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I noticed that there appears to be a black plastic slotted screw in the side of the carb, can someone tell me what this seemingly screw shaped device is?



I'm a "new" owner of a once southern machine, (a 1987 unit that is unmolested, all stock and original), and I need to adjust the air fuel screw, which I believe is still capped from the factory. I don't think this "screw" has anything to do with the air / fuel ratio, but its job has me puzzled.



I'll post a pic with an arrow... hopefully it will show, sort of situated behind the short hose. Can someone tell me what its job is?



 

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I'm thinking you're right.



I've turned it... it doesn't thread out and it doesn't seem to thread in.



I've had carbs from older bikes, (my first was a Yamaha TY250 from 1974), apart with no issues and not seen this type of plug / screw.



Likewise, I've jetted carbs from modern day machines, (2007 and up dual sports like those found on the DRZ), and have not seen such a device.



I'm rather interested in why Yamaha put it there and why it carries a screw slot when it doesn't seem to be in a threaded hole.
 

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I know this thread has been dead for quite a while but I'm trying to source this black screw/plug and I haven't had any luck. I wasn't observant enough and tried to drill out the plug because I couldn't remove it with a screwdriver and wanted to make sure I removed all parts while cleaning and rebuilding it (thinking that I could find a replacement without a problem). Well, I destroyed the plug and now it looks like my only option is to machine a new one out of some kind of plastic which isn't that difficult. If anyone has detailed photos of one of these plugs that they could post, it would be greatly appreciated. Measurements would also help. Does anyone know if this could be replaced with just a simple rubber or plastic cylinder without the flat end piece that fits in the slot in the slide?

Thanks.

By the way, I just bought an 89 TW200 that was caked in mud, hotwired, and covered in multi-colored spraypaint. I'm in the process of restoring the entire bike to an unmolested state by completely disassembling, cleaning, servicing, and stripping the rattle-can paint using acetone and some elbow grease to reveal the original paint underneath. Progress is coming along great so far and I'll try to start a build thread at some point
 

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It is a blind plug! You don't need it because the orifice was never drilled. These carb bodies were used in other applications or sourced from them where this port might have been used. If it really bugs you just fill it with JBWeld and be done.

GaryL
 

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It is a blind plug! You don't need it because the orifice was never drilled. These carb bodies were used in other applications or sourced from them where this port might have been used. If it really bugs you just fill it with JBWeld and be done.

GaryL
On my carburetor, this port opens into the center of the carburetor and the raised flat section at the end of the plug corresponds to the slot that runs vertically along the slide. If I'm not mistaken, the absence of this plug would lead to an increase in airflow into the carburetor and would adversely affect its proper function.
 

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Let's see some pics. I bought a 1992 in the same situation except it was all black spray paint. And the owner lived on a dairy farm and worked on a hog farm. I bet I found a pound of dirt caked under the gas tank when I took it off. I only took the bigger parts of the bike off. For the smaller parts I was cleaning I used S100 and a air hose, rinse and repeat on some areas, but it worked great for getting into the little areas fingers don't.
 

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Let's see some pics. I bought a 1992 in the same situation except it was all black spray paint. And the owner lived on a dairy farm and worked on a hog farm. I bet I found a pound of dirt caked under the gas tank when I took it off. I only took the bigger parts of the bike off. For the smaller parts I was cleaning I used S100 and a air hose, rinse and repeat on some areas, but it worked great for getting into the little areas fingers don't.
Here's a shot of the engine the day I looked at the bike. Since then it's been completely disassembled. The carb was pretty dirty but after a thorough breakdown and soak in simple green, the parts cleaned up nicely.

You can see in the photo that the slide is visible through the port in the side of the carb.

IMG_3795_small.jpg IMG_3880_small.jpg IMG_3929_small.jpg IMG_3931_small.jpg
 

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On my carburetor, this port opens into the center of the carburetor and the raised flat section at the end of the plug corresponds to the slot that runs vertically along the slide. If I'm not mistaken, the absence of this plug would lead to an increase in airflow into the carburetor and would adversely affect its proper function.
You may be absolutely correct. I could not view the picture this morning on my IPad but can see it now. That plug goes through the the slide body and gives the slide a guide where the slit in the slide would align with. Keeps the slide from twisting.

GaryL
 

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You may be absolutely correct. I could not view the picture this morning on my IPad but can see it now. That plug goes through the the slide body and gives the slide a guide where the slit in the slide would align with. Keeps the slide from twisting.

GaryL
I'm getting a new one machined out of some delrin by a buddy at work (I, unfortunately, only have limited access to the machine shop at work). I'll post photos when done
 

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Good day chaps.

Could anyone please tell me where the AIR SCREW is on these older carbs, I found my TW on a dump and not sure if these carbs have a preset air screw, I have had it apart a few times but cannot find an air screw...Please help?
 

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Welcome to the forum!! The air/fuel screw is on the bottom of the carb towards the front of the carb. They come from the factory with a little cover pressed in over it, so you don't see it right away. You have to remove the cover to get to the pilot jet. You do not have to put it back on, it is there to help prevent tampering and keep the bike as lean as possible for emissions. Try about 2 and 1/2 turns out and go from there. It will help a lot with cold starts and warm up time. Let us know if you have any more questions!! You may see that the cover has a little pin hole in it. Drill it open more so you can get to it or put a sheet metal screw in it and yank it out.
 

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Good day and welcome highwayabuser! A dump find TW? Awesome potential to take it from the dust bin to a fun cruiser. Let us know how to help and post some pics if possible of your find.
 

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Good day chaps.

Could anyone please tell me where the AIR SCREW is on these older carbs, I found my TW on a dump and not sure if these carbs have a preset air screw, I have had it apart a few times but cannot find an air screw...Please help?
This is the newer CV carb. The older slide carb has the fuel/pilot screw in a similar location



jb
 

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It is a blind plug! You don't need it because the orifice was never drilled. These carb bodies were used in other applications or sourced from them where this port might have been used. If it really bugs you just fill it with JBWeld and be done.

GaryL

The only plugs I ever knew that could see were old worn out horses and some of them were blind too.
 

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Awesome guys and girls......found it !! A word of thanks to all.
I had the frame sand blasted and powder coated all the parts, including the wheels , hubs and spokes Matt black, It has taken me just three weeks to get her done. Fitted new wheel bearings, swing arm bearings new OE cables, grips the works. Took the little Yamaha with a BIG heart for a spin on Sunday and she is a fine little Meatball.Yamaha In Cape Town were brilliant at getting all the parts I needed. I will post pictures as soon as I can work out how too.

What a pleasant machine they are.
 
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