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Discussion Starter #1
Has anyone here done them? How did it work out for you?

It seems to me the seat pan is the air scoop that sends air to the box and the snorkel in the box only restricts it but leaves a lip underneath so dirt/water won't slide down to the filter. Has anyone removed/modified this snorkel?

It seems to me if I enrich the fuel mix by removing the welch plug in the carb to access the mixture screw, modding the airbox will balance it out with more air resulting in faster fuel delivery? Then you'd want stronger spark plug?
 

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That is the theory, correct. Some say that the TW engine gets enough air and fuel (and exhaust flow) from the factory and that these mods do not help in the case of a TW enough to warrant them (other than a tad more open on the mixture screw).
 

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Discussion Starter #3
Unfortunately I've been on the forum long enough to know you're correct in peoples acceptance of TWs being a little under powered. It's nice that it doesn't get away from you easily and you can milk some performance out of it by how you ride it.....but I'm determined to get more out of it. I may have to get rid of the battery for a capacitor and metal tank for plastic while I'm at it. One mod at a time I'll get her running stronger.
 

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You won't see much change in the flow rate of air through the engine with only airbox mods. What will happen with changes to the snorkel, air filter and/or air box are changes in the head loss, or pressure drop across the assembly. This changes the pressure differential between upstream, and downstream sides of the carburetor which is of course the driving force that meters gasoline from the tank into the engine. This is why a dirty, clogged air filter messes up the air fuel ratio by increasing head loss across the filter creating a rich mix and why opening up the airbox helps compensate for reduced partial pressure of oxygen as elevation increases that also would normally result in a similar too rich fuel ratio. You want that 16:1 ratio all the time for naturally aspirated engines running non-ethanol and since we don't have fuel injection with it's mass air sensors we have to manually try to compensate for changes in elevation, air density, temperature, humidity and regulatory environment ( California wants us leaner than 16:1 , thus we cheat with the supposedly sealed up inaccessible and mandated non-adjustable mixture screw).

If you want to get the 196cc air pump to move more air and thus burn more gas making more horsepower via higher rpms then reducing flow restrictions is a proven approach. Larger valves mated to aftermarket exhaust systems can help but even with stronger valve springs to slam things shut quicker one will eventually face valve float and piston conflict. Longer duration cams don't help this either. Easier power-to-weight improvements include avoiding ethanol with it's lower energy density and reducing weight of bike,rider and carried gear. IBXR has a responsive TW with serious weight reduction coupled with 226cc and 6-speed upgrades at expense of some practicality like a starter motor, full fenders, horn, some lighting, etc...
 

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Unfortunately I've been on the forum long enough to know you're correct in peoples acceptance of TWs being a little under powered. It's nice that it doesn't get away from you easily and you can milk some performance out of it by how you ride it.....but I'm determined to get more out of it. I may have to get rid of the battery for a capacitor and metal tank for plastic while I'm at it. One mod at a time I'll get her running stronger.

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Discussion Starter #6
So more air + more fuel + larger jets + more spark + more open muffler..make woman ride trail faster?

But seriously, start with the fuel mixture screw first then every other mods would have to balance each other?
 

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Yes, but I guess what i'm saying is that for the 196cc that this engine has, it has adequate airflow in and out in stock form and is just slightly lean. You may want to increase the size of the jug and up the carburetor size a few mm to get what you want. Even porting the head has demonstrated very little improvement. A lot of bikes are "dialed back" and will have substantial gains from what you want to do, not so much in this case (IMHO). You should have gotten the engine along with the wheel and swingarm you just got. That would have given you exactly what you are looking for.


So more air + more fuel + larger jets + more spark + more open muffler..make woman ride trail faster?

But seriously, start with the fuel mixture screw first then every other mods would have to balance each other?
 

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Strive for balance Grasshopper. As Confucius once said: "It does not matter how slowly you go so long as you do not stop"
Confucius must have better balance than I do!



Tom
 

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You won't see much change in the flow rate of air through the engine with only airbox mods. What will happen with changes to the snorkel, air filter and/or air box are changes in the head loss, or pressure drop across the assembly. This changes the pressure differential between upstream, and downstream sides of the carburetor which is of course the driving force that meters gasoline from the tank into the engine. This is why a dirty, clogged air filter messes up the air fuel ratio by increasing head loss across the filter creating a rich mix and why opening up the airbox helps compensate for reduced partial pressure of oxygen as elevation increases that also would normally result in a similar too rich fuel ratio. You want that 16:1 ratio all the time for naturally aspirated engines running non-ethanol and since we don't have fuel injection with it's mass air sensors we have to manually try to compensate for changes in elevation, air density, temperature, humidity and regulatory environment ( California wants us leaner than 16:1 , thus we cheat with the supposedly sealed up inaccessible and mandated non-adjustable mixture screw).

If you want to get the 196cc air pump to move more air and thus burn more gas making more horsepower via higher rpms then reducing flow restrictions is a proven approach. Larger valves mated to aftermarket exhaust systems can help but even with stronger valve springs to slam things shut quicker one will eventually face valve float and piston conflict. Longer duration cams don't help this either. Easier power-to-weight improvements include avoiding ethanol with it's lower energy density and reducing weight of bike,rider and carried gear. IBXR has a responsive TW with serious weight reduction coupled with 226cc and 6-speed upgrades at expense of some practicality like a starter motor, full fenders, horn, some lighting, etc...
Fred always has a great way of explaining things....
 

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From what I've seen on the forum, you can spend lots of time and $ trying to get more performance out of the TW with little improvement.
Yup! As long as I have been here and as many threads I have read from guys and gals trying to milk every last pony from the tiny engines I have yet to hear of any major success.

Elime, TW Brian and a few others have gone deep into the weeds on some major changes with varying degrees of success. I go by a simple rule, For every action there is an equal and opposite reaction. Yamaha IMO milked almost every last pony from this engine so anything we can do over what Yamaha has already done is pretty much negligible. Even dropping an XT225 engine in or upgrading to the XT jug or the 6 speed tranny only actually gives a modest boost in overall power under your seat. The fancy after market exhaust pipes leads us to carb upgrades that turn into nightmares for those not real adept with carbs.

My own personal belief where gaining more noticeable power from a TW is the object would lead me to take away the exact thing that makes a TW a TW. Put skinny tires on the front and rear to reduce weight and drag. I had both 2006 TW 200 and a 2006 XT225 in my garage at the same time. The XT was much better on the pavement and even a bit better on some trails because it had skinny tires, a little more power, 6 gears and much better suspension. The TW was way better on nasty trails simply because it had the traction from the fat tires. I bet if you married an XT rear wheel and tire to a TW you would see a noticeable difference in power and performance albeit with a reduction in traction.

GaryL
 

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Discussion Starter #13 (Edited)
I actually think the TW has less traction since it spreads out it's weight on a wider foot print. While skinny tires dig and cut like an ice skate the TW drifts, and like you mentioned, absorbs horsepower. The only real advantage is it also absorbs shock to compliment the lacking suspension and won't dig itself into soft terrain like a skinny tire bike. This is what make makes it appear to have better traction in specific situations.


I suspect most people looking to gain with mods have their sights set too high which is why they're often disappointed. A number of small improvements can make a noticeable difference collectively. But I'd rather mod a stock muffler then break the bank on an aftermarket for the little bit of gain.
 

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I removed my intake baffle and readjusted the carb. It did absolutely nothing to help. Combine this with the exhaust mod and you might get something. Then there is the intake pulse debate which was posted before on the forum. Thumper Talk mentioned anything over 1 1/4 inch exhaust mod made single cylinders louder but no gain. I watched a show where a guy hooked up a motorcycle ignition on a Briggs and Stratton lawnmower and it ran fast. I have wondered if a quicker ignition system would improve it any? Possibly along with the other mods it would. I found some interesting articles on exhaust recently and the pressure and pulse information I had never heard of. I looked at so much I can't refer any. I just did lots of Google searches.
 

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Discussion Starter #15
When I was tinkering with 2 stroke motorized bicycles the biggest mods you could make were opening up the exhaust and a more powerful CDI. These two mods alone gave at least a 20% HP increase. I can only image the complication valves creates.
 

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When I was tinkering with 2 stroke motorized bicycles the biggest mods you could make were opening up the exhaust and a more powerful CDI. These two mods alone gave at least a 20% HP increase. I can only image the complication valves creates.
Back in the two stroke dirt bike days a tuned expansion chamber pipe made a big difference. With these four stroke bikes there has to be a balance between intake volume and back pressure in the exhaust system. I have no idea what the correct pressure is or how it would even be determined but I do know the closer to the correct balance you have the better it is for the engine and power band. I would not personally mess around on either side of the equation which is the top end of the engine and just figure the designers at Yamaha know best. I suppose better non ethanol fuel in conjunction with a finely tuned carb and maybe a stronger CDI and better spark plug might yield the most noticeable power increase. Changing to an aftermarket exhaust is likely more trouble and money than it is worth.

GaryL
 

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Backpressure is a myth. It's more about maintaining escape velocity to scavenge every possible bit of the spent exhaust gasses out of the cylinder before the exhaust valve slams shut, so the next fresh air+fuel charge isn't displaced by any volume of gasses you can't burn.

Smaller exhaust increases velocity and pressure, larger decreases pressure and velocity. Ideally you want low pressure and high velocity, so we're stuck with trying to find that sweet spot in the middle in regards to exhaust tubing diameter and length. It's easier to suss out in a single cylinder application like ours as you don't have to consider pressure waves from other cylinders in the same path, but I don't think there is really a tried and true "easy" formula out there.

In the absence of CFD software and a decent engine model to load into it, the mass of air plus the mass of fuel should be equivalent to the mass of exhaust for a given cycle, but factors like intake restriction, ability of the carb to supply fuel, valve sizes, cam timing and duration, etc.. all make trying to TLAR it out near impossible for mere mortals.

Unless you're going to address the full system from air filter to spark arrestor, the stock exhaust is probably just fine. If anything, removing restrictions on the intake side will be more likely to yield positive results.
 

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Trail Woman, you mention turning the mixture screw. I believe (Please correct me if I am mistaken) that only affects the idle mixture and possibly transition.
Actually Smitty that adjustment plays a big roll throughout the entire acceleration spectrum. My first TW had a bit of a buck like a miss when cruising along at a steady 45-50 and it was real hard starting. Once I turned the pilot out to the 2.25- 2.50 setting that all went away and it ran nice and started easy. I consider it the Air to Fuel mixture adjustment and you can lean the mix out or richen it so your plug ceramic gets the nice tan color I like to see.

GaryL
 

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Backpressure is a myth. It's more about maintaining escape velocity to scavenge every possible bit of the spent exhaust gases out of the cylinder before the exhaust valve slams shut, so the next fresh air+fuel charge isn't displaced by any volume of gasses you can't burn.

Smaller exhaust increases velocity and pressure, larger decreases pressure and velocity. Ideally you want low pressure and high velocity, so we're stuck with trying to find that sweet spot in the middle in regards to exhaust tubing diameter and length. It's easier to suss out in a single cylinder application like ours as you don't have to consider pressure waves from other cylinders in the same path, but I don't think there is really a tried and true "easy" formula out there.

In the absence of CFD software and a decent engine model to load into it, the mass of air plus the mass of fuel should be equivalent to the mass of exhaust for a given cycle, but factors like intake restriction, ability of the carb to supply fuel, valve sizes, cam timing and duration, etc.. all make trying to TLAR it out near impossible for mere mortals.

Unless you're going to address the full system from air filter to spark arrestor, the stock exhaust is probably just fine. If anything, removing restrictions on the intake side will be more likely to yield positive results.
I am rather Mythological by nature! Back pressure may be a wrong terminology however what I was attempting to explain is there needs to be some degree of balance between the air flowing in and the exhaust flowing out. Simply bolting up a larger and less restrictive muffler won't get you much if you don't tune the intake air flow to accommodate it. I see a lot of Harley guys dump the stock mufflers and go with straight pipes. IMO that makes a lot more noise but I kind of doubt it does much for the power and engine longevity. I bet there are at least 50 different threads here from guys who upgraded to the FMF exhaust pipes and a very few got them dialed in just right and even fewer made any claims of great performance increases. Drilling out the spark arrest screen is never a good idea if you plan to ride on dry timber roads or in any parks.

GaryL
 
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