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Discussion Starter #1
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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Check for a vacuum leak
 
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Welcome to the forum!! :D
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. View attachment 93649

Thanks for the help!
 
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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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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
 

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Discussion Starter #11
I'm back with another question/confirmation. So did the o-ring and boot and it's a lot better. The only issue I have and I think its me is when I hit the throttle hard (no load on the bike) to rev it up is falls flat for a second. I think its me because I am used to a bigger bike.

Also I am about 6 turns out on the mixture screw. I live in Burbank Ca which is about 700' above sea level. Does that sound right to you guys? Here is a picture of the plug. What do you guys think? TWplug 2.JPG
 

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6 turns out is too much. I'm surprised the screw hasn't fallen out.

Somethine is still wrong.

jb
 

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Discussion Starter #13
I hate to say it but that's what I think. Any ideas? I sprayed around the boot again to make sure there wasn't another leak and it was fine. Carb has been rebuilt will all start brand new parts. Any help would be great.

Thanks!
 

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And if you dial it to 2 1/2, what happens?
 

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Discussion Starter #15
It wont run unless I have the choke open.

One thing I did notice is on the right side (sitting on the bike) there is a black plug that turns but does move (it takes a flat head screw driver). Looks like the guy I got if from chewed it up. Not sure what that is. Anyone?
 

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Discussion Starter #16
Okay so I just popped out that black mangled piece of plastic and it was for the guild for the carb ""piston" so it doesn't turn when opening the throttle. Could that do it? Is air getting that little slide or is maybe the piston turning ever so slightly when I twist the throttle?
 

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We have heard this more than once. That black plug is the piston slide guide that goes through the barrel and should "NEVER" be messed with. I don't know if it can be replaced and I also don't know if this could be causing your issue. The slide must remain aligned inside the barrel so without the guide pin all bets are completely off. You mention the pilot screw is now at 6 turns out. Lets be sure you are counting correctly. The screw has a straight slot so one turn should be two complete revolutions of the slot with each revolution being a half turn. If you are counting just half turns then 5 half turns is where you should start. On a clock face if you turn it from the 3 to the 9 that is a half turn, turn it again around to the 3 and that is one full turn out. Most TWs run pretty good at between 2 1/2 -3 complete turns. In my opinion your spark plug color looks a bit lean to me.

GaryL
 

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Discussion Starter #18
Thanks for the feedback. It looks like from all the research I did last night that plug cannot be replaced. I will try and find a carb on eBay and go from there. Also thanks for the clarification on the turns. Looks like I have been doing it right.

Thanks!
Steve
 

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What size pilot get are you using? If the needle is 6 turns out then I bet you need a larger pilot jet.
 

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Discussion Starter #20
I can look when I get home but its what comes with the rebuild kit. Also I found a carb for a 1991 on ebay buts its not a california model. Will that work for my bike?

Thanks!
Steve
 
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