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Here is a good video on how to do it. Different bike, different coils but you will get the idea. If your coils are okay then at the very least it is one thing less to replace. Good luck.
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I have 2002 road star midnight. I lost completely spark on all 4 spark plugs. Before bike was running OK but sometimes on low RPM while idling would skip a firing on a at least one cylinder making spufff like sound. I put new spark plugs, and wiggled a little coil wires. Bike with new spurk plugs would not fire up at all. Checked for spark on all 4 spark plugs - no spark., not even an electrical I lost completely spark on all 4 spark plugs. Before bike was running OK but sometimes on low RPM while idling would skip a firing on a at least one cylinder making spufff like sound. I put new spark plugs, and wiggled a little coil wires. Bike with new spark plugs would not fire up at all. Checked for spark on all 4 spark plugs - no spark., not even an electrical charge going to spark plug. Went back to coils. Each coil (there 2 of them) has 2 spark plug wires and 2 ignition timing signal wires connected to them. I realized that these ignition timing wires contacts are corroded to the point they would not conduct a charge from the distributor to coil. CLEAN ALL THE TIMING WIRES Contacts on the coils. I did that and bike fired up right away and started running much better without sputtering or skipping a cylinder firing. SO DISCONNECT ALL THE COIL WIRES AND BRUSH THE CONTACTS WITH A SMALL METAL WIRE BRUSH.
find a running sr 250 and swop his cdi unit with yours if the bike runs, fine. if not put his cdi back in and try again. if the good bike now starts it will indicate that your cdi is faulty. the cdi is located under the tank inside the frame. don't buy a second hand cdi unless you can test it on a working bike. they are very expensive and you don't want to buy a dud
have them test the cdi box. it is your electronic controler for your ingnition timeing. it could be getting hot and shuting down. when it shuts down. the can take a wire from the negative side of the coil and ground it to the frame touching it and letting go of it instintly and if it sparks its not the coils it will be the cdi box or something to do with the electronic pickups in the motor that gives the signal to the cdi. that it is the correct time to trigger firing. hope this helps out.
Did you check the resistors on the spark plug wires? Too much resistance will prevent the plug from firing. Sounds like the CDI box is shorting or the wiring harness has a defect it in somewhere in the routing thats heating up after 30 minutes. Yamaha coils very seldom fail, however the CDI box is a common problem on these bikes. Good luck, hope this helps.
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