I've got a 1978 Yamaha XS650 I just rebuilt. It runs nice at everything but full throttle, where it seems to start missing or stumbling. Backing off even slightly stops the stumble.
I have the timing and advance set up per the factory manual, and the advance looks like it's working correctly. Points are clean and not pitted, and properly gapped. New plugs.
I did not open the carbs during the rebuild. The bike averages around 50 MPG on my commute to work.
Any suggestions?
2007-08-28
05:19:44
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9 answers
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asked by
Chuck K
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in
Cars & Transportation
➔ Motorcycles
Well, this afternoon, while riding home from work, I met up with my daughter to ride the rest of the way home. She's got a Yamaha 400, I think an '83.
It was stumbling all the way back up to the last stop sign. I got on it hard there, and something "popped" in the carb, I guess - no more stumble - just smooth power to redline.
I figure that the carbs sitting in the garage for two years before I got around to putting it all back together might have resulted in some insects living in there - and they finally got squashed or blown out.
It's going to pour tomorrow, so next chance I get to ride will be Thursday. I will post results then.
Thanks for all the advice!
2007-08-28
13:21:26 ·
update #1
try it with the petcock in the reserve position. if that doesn't help raise the needles in the carbs, they should have 3 notches for the c clip on the needles, if yours doesn't have more than 1 notch use 1 or 2 aluminum pop rivet washers under the clip. if that helps but doesn't cure it you need to find about 5% bigger main jets or measure them & find or make a drill bit to bore them out. the jets are brass so a D bit made from the right size sewing needle will drill them. but measure what you have first then calculate only 5% more each time then try it out so you dont go too big. usually it only takes 1 or 2 times to get it right, too rich is better than too lean.
make sure your air cleaner is clean before you do anything else, if your running one.
2007-08-28 09:16:22
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answer #1
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answered by Who Dat ? 7
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Now, before starting on the carbs you must make a decision Performance or economy.they Mike's Xs will have recommendations for .each for jetting out the carb.. Next order a kit from Mike's Xs. that have the o-rings for the needle seat and new needle and gaskets The jets are cheap so new ones won't be that much. If it has been lagging perhaps buying two of the needles may help if it has multi slots.
Buy a gallon of Berrymen (walmart) or other Carburetor cleaner. Disassemble the carbs and allow them to soak for a couple of days. . Use the Chem 14 spray cleaner to make sure you have all the Berrymen Carb cleaner off of the carbs parts If it has been lagging perhaps buying two of the needles may help if it has multi slo If you choose not to change any thing make sure you have a brass brush and a gem clip available to port thru the jets
there are a couple of rebuilding primers on. xs650 cental and garage.
oh yeah you are building 2. You will 2 kits 2 jets high and low 2 needles etc
and get you a gas filter about 2-3 bucks to keep any crap in tank out of the carbs after building. Use Iridium plugs will add about 2 hps to bike K&N filters about 80 dollars and the spark may be weak get new coils and wires for it.
2014-04-19 14:57:26
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answer #2
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answered by phil 1
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Fluffing at full throttle implies the main jets on the carbs are too small or the balance of the carbs is slightly out. Probably worth taking them to bits in case one of them has a sticking piston or diaphragm damage.
2007-08-28 12:28:50
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answer #3
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answered by Anonymous
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My guess would be that you need to make some adjustments to the carburetor. Used to have a '74 Yamaha 175 Enduro, and that was constantly giving me carb problems similar to what you described. Unfortunately, I can't prescribe any help, because I never learned how to maintain a carb. Sorry!
Good luck!
2007-08-28 12:28:44
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answer #4
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answered by Jeff L 3
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this is usually associated with a fuel problem. when I had my bike I noticed that at wide open throttle I was actually floating the valves. I would pull the fuel shutoff valve and look at the screen inside of it. then work your way down to the carbs
2007-08-28 12:26:27
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answer #5
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answered by Christian 7
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Dude! she's almost 30 years old. Give her a break, You rebuilt it? Check my 360 site to see my old XS650 special. It cost me major dough to keep that puppy in good condition. You need to get a Buell. XS650 Yammie. Yep, I would kill to be able to ride one again.
2007-08-28 12:49:35
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answer #6
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answered by rifleman01@verizon.net 4
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You need to open and clean the carbs. You have constant velocity types with slides that stick very easily.
2007-08-28 21:35:50
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answer #7
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answered by Nomadd 7
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adjust the valve lash they are floating
could also be choke partially engaged or sticking throttle slider
run high test gas
get rid of the stock air filter and switch to K&N's, air is restricted thru the stock ones
2007-08-28 12:27:32
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answer #8
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answered by Gravy B 5
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the diaphrams might be tired or playing up, air filter has leaves in it or dirt...
Fuel filter is blocked on the tank, petrol cap vent partially blocked... dirty main jets, worn needles..
Invest on electronic ignition.
2007-08-28 19:19:52
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answer #9
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answered by Anonymous
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