Carburetor Adjustment help
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Thread: Carburetor Adjustment help

  1. #1
    Member stevericotta's Avatar
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    Carburetor Adjustment help

    Good evening everyone! I'm a newbie from Burbank Ca, and I could use some help. I just bought a 1990 TW200 that was sitting for a while so I rebuilt the card, changed the oil, etc. It's in great shape but after rebuilding the Carburetor I am having some issues. So here is the skinny. I bought a carb rebuilt kit from Yamaha, as well as the diaphragm. I put the carb back on the bike, set the mixture screw 2.5 turns out (base setting I think) and started the bike with the choke on. No problem started right up but as soon as I take the choke off it dies. So long story short I have to have the mixture screw out about 5.5 turns for it to start up and idle without the choke. However once I give it gas it falls on it face. It wont die and if I feather it, it will rev up. So I spent about 2 hours trying every mixture setting and I can get it to close but there is always a flat spot and its running really lean. The plug is white.

    Sorry if this is long but I wanted to explain it best I could. I have read a lot of the posts about adding shims and jets but for now all I am trying to do is get it back to stock.

    BTW, its a CA bike so it has that can and stuff.IMG_5399.JPG

    Thanks for the help!
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  2. #2
    Senior Member SportsterDoc's Avatar
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    Check for a vacuum leak
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  3. #3
    Member stevericotta's Avatar
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    Would you know where I could look? I replaced the gas line and other than the vent tube for the canister there is nothing else.
    littletommy and Ken like this.

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  5. #4
    Senior Member elime's Avatar
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    Could be a clogged, or partially clogged pilot jet or a leaky o-ring on the idle mixture screw.
    P4080026.JPG3645d.jpgP3190024 (2).JPG
    Last edited by elime; 04-08-2017 at 10:03 PM.
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  6. #5
    Member MidnightRider's Avatar
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    It's a 90. The carb boot could be shrunk, leaking air, or have a crack somewhere.
    Last edited by MidnightRider; 04-09-2017 at 12:40 AM.
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  7. #6
    Super Moderator littletommy's Avatar
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    Welcome to the forum!!
    Quote Originally Posted by stevericotta View Post
    Good evening everyone! I'm a newbie from Burbank Ca, and I could use some help. I just bought a 1990 TW200 that was sitting for a while so I rebuilt the card, changed the oil, etc. It's in great shape but after rebuilding the Carburetor I am having some issues. So here is the skinny. I bought a carb rebuilt kit from Yamaha, as well as the diaphragm. I put the carb back on the bike, set the mixture screw 2.5 turns out (base setting I think) and started the bike with the choke on. No problem started right up but as soon as I take the choke off it dies. So long story short I have to have the mixture screw out about 5.5 turns for it to start up and idle without the choke. However once I give it gas it falls on it face. It wont die and if I feather it, it will rev up. So I spent about 2 hours trying every mixture setting and I can get it to close but there is always a flat spot and its running really lean. The plug is white.

    Sorry if this is long but I wanted to explain it best I could. I have read a lot of the posts about adding shims and jets but for now all I am trying to do is get it back to stock.

    BTW, its a CA bike so it has that can and stuff.IMG_5399.JPG

    Thanks for the help!
    Ken likes this.
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  8. #7
    Senior Member GaryL's Avatar
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    The very first place to look is in the boot between the carb and air box. If that is not a ful seal then forget about getting the carb adjusted. While it is running at idle spray some WD or carb cleaner around the boot and if the rpms go up or down you have a leak. Also check to be sure the mice have no nests in the air box behind the battery where it sucks air from. Some guys like to stuff a rag down in that section for wiping their hands not realizing this is the air intake.

    GaryL
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  9. #8
    Member stevericotta's Avatar
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    Laying in bed last night I thought the same thing! check the Manifold/boot.Great info all, thanks for the help. I will give is a look after I get back from church and send an update.
    Thanks!
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  10. #9
    Member stevericotta's Avatar
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    Looks like it is the o-ring between the boot/manifold. Ordered both just to be safe so I should be riding by the end of the week.

    Thanks for all the feedback!
    Steve

  11. #10
    Senior Member GaryL's Avatar
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    Good idea Steve. The Boot connection between the carb and the air box is famous for shrinking and becoming very hard so you can't get a good seal. The boot between the carb and the engine is know to crack and become very brittle from the heat. If either boot is leaking then it essentially throws your Air-Fuel mixture completely off so adjusting the Pilot screw is pretty much meaningless.

    GaryL
    littletommy and cowboyjeff like this.
    Since light travels faster than sound, some people appear bright until you hear them speak.
    If I agreed with you, we'd both be wrong.

    2006 TW200
    2006 XT225
    Kubota BX2370 Subcompact tractor with snow blower
    Wilderness System Ride 115 fishing Kayaks
    1974 Boston Whaler Montauk
    1989 Lowe Lunker

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