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Discussion Starter #1
Hey guys,

As some of you probably know my old discussion on the "starting issue" I was very careful when reading top speed, acceleration etc
My top speed without pushing the bike to a "death" is always around 120 kmh, always on the same road, completely flat, very few cars

Now I swapped exhaust
Actually this was a bit of a project between me and my dad
We took a KTM trial exhaust, cuttred about 40cm of that, with the opportune modifications inside (shortening all the components, reading, testing bla bla bla)
I noticed few things
The exhaust clearly is way bigger, I have a very deep noise, very cool to hear, the acceleration somewhat improved a bit, the 2nd and 3rd gear when I accelerate I can feel that the bike is pushing more, not like cutting off seconds as a supercar, but definetely I can feel the bike pulling my arms
The only downside is that I lost a lot of top speed
before I reached stable 120 before releasing the throttle, now with maxed out throttle I can barely reach 105, and the bike seems that won't go over that

I am reading online that at this point the bike is probably running VERY lean because the exhaust is way bigger than the original
I should set again the mix fuel air screw? let's say I have now 3,25 (keihin carby) I should go like 1 or 2 turns out more?

I don't want to rejet the carb so please exclude this option, maybe in the future or if I can find another TW the same as mine 1993 and I will modify that one, but I want my engine and carby as stock as possible, the exhaust is the only real modification which of course is just a swap, I can remove the new and "plug" again the previous one
 

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PHP:
Not sure you have a valid option other than rejetting the carb. Your bigger exhaust is allowing more air/fuel out but you have not set up the carb to allow more air/fuel in. Exhaust changes and jetting go hand in hand and both are required to get optimal effects.

If you think of the engine as a pump you had a pump with a garden house for the intake and a garden hose for the output so you had great pressure and balanced in/out. Leaving that garden hose input and adding a 2” output means you will not be pumping enough to get the same output pressure because your input is now restricted compared to output.

Jetting is simple and not a permanent change.
 

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Now you’ve done it – you just have to keep trying for that little bit “extra” – lol

Well – the simple fix is to put the original exhaust back on, which personally I would recommend

The hard way – is to “re-jet” the carb – this means changing the main jet, not the pilot jet. Once you turn the throttle above 25% to 30%, it’s the main jet that comes into action, not the pilot we were faffing about with earlier – so turning that pilot jet out a few turns more is not going to help you

You are facing two further complications here (doing it the hard way), the first is that not all jet sizes are created equal. What one manufacturer says is 130 (for instance), is not going to match another manufacturers 130. Yes, “it should” – but “no, it won’t” – we know this from experience

The second issue is that you have a Keihin carb – superior in many ways, but the knowledge of this board doesn’t cover the Keihin carb. So you have an “odd-ball” carb” – together with the potential for someone supplying the parts for the wrong carb, compounded by the potential for differences in jet sizes for the same size from different manufacturers. All of these things have happened in the past, and will happen in the future – too many “variables”

Don’t get me wrong, I think the Keihin carb is great, I have one on my ’98 – but it’s best not messed with as there’s little information out there on just how to do it, and where to find genuine Keihin carb jets, rather than an “after-market” part that will just confuse things even more.

Sometimes, you are better off settling for what “works”, rather than searching for Unicorn droppings in the woods by candle light. My prediction, is that if you pursue this course, you will spend the next six months trying to find the solution, and more than that in in the “parts that didn’t work” bin.

As you have discovered, there are gains in certain gears, but losses in top speed – and it will always be that way until you modify that exhaust to the point where it most resembles the original TW exhaust, and end up back where you started with close to the original jet

It’s either that, or the “DG” exhaust, with the TK carb – but again, you’ll be disappointed with performance …..
 

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Discussion Starter #7
Now you’ve done it – you just have to keep trying for that little bit “extra” – lol

Well – the simple fix is to put the original exhaust back on, which personally I would recommend

The hard way – is to “re-jet” the carb – this means changing the main jet, not the pilot jet. Once you turn the throttle above 25% to 30%, it’s the main jet that comes into action, not the pilot we were faffing about with earlier – so turning that pilot jet out a few turns more is not going to help you

You are facing two further complications here (doing it the hard way), the first is that not all jet sizes are created equal. What one manufacturer says is 130 (for instance), is not going to match another manufacturers 130. Yes, “it should” – but “no, it won’t” – we know this from experience

The second issue is that you have a Keihin carb – superior in many ways, but the knowledge of this board doesn’t cover the Keihin carb. So you have an “odd-ball” carb” – together with the potential for someone supplying the parts for the wrong carb, compounded by the potential for differences in jet sizes for the same size from different manufacturers. All of these things have happened in the past, and will happen in the future – too many “variables”

Don’t get me wrong, I think the Keihin carb is great, I have one on my ’98 – but it’s best not messed with as there’s little information out there on just how to do it, and where to find genuine Keihin carb jets, rather than an “after-market” part that will just confuse things even more.

Sometimes, you are better off settling for what “works”, rather than searching for Unicorn droppings in the woods by candle light. My prediction, is that if you pursue this course, you will spend the next six months trying to find the solution, and more than that in in the “parts that didn’t work” bin.

As you have discovered, there are gains in certain gears, but losses in top speed – and it will always be that way until you modify that exhaust to the point where it most resembles the original TW exhaust, and end up back where you started with close to the original jet

It’s either that, or the “DG” exhaust, with the TK carb – but again, you’ll be disappointed with performance …..
But let's say I would like to try right?
Which jets I have to purchase and how do I change them without dismounting the whole carby?
 

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Discussion Starter #9
I'll try and trace the info tomorrow - this is going to get "complicated" ....
I called a friend of mine (ex KTM driver and seller, regional champion) he asked which cabry I have, I said Keihin, he said, no worries I have jets for it
Just let me know the measure of the stock keihin if you can Purple, so I can give him the right measure and he will improve adding a bigger one :)
 

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PHP:
Not sure you have a valid option other than rejetting the carb. Your bigger exhaust is allowing more air/fuel out but you have not set up the carb to allow more air/fuel in. Exhaust changes and jetting go hand in hand and both are required to get optimal effects.

If you think of the engine as a pump you had a pump with a garden house for the intake and a garden hose for the output so you had great pressure and balanced in/out. Leaving that garden hose input and adding a 2” output means you will not be pumping enough to get the same output pressure because your input is now restricted compared to output.

Jetting is simple and not a permanent change.
That’s a great example. Lots of engineering goes into exhausts, even though it’s such a simple principle. That’s why the good ones are expensive. I think Yamaha gave us a pretty good stocker.

jannaruto - I admire your attempt to wring as much as you can out of your bike.

And I admire all the guys on here pointing him in the right direction.
 

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There are already links on how to not have to remove the carb. Basically loosen the mounting ring and spin it to where you can remove the float bowl screws. This may require you to remove any cables, hoses which prevent it from turning. It may be easier to remove the tank also. The size of jets is partly dependent on the year also. I have a cheating method. Before I actually change jets I would run it down the road at max speed and start pulling the choke out a little at a time and see if it accelerates more. If it does speed up then a bigger jet is your answer. If it doesn't I would put the old muffler back on. I have heard it is only good to increase about 1 jet size at a time. You may have to buy several to see which one works best.
 

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Discussion Starter #12
Also another thing, for the idle mix screw, how many more turns out I should go? I mean for the low end throttle, I guess you should give a bit more turba out right? How many?
 

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OK – let the fun begin ……

Your main jet is in the centre of the carb, and works when you twist the throttle, which lifts the needle – which allows the petrol to flow. The more you twist the throttle, the higher the needle lifts, exposing more of the hole, so more petrol comes through

To get at the main jet, you need to remove the float bowl and maybe the float assembly, and look for the brass bit with a hole in it that the needle fits into. On a Keihin Carb, the main jet has a flat head slot, just make sure you have a big screwdriver

Your first possible problem is removing the float bowl (the bottom of the carb), which typically has four cross head screws, one in each corner. The issue here is that the carb is made out of a soft alloy, but so are the screws, and getting them to come out can be tricky. If you are lucky enough to succeed, do not use the same screws a second time, so have your replacements ready. You’ll likely be doing this several times, so better to play it safe

The second thing you need to be ready for, is the float bowl gasket. Again, have a spare standing by, and use it the first time the carb is taken apart. Petrol is thin stuff, and will find its way through an old gasket. With a fresh gasket, you can probably get away with it a few times, but chuck the older one in the bin the first time.

At this point, you will be able to see the bits and pieces that make your carb work, and the first thing you’ll notice is that they are (mostly) very fragile. Do not bend or force anything, or you’ll be in trouble. The first time is always the hardest, so take your time. If you can, get your racing friend to do this in front of you the first time to show you, then it will all make sense when you do it yourself the second time.

When you get the main jet out and hold it, you’ll be able to read the small lettering stamped on it. If the main jet has a sort of star shaped K it is a Keihin. There should also be three numbers showing, 116 or 118 (something in that range anyway). The bigger the number on the replacement jet, the bigger the hole, so take a note of your starting point, and try a jet with a bigger number. Take it up slowly, too big a difference will just choke the engine response.

The biggest unknown at this point, is what make of jets your friend has to offer. A square sign with a 1/4 square down in the corner of the larger square means it is a Mikuni and may not fit. The thread may be different, or the length, so examine the original next to the replacement very carefully beforehand.

Another potential problem (I told you this was going to get complicated), is that the profile of the slide needle has to seat into the jet just right, or this is going to get “erratic”. So when you are inspecting both the original jet side by side with the replacement jet, make sure that they both have the same profile to greet the needle.

This is going to involve a lot of trial and error, so ride, rinse and repeat, until you either get it right or give up – lol

I’m going to leave you with a link to think about - https://www.6sigmajetkit.com/yamaha-tw-200-trail-way-jet-kit.htm

The problem with what you are attempting, either by doing it yourself, or by simply ordering a kit from 6 sigma, is that there are so many “variables” to choose from, each one with its own difficulties

Still – if you have to have a hobby, I suppose you could do worse ……
 

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Also another thing, for the idle mix screw, how many more turns out I should go? I mean for the low end throttle, I guess you should give a bit more turba out right? How many?
Leave it as it is until you sort out the main jet
 

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Discussion Starter #15
Leave it as it is until you sort out the main jet
I will go to this friend of mine in about 2-3 weeks, that's why I am asking now for the idle screw XD
his officine is a bit far so I don't go all the time
Also he is very well prepared on these kind of stuffs, he prepare motorbikes for racing, he used to be a racer with plenty of knowledge on all bikes part, also he has a TW in his own officine that someone want him to repair (the owner did something really bad to the engine)
I am confident he can solve everything in few hours, his words: come here and we change the jets, then you will enjoy the bike again
 

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As before, moving the idle jet around will not affect your top speed, but feel free to experiment

As to you friend – sounds like a useful man to know ….. ;)
 

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Discussion Starter #17
As before, moving the idle jet around will not affect your top speed, but feel free to experiment

As to you friend – sounds like a useful man to know …..
I know another like him
Both super experienced with bikes and they do these kind of stuffs for living
The one I am going for jets was a pilot, regional champion thst eaced even outside italy for KTM, testing bikes etc
Biggest KTM shop in south italy, now he train young guys, and he appears to be specifically a suspension preparator, infact he refilled my original back suspension adding a valve, refillingnwith oil and N2O to easy maintenance in the future, bilke comoletely changing suspension feeling, he also did my front one and from him I purchased a KTM exhaust because I wanted to experiment with dad, now the acceleration is way better, in fact I feel just a little my forearma sore, not used to that "pull" and in a couple of weeks we will change jets, he will take care of that so I am already kinda sure he knows which size to put, how to correctly dismount and set everything correctly
 

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Jannaruto just as a comparison my newer TWs 2014 I bought used with DG exhausts had bad jetting. The owners changed the exhaust and had trouble rejetting them, �� why I got them cheap. I went up two sizes of main jets from a California lean stock jet of 126 and ended up with 130 main jet. Your jet sizes will be different. I also lifted up the needle by adding washers under the nylon spacer. I added two to three .02 “ washers as spacers. The washers dramatically increased the midrange acceleration.

Read these threads carefully:

http://tw200forum.com/forum/technical-write-ups/591-carb-tuning.html

On this scroll down and read Lizrdbreths carb tuning tips.

http://tw200forum.com/forum/technical-help/5751-paper-clip-my-93-carb.html

Also do a search on lifting the carb needle.

Have fun tuning

The screws on the float bowl are sometimes very tight and hard to remove they are also JIS screws and need a JIS screw driver. Many replace the bowl screws with SS Allen head or socket heat screws as Purple points out. It is east to change jets after you learn how to do it. On my bikes because the handle bars atre raised I need to remove the throttle cables from the carb before turning the carb clockwise to access the bottom and top of the carb.
 

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Discussion Starter #19
Jannaruto just as a comparison my newer TWs 2014 I bought used with DG exhausts had bad jetting. The owners changed the exhaust and had trouble rejetting them, �� why I got them cheap. I went up two sizes of main jets from a California lean stock jet of 126 and ended up with 130 main jet. Your jet sizes will be different. I also lifted up the needle by adding washers under the nylon spacer. I added two to three .02 “ washers as spacers. The washers dramatically increased the midrange acceleration.

Read these threads carefully:

http://tw200forum.com/forum/technical-write-ups/591-carb-tuning.html

On this scroll down and read Lizrdbreths carb tuning tips.

http://tw200forum.com/forum/technical-help/5751-paper-clip-my-93-carb.html

Also do a search on lifting the carb needle.

Have fun tuning

The screws on the float bowl are sometimes very tight and hard to remove they are also JIS screws and need a JIS screw driver. Many replace the bowl screws with SS Allen head or socket heat screws as Purple points out. It is east to change jets after you learn how to do it. On my bikes because the handle bars atre raised I need to remove the throttle cables from the carb before turning the carb clockwise to access the bottom and top of the carb.

I will discuss these stuffs with him but I assume he already know the needles thing, jets etc :D its his job preparing competition bikes
 

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Some carbs have grooves on the needle to change the needle height with a circlip, but our carbs have a plastic spacer so to lift the needle you add small washers between the spacer and the circlip on the needle.
 
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