The Yamaha TW200 Thread...

Discussion in 'Thumpers' started by neepuk, Jan 10, 2009.

  1. Snapper33

    Snapper33 Globetrotter Supporter

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    I searched here and on TW200 forum for Carburetor Vent mod; for water crossing. On the TW200 forum, there are threads, but the photos are gone. Does anyone here have photos and a writeup to share? There is also some discussion on the seat foam for intake snorkel. What does this forum of experts know?
  2. Randy

    Randy Long timer

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    No photos to share, but it's a pretty simple idea. The float bowl needs to be vented to atmosphere. The vent line typically runs down and terminates somewhere below the swing arm pivot area. In deep water crossing this location can be below the waterline, blocking the vent and creating bogging/stalling issues. The idea is to cut this tube just below the float bowl, then install a "T" fitting between the bowl and the end in it's normal location. This allows the bowl overflow to work as designed (needed if your float needle ever gets crud in it, or whatever... You want the excess fuel to drain down below the bike in a safe location rather than pouring into the cylinder or dribbling all over the bike elsewhere so the stock vent hose still needs to terminate in the usual location). But, then, to prevent the water crossing issue, put a second length of tubing on the "T" that you installed, and run it up to a higher location. Usually somewhere up under the tank near the steering head. When done in this way, the overflow function still works, AND, even if the lower hose is blocked, the float bowl is still vented to atmosphere so the bike continues to run normally.
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  3. Randy

    Randy Long timer

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    Rereading that, I'm not sure how clear my description is... Sometimes a picture is worth a thousand words... Or in this case, maybe a simple diagram...


    [​IMG]


    As you can see, the original tube, terminating in original location, still serves as a carb overflow drain, and the newly installed tube provides venting in the event the original is temporarily obstructed during a high water crossing.
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  4. Randy

    Randy Long timer

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    And, because this is the internet, and shit tends to happen, let me make one more comment on this subject...

    While I'm sure that most here are fully aware of what I'm about to say, I also realize that some may not be... There could be someone that comes along, reads the above and says, "Why bother with the "T"? I'll just stick on a longer tube and run it up high..."

    And yep, that would work... Until you had a float needle stick and not shut off the fuel supply to the float bowl... Think about it... Liquids don't like flowing uphill. The tank is the highest point in the system. Liquids like flowing downhill. The float needle keeps this in check. As long as it functions properly. If the float needle valve seal fails to do what it does, fuel continues to flow into the float bowl until the bowl is full... Then, it has to go somewhere, because the fuel tank is still higher and pushing fuel with head pressure. Normally, it flows out the bowl overflow tube, then down the rubber tube to dribble on the ground below the bike. BUT, if you reroute that rubber tube higher than the bowl, where does the fuel go? It'll continue to rise until it flows up the jets and into the venturi. From there it'll flow into the airbox and/or the intake, potentially filling the crankcase with gasoline.

    Leave the lower vent/drain tube intact though, and the fuel has an out... It'll simply flow out the overflow tube and down to beneath the bike.

    So, in a nutshell, add the "T" and extra vent if you feel the need. But avoid the temptation of just routing the single tube higher than the float bowl...

    Another simple diagram to illustrate what I mean...


    [​IMG]
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  5. Snapper33

    Snapper33 Globetrotter Supporter

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    Randy, Thank you! Your description and write up is clear as a bell.
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  6. mikeped

    mikeped Adventurer

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    Most people put a sintered bronze filter or aquarium stone on the upper tube end. Also consider using a street (Y) fitting instead of a T fitting. Less likely to form a liquid pocket.
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  7. Snapper33

    Snapper33 Globetrotter Supporter

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    Mikeped, great info. I’ll incorporate those recommendations.
  8. frog13

    frog13 Long timer

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    Randy & Mikeped.......great info......glad your both here. Any more tech thoughts , keepim coming.
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  9. molochnik

    molochnik Anhedonic Enthusiast

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    Not for nuthin' , but I was gonna be one of those big mouths. My kibitzing has a twist though; I ran my vent line up around my tank cushion on the RH side then looped it around to a "crankcase filter" that sits just higher than the carb.
    My reasoning was that I shouldn't have a liquid lock as the fuel can run back into the float bowl and/or the overflow...or the fuel can run out of the filter.
    I found out about troubles with a low-hanging vent on my DR in the Mojave River.
    Since I altered how the vent line runs on my DR, I've also had much less trouble getting the bike started after falling over.
    However, one can't go wrong with the method outlined above.
  10. NJ-Brett

    NJ-Brett Brett

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    I think the other posts about this are wrong.
    Its got nothing to do the the float bowl or its vent.
    Its the vent for the vacuum operated slide.
    Here is a picture of how I fixed my bike:
    [​IMG]

    The stock hose comes out to the right of the choke knob and runs under the engine.
    I added a T and ran another hose up under the gas tank.
    If I go through deep water, water will drain right out of the hose.
    Without the added hose, the water in the hose prevents the slide from responding to vacuum.
    It may be closed when you have the butterfly throttle (cable controlled) open causing a very rich condition.

    Why not run the hose up under the gas tank and not have to add anything?
    If anything gets into the hose, it will only run into the carb, not out the bottom.

    The above worked for me, I have been up to the seat in water without a problem.



  11. offroadtoys

    offroadtoys Been here awhile Supporter

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    You have the new style cv carb. On 2000 and prior it is the float bowl vents that get routed with a T. Previous descriptions were accurate.
  12. JagLite

    JagLite Long timer Supporter

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    I bought another TW today!

    upload_2019-11-9_20-46-3.png

    I have a watch on CL for TW's in Arizona where my brother moved to this past summer when he retired.
    He likes riding my TW more than my other bikes so I talked with him about getting a couple TW's down there and I can visit him in the winter so we can go exploring.
    I saw this one on CL and he contacted the owner and made arrangements to check it out today.

    He called to tell me that I bought it and that it is like new.
    2007 completely stock with very low miles.
    $2,300.

    Unfortunately I don't know when I can go down to AZ or even if I will be able to before it gets too hot...

    He will ride it for me in the meantime...
  13. molochnik

    molochnik Anhedonic Enthusiast

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    Congrats my friend! I’ve been recommending one to young guy for his first bike.
    I wish I hadn’t waited so long myself
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  14. NJ-Brett

    NJ-Brett Brett

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    I never heard of an issue with the vent on manual slide carbs.
    I have had many bikes and do not think I ever had an issue with that, 2 and 4 stokes.
    I had an old XT200 a few years ago that I flooded out a number of times and only had problems when the carb was well under water!


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  15. offroadtoys

    offroadtoys Been here awhile Supporter

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    I’ve never actually had an issue either. I just figured while I was I there rejetting and replacing lines anyway it was a good time. I don’t spend a lot of time in the water anyway but I liked the idea of raising the vent point a little higher.
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  16. offroadtoys

    offroadtoys Been here awhile Supporter

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    I don’t think any of these mods are absolutely required. The bike can be plenty enjoyed completely stock. BUT, like anyone else, I enjoy tinkering anyway
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  17. JagLite

    JagLite Long timer Supporter

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    It is very hard for me to NOT modify my bikes.
    I have never had a bike I didn't personalize to work better for me and usually I do all kinds of things.
    Necessary? Nope, just to make it a little better in one way or another.
    I'm already planning a Seat Concepts new seat, a jet kit from ProCycle, bar risers, and a Shinko 244 front tire.
    For a bike I won't get to ride for months.

    When I rent a bike I think while riding it of what changes I would do if it was mine....
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  18. Aguaski

    Aguaski Been here awhile

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    This. Sometimes I wish I could mod less and enjoy stock more, but that has proven futile.
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  19. NJ-Brett

    NJ-Brett Brett

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    Well, I do not want the bike to run like crap (or not run at all) if I go through some water.

    I got 50 miles in today, was glorious, 50F and dry.
    [​IMG]

    I followed this old firebreak for quite a while, going around down trees:
    [​IMG]

    There was a large area just before this that was quite open and I had fun chasing deer across the forest floor.
    They won as they can jump over downed trees and I have to go around.
    A very nice 50 miles.
    about 6 horseback riders, a few groups of 4 wheel drive vehicles and quite a few hikers with dogs on the main roads.

    No deep water this ride...
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  20. Snapper33

    Snapper33 Globetrotter Supporter

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    Thanks for this clarification. My TW is a 2017, so I’ll adjust to this photo and description.