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Jeff Policky
Jeff Policky, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 2425
Experience:  Yamaha Gold, Suzuki Gold, Honda Bronze, Polaris Bronze, BRP
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I have an 87 yfm 80 yamaha i only owned it a week before

Customer Question

Hello i have an 87 yfm 80 yamaha i only owned it a week before it developed a spark problem. First I could charge the battery on the machine and it would run for 10 or 15 minutes with a good spark eventually I will lose this all together. I bought a new battery replaced old one. The problem was fixed I thought it ran good for 2 months then over the winter its at and must all that spark completely so this spring being that I'm not that mechanically inclined I decided to start swapping out parts on it after doing research online I started with changing out the stator which came with both coils attached I bought this brand new but it did not help so I thought I may have had a bad ground and I bought a new wire harness and checked all the grounds and still a very weak were no spark either way very intermittent and weak so then I bought a new ignition coil and still same problem so my question to you is now that I have replaced the stater including both are charging coil and pickup coil changed the wire harness and put a brand new ignition coil on it including new plug and still have a very weak or intermittent spark so weak the machine wont fire if I buy a new CD i is that guaranteed to fix the machine and give me a spark
Submitted: 2 years ago.
Category: Motorcycle
Expert:  RSRBOB replied 2 years ago.
Hi and thank you for your problem.Although it may not have been a complete mis-step to replace all the components you did, it sounds like you have a charging system problem more than an ignition system problem. For the ignition system to function properly, it must have battery voltage going to it, so about 12v. If the electrical system is not recharging the battery, it would give the symptoms you described. It runs good right after charging the battery but starts running worse and worse as the battery dies. In addition to the wiring harness and stator, you also have a rectifier in the charging system. The rectifier changes the AC voltage produced by the stator into DC voltage so the battery can store that electricity. If you have the ability to test the rectifier, we can do that. If you are not familiar with a multi meter, I suggest removing the rectifier and taking it to a motorcycle shop and having them check it for you. Suggested retail on the rectifier is about $90. It is a half wave rectifier so it shouldn't take a dealer more than a few minutes to check it. A rectifier is a series of diodes, which are essentially one way valves for electricity. That means when they are functioning properly, they should flow electricity in one direction (polarity) and NOT flow electricity when the polarity is reversed. However, Yamaha states in their service manual that you check all connections first, then continuity through the charge coil, then amp output at 3,000 RPM (0.7 amps or more) and at 8,000 RPM (3.0 amps or more). Sadly they do not provide ACV tests for the stator or resistance/flow direction for the rectifier. Their directions tell you to check the stator, wiring, battery, fuse and Amp out put and if all that is fine, replace the rectifier. Still, a shop should know what they are looking for and be able to advise you as to whether the rectifier has failed. Considering you have replaced the stator, the only two options are really the connections and rectifier.If you have any more questions, feel free to ask.ThanksRSRBOB
Customer: replied 2 years ago.

Ok weak spark when first turning over still not strong enough to fire. After a 30 sec of turning over almost no spark. This is after a replacement used cdi brand new stader brand new ignition coil replacement wire harness still weak intermittent spark

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