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the sticky throttle shafts are technically non-servicable. According to Yamaha, you fix this problem by replacing the carbs. Honestly, i'm surprised there hasn't been a recall on this, since they had a recall on the throttle cable thing.
Take out the carbs. Take off the linkage on the bottom of the carbs, remove the springs and arms on the bottom of the throttle shaft. Take a heat gun to the top and bottom of the throttle butterfly where the shaft goes through the carb body. Do not use a torch for this. I don't want anybody blowing their face off. There is gas in those things, a heat gun is dangerous enough. Heat up the carbs one at a time with the heat gun and manipulate the throttles individually to see which one(s) is / are binding. This will allow you to identify which ones need fixing and which ones don't.
On the carb(s) that need fixing: Grind the threaded end off the screws on the throttle butterfly, remove the screws, and carefully remove the throttle blade, noting the correct orientation. Once this has been removed the shaft should pull right out. If you don't grind off the end of the screws, you will break screws and you will have to drill them out, which means you will probably damage the throttle shaft. Don't do this. Remember, non-serviceable part. F it up, you have to buy a new carb (which is officially the only way to fix it anyway).
Take the screws to the local "good" hardware store / bolt supply store. Around here it's suburban bolt and supply. Aco, Ace, Tru Value probably won't have these. They are metric and they are tiny (3mm x 0.5mm pitch x 7mm Long Flat head) . Pick up a bunch of new ones. Twice as many as you need, in case you lose a couple or strip a couple. Make sure the new ones are as long as the old ones were before you started grinding on them.
Before reassembling the carbs, take some sandpaper and sand the throttle shafts lightly in the area where they were binding. You will be able to see marks on the throttle shaft in the correct area. Also sand the carb body where the throttle shaft runs through. Sand it down a little, sand it some more with a real fine grit so that it's not a rough surface, and test fit it. Hit it with a heat gun again and see if it still binds. If so, sand more. If not, you're ready to reassemble. Eventually, you'll be able to get it good and hot with no binding. That's when it's fixed. Don't take too much off though, you don't want any play in this area, only enough clearance for the bushing to expand with heat, without binding.
Put a good coating of grease on the throttle shaft in the areas where it goes through the carb body. Maybe put some grease in the holes in the carb body too. Put the throttle shaft back in. Make sure you don't have grease on the holes where the throttle blade screws on. Reinsert the throttle blade, making sure the holes are lined up properly and the blade is oriented correctly. Make sure the throttle operates smoothly. Install new screws, using loctite 271, the high strength red stuff. Or the permatex equivalent, permatex 27100. Make sure you have plenty on the threads, but not so much on there as to interfere with the operation of the throttle. Once the screws are in and tight, booger up the threads that are protruding through the other side. Use a screwdriver or pair of pliers to deform the threads so the screw can't back out. Be very careful not to bend the throttle blade in the process.
That's it. Now just reassemble and reinstall and you should be good to go. If you sanded enough off the throttle shaft and out of the hole in the carb body, your sticky throttle will be fixed.
No need for a machine shop, no need for any new yamaha parts. Yamaha doesn't exactly support this repair, and like I said, that throttle butterfly is not a serviceable part.
Be aware that if those screws come loose, they go in your engine. Which is why you want to loctite them and booger the threads.
Take out the carbs. Take off the linkage on the bottom of the carbs, remove the springs and arms on the bottom of the throttle shaft. Take a heat gun to the top and bottom of the throttle butterfly where the shaft goes through the carb body. Do not use a torch for this. I don't want anybody blowing their face off. There is gas in those things, a heat gun is dangerous enough. Heat up the carbs one at a time with the heat gun and manipulate the throttles individually to see which one(s) is / are binding. This will allow you to identify which ones need fixing and which ones don't.
On the carb(s) that need fixing: Grind the threaded end off the screws on the throttle butterfly, remove the screws, and carefully remove the throttle blade, noting the correct orientation. Once this has been removed the shaft should pull right out. If you don't grind off the end of the screws, you will break screws and you will have to drill them out, which means you will probably damage the throttle shaft. Don't do this. Remember, non-serviceable part. F it up, you have to buy a new carb (which is officially the only way to fix it anyway).
Take the screws to the local "good" hardware store / bolt supply store. Around here it's suburban bolt and supply. Aco, Ace, Tru Value probably won't have these. They are metric and they are tiny (3mm x 0.5mm pitch x 7mm Long Flat head) . Pick up a bunch of new ones. Twice as many as you need, in case you lose a couple or strip a couple. Make sure the new ones are as long as the old ones were before you started grinding on them.
Before reassembling the carbs, take some sandpaper and sand the throttle shafts lightly in the area where they were binding. You will be able to see marks on the throttle shaft in the correct area. Also sand the carb body where the throttle shaft runs through. Sand it down a little, sand it some more with a real fine grit so that it's not a rough surface, and test fit it. Hit it with a heat gun again and see if it still binds. If so, sand more. If not, you're ready to reassemble. Eventually, you'll be able to get it good and hot with no binding. That's when it's fixed. Don't take too much off though, you don't want any play in this area, only enough clearance for the bushing to expand with heat, without binding.
Put a good coating of grease on the throttle shaft in the areas where it goes through the carb body. Maybe put some grease in the holes in the carb body too. Put the throttle shaft back in. Make sure you don't have grease on the holes where the throttle blade screws on. Reinsert the throttle blade, making sure the holes are lined up properly and the blade is oriented correctly. Make sure the throttle operates smoothly. Install new screws, using loctite 271, the high strength red stuff. Or the permatex equivalent, permatex 27100. Make sure you have plenty on the threads, but not so much on there as to interfere with the operation of the throttle. Once the screws are in and tight, booger up the threads that are protruding through the other side. Use a screwdriver or pair of pliers to deform the threads so the screw can't back out. Be very careful not to bend the throttle blade in the process.
That's it. Now just reassemble and reinstall and you should be good to go. If you sanded enough off the throttle shaft and out of the hole in the carb body, your sticky throttle will be fixed.
No need for a machine shop, no need for any new yamaha parts. Yamaha doesn't exactly support this repair, and like I said, that throttle butterfly is not a serviceable part.
Be aware that if those screws come loose, they go in your engine. Which is why you want to loctite them and booger the threads.
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