NRA4LIFE

After checking your valve clearance (.005-.007 Int, .008-.010 Exh) , if that doesn`t cure it, I would check the fuel pump pressure (48-53 psi)

I reread the thread and didn`t see if you drained the fuel and added fresh. Maybe you did and didn`t mention it? If not, catch some from the float bowl in a clean container and see if is laden with moisture. With gasohol, it can suspend quite a bit of moisture before it separates. In earlier stages it just gets somewhat cloudy.

If you find you have to look at the carb again, get a set of torch tip cleaners to make sure the jets are fully open. The slow jet opening will only be approximately .015"-.020" , so make sure you have tip cleaners that go down that small. The aim here is to get any goo out without making the hole larger.

Check the fuel condition or better yet, just drain the tank and carb and refill with fresh. If it still bogs, pull the carb off and make sure the slow and main jets are fully open. Also, while the carb is off, make sure the slide diaphragm is not ruptured.

13.5 volts is a bit low if your battery is healthy and fully charged. As Mech said, 13.5 can be adequate, but 14.5 volts (give or take) is what it should be putting out ideally. Try this, after the ATV has sat not running for 15 minutes or so, see what your battery voltage shows. A fully charged battery will show about 12.25-12.5 volts. If it does not, then unhook the ground and give the battery a charge. A lower amperage charge for a longer time is best. Then retest. If it does show fully charged then just keep checking it from time to time. If it does fail at some point, given the fact it is a magneto CDI system and has a recoil starter it won`t leave you stranded. As mentioned, the neutral indicator bulb would be a prime suspect. The aren`t exactly a common bulb, so to do a quick check you can often put the reverse indicator bulb in.

Super

Here`s the mag coil specs from the manual. It`s for the fwd model, but it`s the same animal. It clearly shows 460-560 for the pick-up and 270-330 for the source coil. Also, notice the wire colors listed match his machine. Again, the stators that have a low resistance on the charge coil (Yamaha calls it a direction detection coil) are for newer machines. Those are what is called a DC CDI system. Those require a battery to work properly. The 1999 model was an actual magneto CDI system. The magneto CDI systems will NOT have voltage going to the positive side of the ignition coil until you are cranking. The DC CDI machines will have when you key on. I agree that a 500 ohm pick up coil is way above the norm, but that is what they used on that model. The Kawasaki KLF300 and many others used one that high as well. For a second opinion on the 500 ohm pick-up coil theory, call Rick`s Motorsports and they will be able to confirm. https://ricksmotorsportelectrics.com/Trigger-Coil:-500-OHM-21_503 Unfortunately, the PDF manual I have omitted the 1999 wiring diagram. I do have a factory manual at the shop on microfiche (yes, I`m that old 😀) but displaying it here would be difficult. Sorry for all the quote boxes, I accidentally added them and don`t know how to delete them. Also, my replies are slow because I`m a newbie here and my posts must be approved by a moderator. You guys were there once 🙂

Mech, with all due respect those figures are correct for a 1999 model. I took them right out of a factory Yamaha manual using the 1999 supplement. The lower ohm readings like you have observed are for newer machines. Rick`s also has a 500 ohm pick-up coil listed for a 1999 Big Bear 350. https://ricksmotorsportelectrics.com/Trigger-Coil:-500-OHM-21_503

One other thing, when you pull the stator cover, disconnect the battery. This helps insure you finish the job with the same number of fingers that you started it with 🙂

The W/R to W/G should show 460-560 ohms, so that is a problem. Yamaha (and others) call that a pick up coil. As far as Yamaha is concerned it`s all one piece, but if you are good at soldering you can get a quality 500 ohm pick-up coil from Ricks Motorsports (part # 21-503) and install it. I have used Rick`s products for decades and they are very good quality. Don`t waste your time on a Chinese stator or pick up coil, they are usually junk. One nice thing about that engine is, the stator is mounted outboard of the flywheel and not under it. This keeps you from having to pull the flywheel. It can be patched in either inside the engine or by running the wires through the rubber grommet where the wires exit the engine cases. If you go with Rick`s coil, because it can work on other brands, the color of the wires likely won`t match. To get the polarity right, I just set the coils next to one another and note what color wire comes out which corner and match that to the new one. Don`t worry, if you get it wrong just switch the wires at the stator plug. If you decide to run the wires through the grommet, you might want to temporarily twist the wires together and confirm spark before soldering them. As an aside, I think one thing that was causing confusion was the fact it appears Yamaha only used that stator on the Big Bear 350 one year. The way Yamaha does some of their manuals tends to be confusing. They make a manual and they put all the yearly changes they`ve made at the end as supplements. That machine came out in 1987 and it saw a fair amount of ignition system changes, so you would have to jump back and forth to make sure you are using the correct info, especially on your 1999 model.

Hello. I will try to guide you through the steps to diagnose your Yamaha. First off when you check the spark, make sure you are using a new plug or at least one that is working in another machine (sorry, I had to say that). If you still have no spark, then unscrew the plug cap and hold the plug wire a tiny bit from a good ground. Sometimes people are dealing with a spark so weak it won`t jump .025"-.035". If you have confirmed that you have no spark, then In my experience (about 40 years) on these particular Atvs, the mag coils fail more often than anything else. BUT, given the fact it ran when parked in a barn, I would suspect that mice may have damaged the wiring. First off, I would do a continuity test to make sure the mag coils are actually making it to the CDI unit. So do your tests right at the CDI connection. The manual I have for the 1999 shows the source coil (brown to green wires) having 270-330 ohms. The pick up coil (white/green to white/red) should have 460-560 ohms. Let me know what you come up with and I`ll try to respond when I get a minute.