Gas leaking

Joei

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Hi guys,

So I recently got a '77 XS650 and it wasn't starting so I replaced the battery it would finally started but I had to turn the throttle as I was kickstarting it. While I was turning the throttle there was also a lot of popping coming from the exhaust. When I would close the throttle it would turn off. I started to mess with the idle screw and it finally stayed on!

After driving it around the block a couple of times and seeing it would stay on, I decided I would drive it a little farther and after about 20 minutes it seemed like the RPMs at idle were going lower and lower and eventually turned off on me again. I so I just started to mess with the idle screw again and it stayed on again.

I drove it like this for another day or two and now there is gas leaking when I turn the petcock to "On". Would you guys happen to know what I would have to replace from this info? I can provide more if anything is unclear. Thanks!
 
The leaking gas issue is a stuck open float valve - probably the valve (dirt, gum), but could be the float itself. The other idle screw related issues may be general carb maladies. It's very common to have to remove and disassemble carbs on new-to-you old bikes - they likely need a good cleaning (ain't no shortcuts).
 
Ahhh okay gotcha thank you!! I saw that Team Miyagi on youtube has a video on how to disassemble the carb and clean it I will watch that one and try it out. Also by any chance would you happen to know how to tell what kind of carb you have? I saw some posts on here about how Uni Filter air filters were the best ones to use, but I'm not sure which ones to buy yet haha. When I take it apart I would like to just replace those as well.
 
Thanks a lot I appreciate it! I will try to add a picture of it right now. I can take some better ones later if its not clear in the one I already have on my phone.
 
IMG_1780.png
 
Yep, those appear to be the original '77 BS38 carbs aka "584" - as their Yamaha part numbers (whole carb) are 584-14901, 584-14902

And may I suggest that you retain the stock air filters.....unless you're planning other modifications (cosmetic & otherwise). There are threads on here somewhere regarding replacing the foam elements on stock filters - they'll be fine.
 
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For your BS38 carbs, you will want the UNI UP-4200 or UP-4200ST (dual layer). You don't want the "AST" one, it has an angled flange. This is my '78 with the UP-4200. It's all you need and cheaper than the dual layer "ST" type .....

Uni Pod.jpg
 
Yep, those appear to be the original '77 BS38 carbs aka "584" - as their Yamaha part numbers (whole carb) are 584-14901, 584-14902

And may I suggest that you retain the stock air filters.....unless you're planning other modifications (cosmetic & otherwise). There are threads on here somewhere regarding replacing the foam elements on stock filters - they'll be fine.
Thanks for all your help! Yeah the reason I was thinking of going with Uni was because I read somewhere on here that they were better. If they don't make that much of a difference I might just buy some stock filters since I have the original case for them. Although, I may not have stock filters then since the ones I have do not have an foam elements on them.
 
Show us what you have now. K&N, an aftermarket air filter company, makes nice airbox replacement elements. They work well but are quite expensive (about $80 a pair). If you have them, I'd just stick with them. Here's what they look like .....

AirboxK&Ns2.jpg


They are pleated wire mesh with surgical gauge trapped between it. Like I said, if this is what you have, they are very good and I would keep them.
 
Ohh yeah I think those are the exact ones that I have here is a picture of them. You think these are fine to keep using then?
 

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Ohh yeah I think those are the exact ones that I have here is a picture of them. You think these are fine to keep using then?
If those are K&N, you hit the jackpot. Many auto parts dealers sell the K&N recharger kit, which is soap and oil. Also, K&N will replace their filters if anything ever goes wrong with them.
 
David Vizard has a really interesting video on Youtube on why K&N filters work so well even when covered with dust.
 
Yes, keep using those, but you need to oil them. K&N makes special oil for them and, as mentioned, you can get it at most auto parts stores.
 
Yes, keep using those, but you need to oil them. K&N makes special oil for them and, as mentioned, you can get it at most auto parts stores.
Gotcha! Thanks for all the help! I will be going to the auto parts store to purchase the cleaner and oil kit later.
 
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