go now, but hopefully this will help some, and won't confuse. I'll try to check back in later, and hope you can get this sorted out.

Jimmie

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Hi, James!!!

Okay, I guess we posted above here at a fairly close times, and I hadn't seen your link to that other thread. That helps a lot! (Also, I'm slow to type, so my response time is slow.... like my riding/racing..... :busted: )

Here's what ya need to do first: Get the oil leak & clutch issues sorted out first, along with anything else that may need fixing. Your motor needs to be in good mechanical condition to get the jetting to optimum, or even "just close". It's very hard to get the correct jetting with something wrong with an engine like, low compression, or a power valve not working, or whatever. Get everything else sorted out as best as you can, first.

Okay. Your PWK has several "circuits" designed into it to cover the variety of throttle openings a rider uses when out riding. One "circuit" covers small throttle openings (0/idle to 1/8 open throttle), another covers slightly bigger throttle openings (1/8 to 3/8 openings), then the next circuit will take care of, say, 3/8 to 3/4 open throttle, and finally you have a circuit to cover the wide open throttle situation, your main jet circuit. All these 'circuits' are nothing more than little holes & tunnels machined into the carb's body, with their openings controlled by the sizes of the holes in the jets, the opening controlled by the pilot air jet, screw, and the size & taper of the needle. There is some built in "overlap" of all these different circuits, so when you open up a throttle, either slowly or quickly, the engine should pick up rpm with no stumbles or stutters, and hopefully, without excessive smoke, fouling plugs, & etc.. And there are actually 1 or 2 more circuits than I just mentioned, to further confuse the issue... :confused:

Anyways, you basically have only 2 different jets on your PWK Carb that you can switch around, James, plus your needle. Part number 20 is your pilot jet, and it's replaceable. It works on the small-throttle opening ranges I mentioned above. It has a big influence on idling speed, starting, and low speed throttle openings. It meters fuel at idle to almost 1/4 throttle openings, basically.

But that pilot jet has a helper of sorts, the pilot air screw (#16 in the diagram). Lightly screw the pilot air jet all the way in clockwise, until you feel it bottom out, or stops turning. Don't go gorilla on this screw; it can be messed up by tightening it too tightly. Just enough pressure to bottom it out. Then, back it out 1 & 1/2 turns, counter-clockwise, to begin with. This screw will have the effect of making your fuel-to-air mixture richer when screwed in, and leaner (allows more air to flow in with the fuel) when screwed out. Generally, your pilot air screw's "optimum range' will be from 1 turn out, to 2 turns out, if your pilot jet is correct, and other things are all functioning right. Listen to how your engine idles. Turn the pilot air screw in 1/2 turn, and listen to tell if the eingine smooths out, or slightly speeds up some. Then try screwing the screw out to 2 or 2 & 1/2 turns out (from being lightly bottomed out). Note if it makes a change in how it idles & sounds, or if it makes no change at all. If your engine requires you to have the pilot air screw out more than, say, 3 turns, you need a leaner (smaller number) pilot jet. The engine will typically have a slight miss or stumble when idling, and slowly opening the throttle up from idle to let you know that the mix is rich, and requires less fuel. A lot of smoke & spooge is normally a good indicator your engine is getting too much fuel for a given throttle range (circuit) also..... On the other hand, if your engine seems to need the pilot screw screwed in less than 1 turn to run cleanly, you probably need a bigger pilot jet. If it requires a pilot jet change, I'd recommend you only go one size up or down at a time. Ride it, and then see whether it helped or not, made it better or worse. This can be a time consuming process, but it's worth it when you get to the woods or the track, James.

I should mention that this adjusting of the pilot air screw needs to be done on a mechanically sound, warmed up engine, James

The other replaceable jet is #22, your Main Jet. It works when you have your throttle pegged open. Typically, you'll need to do the "plug chop" deal, and look at your spark plug to let you know if your main jet is correct or not. Look at your plug after riding it with the throttle wide open. In simplest terms, you want the plug's insulator to be a nice honey/tan brown color. Black & oily means you can put in one size smaller main jet, and ride it again to see how that works. If the plug looks whitish grey colored, it probably needs a bigger main jet. It's a process of trial & error here, James, to get the correct sizes of jets & needle that you would need......

After that, for medium throttle settings, you can change the clip position on your needle to make it richer or leaner, or completely change to another needle, to suit the needs of your engine.

Now, if your carburetor currently on your bike came off a KX100, the jetting that came with that carb should have been fairly close to right. I would try the exact jetting specified for that carb first, ride it & evaluate it, and then make thoughtful, methodical changes to fix whatever throttle openg range needs improvement.

I've gotta go now, but hopefully this will help some, and won't confuse. I'll try to check back in later, and hope you can get this sorted out.

Jimmie

Hi Jimmie,

Thankyou ever so much for that very detailed explanation, it certainly has helped me!

I am ordering the Jets on Tuesday (Bank Holiday Tomorrow) so I should get them soon hopefully, I will let you know how I get on though!

Thanks once again! You are a star! :worthy::thumbsup:

ATVB

James

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