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Discussion Starter #1
i bought a 1987 tw200 yesterday, got it home and rode it around for about 10 minutes or so. After 10 minutes the damn thing started to backfire on me so i rode it home and it died as i pulled in the clutch in the driveway. i should say first that it wouldnt stay running without the choke on, so i rode it around with the choke on. i got home and inspected everything. the gas tank was pretty rusty, so i cleaned that out. i cleaned the carb and nothing was clogged up. but, as i was sitting scratching my head i discovered a missing screw that i suspect vibrated out when i was riding which is when it began to backfire. its number 30 and 31 in the picture. i have no ideaq what it is or what it is for. any help would be awesome!

thanks, Nick
 

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It's a plug and and gasket. It's cheaper to drill two straight holes that intersect and plug one than to drill a curved hole. If you were riding with the choke on, the screw was probably loose and allowing a vacuum leak. When it fell out, the leak got worse.
 

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Discussion Starter #4
It's a plug and and gasket. It's cheaper to drill two straight holes that intersect and plug one than to drill a curved hole. If you were riding with the choke on, the screw was probably loose and allowing a vacuum leak. When it fell out, the leak got worse.
what do you mean when you say to drill two straight holes that intersect and then plug one. and why would the put a screw right there if it was meant to be closed off?haha
 

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When a curved passage is needed, make it with intersecting straight holes. It is easy to drill straight holes. Very intricate routes can be developed by drilling intersecting straight holes and plugging the ends of the holes that you don't want fluid to flow through, allowing fluid to flow from from the end of one hole to its intersection with a second hole to the second hole's intersection with a third hole, then the fluid escapes out of the end of the third hole. You could actually drill an S-shaped hole, but the machinery to do so is very expensive, so curved passages are made with intersecting straight holes.
 

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The screw and gasket are used as a plug. Put it back on tight. Do not adjust, just make sure it is tight and that it stays tight.





Imagine drilling an "X" in a piece of aluminum.

An X is a combination of a left ">" and a right "<".

Only wanting the fluid to flow in the left ">" part of the X, you would drill two long holes that cross each other to create the X.

To prevent fluid from flowing through the right "<" you'd put a plug in each leg of the right "<".

The result would be a ">".

Clear as mud?
 

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Discussion Starter #9
kind of. i just dont get why they would put a hole there in the first place if it is meant to be plugged. because there is only 1 hole and its on the left side.
 

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The screw and gasket are used as a plug. Put it back on tight. Do not adjust, just make sure it is tight and that it stays tight.





Imagine drilling an "X" in a piece of aluminum.

An X is a combination of a left ">" and a right "<".

Only wanting the fluid to flow in the left ">" part of the X, you would drill two long holes that cross each other to create the X.

To prevent fluid from flowing through the right "<" you'd put a plug in each leg of the right "<".

The result would be a ">".

Clear as mud?




Makes sense to me.
 

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kind of. i just dont get why they would put a hole there in the first place if it is meant to be plugged. because there is only 1 hole and its on the left side.


Imagine you could only drill the above example from the right side. How do you drill the left ">" holes if the only access is from the right? You drill an X, then plug the right side "<" holes.
 

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Actually, to make a < passage, it is not necessary to use plugs. Just drill each hole to the point of intersect or slightly beyond, and don't drill all the way through. Now, if you need a Z or N shaped passage, you'd need to use at least one plug, assuming you have adequate access to the appropriate surfaces for drilling. One thing is certain, it's really expensive to drill ( and S shaped holes.



The screw in question is a plug. Nothing more. Dab a bit of threadlocker on it and reinstall.
 

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Actually, to make a < passage, it is not necessary to use plugs. Just drill each hole to the point of intersect or slightly beyond, and don't drill all the way through. Now, if you need a Z or N shaped passage, you'd need to use at least one plug, assuming you have adequate access to the appropriate surfaces for drilling. One thing is certain, it's really expensive to drill ( and S shaped holes.



The screw in question is a plug. Nothing more. Dab a bit of threadlocker on it and reinstall.


I forgot to add the last constraint, which I did in the post immediately above yours.
 

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Discussion Starter #14
ok, so i just need to reinstall that plug and the vaccum leak should be solved it that is truly the issue?
 

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Discussion Starter #18
wow! it runs like a dream. the only thing that sucks is it is so low geared and the top speed its happy at it about 45-50
 
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