Hi, Lorant and the usual suspects are:
1. Fouled spark plugs.
2. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
3. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
4. Loose connection at ignition coil or plug between ignition sensor and module.
5. Spark plug cables in bad condition, shorting, leaking, spark plug cable connections loose check for spark leakage in the dark.
6. Faulty ignition coil or electronic control module.
7. Faulty CKP, CMP, or BAS sensor.
8. Faulty ignition switch.
9. Tilt sensor needs a reset.
10. Security alarm failing to disarm needs reset
For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day. 49cc 2 stroke engine scooter has no spark Help GY6 Electrical Troubleshooting Tutorial No Spark Eliminator Yamaha XC125 Service Manual OEM parts for Yamaha YAMAHA CYGNUS XC125 Owner Manual
Did you check/clean your air filter? I had a no start issue with my Yamaha RD350 where the filter box was tight up against the seat and no air was getting into the carb. Do you have compression? Is the cylinder still attached by the connecting rod? Have you recently made any changes (like new jets) or repairs to cylinder or rings?
usually it comes down to an air intake issue if you have a working cylinder in a motor with gas and spark unless your timing is so far off that it isn't firing during the compression. But it might still backfire if it's off?
I always add about 10% oil to my small engines to help protect them from friction. If it starts ok with that much oil, it might smoke a bit and cause a little carbon build up on the plugs or valves, but most engines after 1980 are high enough heat and compression ratio to clean themselves up.
Sometimes the oil doesn't blend in all the way without some sloshing around.
Hi, Allen if your bike has been sitting idle for months or years and you did not do any pre-storage maintenance I feel your pain it will probably have a dead battery and not want to start or if it starts it will not idle unless the choke is full on and run poorly then stall, here are the following steps necessary to complete in order to get your bike back to an acceptable running condition and in the future pour in a bottle of fuel stabilizer and injector cleaner for you FI folks at least 2 times a year and before storage.
1. If your battery was 2-3 years old when you last had the bike running you should replace it.
2. If you believe your battery might still be serviceable remove it from the bike and put it on a 1 or 2 amp trickle charger for 24 hours. If it is the old lead acid type with visible cells and acid levels fill each cell to the top line with distilled water and replace the caps, run the vent tube into a plastic or styrofoam cup, any cells that are cloudy/milky replace the battery.
3. After charging the battery remove the leads and let it sit for a couple of hours then check the battery voltage with a voltmeter, you should have 12.5 volts or more, any readings in the 11 volt range you need to do a proper "LOAD" test on the battery and replace as necessary, you may have 12.5 volts or better but little or zero amps, any readings in the 10 volt range you have a dead cell and the battery needs to be replaced.
4. Drain and flush fuel tank if it rusty there is a cheap and easy fix. https://www.youtube.com/watch?v=fUYr_7SwGms
5. Remove and inspect your air cleaner paper elements that are not oil soaked can be cleaned with a soft brush and low pressure compressed air, oil-soaked elements must be replaced. Gause mesh and foam elements can be cleaned by soaking them in a container big enough to completely cover them with a solution of 1 gallon of water and 1 oz. of Dawn dishwashing liquid for small and medium size elements, for monster size double the formula and let soak for at least one hour then rinse with warm water shake off excess and let air dry, "WARNING" do not use compressed air as this will embed micro-sized dirt and road grime and destroy the mesh pattern and stretch foam elements out of shape just squeeze it like a sponge and let air dry, use a fan if you're in a hurry. When completely dry spray a very fine mist of air filter oil evenly around the whole element.
6. Remove the carburetors, disassemble and decontaminate with a "CARB DIP" or if you have EFI remove injectors and clean with carb spray and compressed air
7. Check intake manifold and seals for leaks and craks.
8. Remove fuel valve and filter disassemble and clean as necessary, remove, clean, and inspect fuel and vacuum lines and replace as necessary.
9. Replace spark plugs with new ones and check for spark.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day. https://www.motorcycleforums.net/threads/v-star-650-idle-issues.48035/ https://www.youtube.com/watch?v=8QtmvhOLSLA https://www.manualslib.com/manual/833178/Yamaha-Xvs650.html https://www.partsfish.com/page/oem-parts-for-yamaha https://www.manualslib.com/manual/659403/Yamaha-V-Star-Xvs650p.html