ATV Help & Brand Specific Topics

Sorry i attached the wrong manual

So I have an 89 Yamaha moto 4 250cc and when I ride it, itll get hot after like 10-15 mins and then will just die and turn off. It's has new carb rebuild, new air filter, new battery, new spark plug so I don't think it's a crack in the spark plug Can anyone help me?

Good you got it going. Did you have to replace the pump.

I did find this manual not sure if its your year but might help bruin_350.pdf Never throw the OEM carb away, fix it and keep it for a spare if possible.

It's right dickered. Yeah like I've been saying it's MIKUNI so it's clearly OEM. Ordered a new one (aftermarket). Can't get that jet out. It will rotate but not come out. 100% it was originally cause by that corn gas garbage produced by the midwest/western corporate farms. That land needs to make food, instead of pandering to artificial subsidies and contributing to fuel contamination. It's destroying health (corn oil) and destroying our carbs.

From what you describe it sounds like someone screwed in in too tight and stripped the last thread and if you pull up on it while turning it will grab the lower threads and screw out, just a thought, it could be that the threads have disintegrated from sitting in the weather for many years and may just pull out if thats the case you can repair the carb with a heliocoil or better option get another one, is this an OEM carb or aftermarket any markings on it.

So you think it's unscrewed all the way (that's how i found it) but just needs a yank?

Looks pretty bad, but the float chamber looks OK, on the mainjet grabit with some vice grips and pull up at the same time you are turning it might grab the threads .

That looks like the main jet, and it just rotates. Took the side off (the MIKUNI black plastic) rust. Took the bowl off. Carefully punched out the float needle valve pin. Removed. Tried unscrewing what looked like the main jet. No luck. Just turns. Never seen that before on a carb. Special 'Yamaha ATV' feature? Or time for a new carb?

There's no '14 and 17' on mine. Can you just tell me which relays you mean? Pulled the MIKUNI plastic cover off the carb, during removal to detach one of the two throttle cables, and it's gross in there. Will clean and get back to everyone.

Back in business. Runs great again. Thanks for everyone's comments!

Relays 14 and 17 are shown as normally closed. And it's really the cdi unit that's acting like a relay to operate the start solenoid. If either the brake light or the start relay contacts are closed when you push the start button, the cdi provides an earth for the start solenoid. If neither the start relay contacts nor the brake light switch contacts are closed, then the starter solenoid doesn't get it's pull in coil earthed through the cdi unit.

That will work power wise ,check the size requirements needed for the battery tray.

Do you guys know if these types of batteries are all basically the same for the YFM350 models? https://www.amazon.com/CALTRIC-BATTERY-YAMAHA-YFM-350-1996-1999/dp/B01DGLS20Y Like would that work on this one? HxWxD. I assume they do, and amazon simply doesn't have a fitment guide because this model is so old. "THIS WILL NOT WORK ON YOUR 1990!"

This exactly matches what I am seeing. For the two on the left, they are SPST, or simple relays that are normally-open, and only close when power is applied to the coil. Those I removed and individually-tested. I haven't taken the REVERSE relay off to test it. I assume it's the same. Is that what you are referring to when you say normally-closed?

Dash lights are all tested and work. To test, remove the brown and other 3 wires, carefully, as they are 'glued' together from being connected for so many years. Every socket was pulled out and greased with silicone. Each barrel received a small amount of copper paste. All three dash lights work, NEUTRAL too. On the backside, above the brake light, take the first relay off the back. Tested, it works. From the wiring colors, it's the engine stop relay, referred to as the 'Starting circuit cut-off relay'. That was fine, but the contacts somewhat crusty, and the way it was bonded with the plastic indicated it had never been removed, was original. It got the same copper paste and silicone paste treatment. The next was the Neutral relay. That had the same never-been-changed-or-removed characteristics, but the metal contacts were crustier. I didn't bother with the reverse relay for now, since that light is working fine. These are all interchangeable, simple SPST relays. If you have the relay in your hand, and you are looking at the 4 contacts, the locking mechanism facing away from you, then the 2 right-hand contacts are the coil connections. The left-hand 2 are the switch contacts. If you apply 12v to the coil, you should audibly hear and feel the relay energize, click. The cut-off relay sounded good, and everytime I energized it, i got continuity across the left-hand terminals. The Neutral switch relay, didn't make a noise. I tapped it briskly, and then it did. The fix is to tear the top off, where that seam is, and spray some CRC cleaner. Then take a small pick and make sure the contacts are hitting each other. I added a tiny amount of copper paste, too. Once I could energize the relay coil and get a consistent continuity, it was reinstalled and the NEUTRAL light on the dash worked. Also, when in neutral, pressing the START button, correctly actuated the starter solenoid. It's ready for an oil/filter change and a test start.

Ah no I figured out the switches, but note the two relays are different.

#48 The few manuals I've bought offline as pdf files have all been as described and good value. I don't have any particular pay site, I just browse their site checking that they don't just advertise the same manual for all models or anything like that, check the details shown in the manual looks right, then trust Visa to have checked the company is reliable. Mostly though I manage to find free manuals.. Not for that bike though. The electrical system is likely similar to several other models, but, because partzilla say the wiring loom only fits your year and model, it must have some odd combination of switches, relays, stator, cdi, regulator. You could mix and match manuals of different models to get the right stator specs and cdi wiring etc, but it would be quicker and safer to get the correct manual. Show us the site where you saw the manual for download and I'll check it out. Also, in one of those earlier simple diagrams it shows two different types of relays. One relay is a normal open type, and the other relay is shown as normal closed type. It may be that the two sets of contacts are in one unit, the manual will have more details. The neutral and forward/reverse switches operation is not logical as shown. I suspect they must have connected poles if they are all in one unit. The manual will explain. If you don't get the right manual, to narrow down which other yamaha models might have similar wiring, you can use partzilla, or check what the cdi has going into and out of it. It's a good idea to start by counting the number of wires and plug shape of the cdi, then looking through several manuals gathering those diagrams up to be cross checked against the start button wiring.. Once you have a few likely looking possible wiring arrangements as diagrams, then it's a good idea to check resistance readings of the stator and pickup coil and look through the manuals seeing what models had those specs.

If the lawnmower soloenoid is a 3 post when its mounted it grounds, if its a 4 post it needs a ground from one of the post to operarte correctly. Did you tough the 2 big posts together to see if the starter would rotate. You might check your wiring between the neutral switch and light to make sure its good. If still nothing you might take the neutral switch out and clean it and make sure its working properly. Good work! You have been busy, good your oil pressure and reverse lights work. Its coming together a piece at a time. I would also sqirt some oil in the spark plug hole just to lubricate rings before you turn it over and i always use a 2 stroke oil mix for first crank, just a little oil in the gas to help with lubrication.

While I'm coping with looking for any potentially blown fuses or additional relays (besides the main starter relay), by using the "1987-1997-yamaha-big-bear-350-service-manual", what's the best site you recommend to get the specific YFM350ER service manual for 89-90? It looks like it should cost around $10-15 for the electronic version. 1987-1997-yamaha-big-bear-350-service-manual.pdf

If that wiring diagram you posted is correct then the cdi is a part of the start circuit..

@Gwbarm The neutral switch is OK. Tested between the nipple and ground, and got a definitive continuity when in NEUTRAL vs in gear. Can confirm the lamp should be OK, get 6.8 ohms across it. Will test it a little further, using a battery to getting it to light up. The barrel connector that goes over the neutral switch male connector, was kind of corroded. It took a little bit to get a pair of alligator test jumpers to connect it properly to the meter to test continuity. Started to rain so I packed-up, I have to do this outdoors. Will go back at it and see if I can get confirmation of the lamp lighting up and the neutral circuit working. Have you ever heard of the neutral switch and lamp being OK but the light still not coming on? I'll have to look over the schematic.

@Gwbarm Before I spend any more money on this, I should be able to hook up a battery and get the starter relay to click. I bought a sort of standard lawnmower relay-solenoid from the local Husqvarna dealer (for the same price as the amazon yamaha copy $10 one), same terminals etc, although it has standard 1/4" spade terminals that I was able to wire the left-overs from the previous OEM solenoid harness to. And it has a nice mounting point hole/bracket, so all I have to do is remove the screw that holds the CDI on (this is mounted in front of the battery cage, just over where the original relay went), and mount it there. No fumbly straps or whatever yamaha engineers envisioned for this model. I wired in a good battery to the ground strap on the back, with the ground strap to the transmission/motor, and that red with white strip on the harness. Turning on the key switch, I got the OIL PRESSURE light for a few seconds, then it went off. I was able to use the side-bar HLR to change it into REVERSE, and the REVERSE light lit up in red on the dash, and switch it back out of reverse and the light went off. So both of those lights are working and the ATV is getting power. Could not get the NEUTRAL light to come on or the relay to click, and my guess is that circuit is hooked to a start inhibitor, so unless the harness and sensors think the unit is in neutral, the start button won't do anything - will not fire the relay. A new sensor is something like this?: https://www.amazon.com/dp/B01MQE3DYF I'm going to look through the service manual I have that is close, and see if I can find a part number and also the partzilla catalog. My guess is the neutral switch went bad at some point, which further would make the PO decide to completely bypass the switch, the relay, and the inhibitor - essentially the entire wiring harness. I'm kind of glad he did, instead of butchering the original harness. I have the SUPERTECH 4-STROKE ATV/UTV oil (3 qts) and 1 qt of the SUPERTECH full synthetic 75-90w, and will do an oil change before actually turning it over. Besides that I have to inspect the carb. It's just loose like someone tried to do a cleaning and never fully remounted it.

That's correct. I went on partzilla and they share the same part number for the plastics between the bruin and big bear 250cc ONLY.

Good, thats definately the best option, but i may be wrong about the fitment according to the Ebay ad it says it fits the Big Bear and the Bruin.