Mech

You said you fitted a new stator.. Trace those wires to the cdi unit and then use a gauge to check they have continuity, and if they do, then check that they both have some power coming out of the stator when the motor is being cranked over.. One pair of wires should have an AC voltage, and the other pair should have a single pulse wave once per rotation of the crank. You might have trouble detecting the pulse with a digital meter, an old fashioned analogue gauge will show it clearly.

"It acts as if it’s bogging down because of too much load. I haven’t personally shifted it through the gears on jackstands but I was able to drive it from the front to the back yard in first gear just fine while walking alongside it. But then when I got on it and tried to drive it, it tries to go but acts forced to shut off". Ok. That's interesting, and telling. Not sure what it's telling us just yet but it's going to be an important clue I think.. I wonder if there's something wrong with a brake cable or suspension part that's causing the brakes to come on and lock on when your weight puts the suspension down. I've seen brake shoes systems jam the brakes on because the backing plate was loose or the wheel could move backwards pulling the brakes on.. Normally if you got the brakes on so hard that it slowed the bike right to a stop the engine would have slowed to it's idle speed and the centrifugal clutch would have started slipping.. perhaps though if the brakes get jammed fully on fast enough the centrifugal clutch doesn't have time to let off.. Couple of things.. Try sitting on it and waddling/getting pushed forwards to see if the brakes jamb on. The plate clutch is connected to the shift lever and it gets disengaged when you push the lever up or down(to help gear changes when the centrifugal is locked up), so you can use the shift lever as a clutch lever if you only press down a little. If it's adjusted right it will slip the clutch before it changes the gear. You could use that feature to experiment a bit and try to see if the lockup is in the engine or in the gearbox.. Hopefully you will have eliminated brakes/suspension as a cause before then.

Oh.. That front brake I mentioned that might make the engine rev limit isn't right.. I meant to say the front brake lever that puts the park brake on, so the left lever.. not the right/front brake lever. The start inhibit can be over ridden by applying a brake light, right lever or foot pedal.

Yup, if they have boots they don't need routine greasing. They'll be greased for life.

And in relation to Gw's suggestion, I don't think the bike coming to a stop should cause the engine to stop abruptly because once the engine revs drop as the bike stops moving the centrifugal clutch should start slipping. So, do you think it's killing the engine because there's a wire somewhere that's seizing out because you are sitting on it, perhaps a wire shorting under the seat say, or because the bike moving causes a wire to short out ? Does it feel like the engine stops then stops the bike moving, or does the bike stop moving and then than engine stops because of that ? You should be able to detect that by the sound of the engine, whether it stops firing in a single firing, or whether the bike stops moving and as it's happening the engine sounds like it's labouring. And, after it's come to a stop, does it restart ? After it's stopped, can you push the bike forwards or backwards (try both directions) ?

And.. this bear tracker.. Is this four wheel drive or only two. If you give us the year, and model designation suffix, I could have a look in a service manual so I know what I'm dealing with.. I'm not familiar with yamaha.

Oh ok. So you need to figure out where in the engine, gears, driveshafts, wheels the problem is.. So.. You are saying it can be operated if it's jacked up ? But locks up when you try to drive it ? Right ? And so can it be operated in all the gears when it's jacked up ? When it locks up, does it grind to a halt over the foot or two, or does it come to an abrupt stop ? It'd be good to decide if it's something grinding to a seize, or a chunk of metal getting stuck in a gear. Does it always move the same distance before stopping, or can you get it to go further by driving with less throttle, or in a different gear ? Have you checked the oil for signs of metal, either steel flakes or dust ? I'm assuming that you have tried turning the driveshaft and rear diff, wheels while/when you were working on the driveshaft..

Better mention.. before you rip it apart.. haha.. The plate clutch can be adjusted. You should check the adjustment if the push test does indicate it's that playing up. There's no adjustment on the centrifugal clutch.

"after a foot or two and dies out and won’t drive. ". The engine isn't dieing is it ? It's just the drive stops happening and the engine revs freely ? Yes ? If it is that, then it will be one of the two clutches it has. They are probably accessible with the engine in place. You can test which one is slipping by putting it in a forwards gear and trying to push the bike forwards. If it's hard to push and tries to turn the engine over then the worn clutch is the centrifugal clutch, but if it pushes easily and doesn't turn the engine over it's the plate clutch that's slipping.

That's true too Gw.. The kill switch could have a partial short/contact caused by corrosion.

But it was the key switch you used.. That's the one that would logically have the problem.. You should/could try bridging the key switch with a small jumper wire.

Key or kill switch has dirty contacts/lost movement ? You would I presume have used one of the switches to turn it off between your ride, and the buddy arriving.

Yeah... So get posting.. You should be able to trace and check the continuity of the wires from the stator to the cdi by their colours, and confirming it's a good wire with a multimeter.. You could try a new spark-plug, and/or try removing the cap of it's lead and checking for spark. You could disconnect the kill switch, either at the switch or at the cdi(which would be better). These are all things the book is going to say to try.

7.31AM on the second day of 2025 here already.. World leaders we are.. Haha. Hope you all have a good year..

I must be looking at the wrong wiring diagram. If you can't find the PCM on that bike, it might not have one.. Maybe... If that is the case, check for 12v on a red wire on the back of the ignition switch..

Ok well you really need to get the service manual for it, and then check that the power from the two windings that run the cdi are getting from the stator connections to the cdi unit. I think your "ECU" is going to be the cdi. It will have an orange wire going to the ignition coil if I'm right. You could disconnect the kill switch wire from the cdi, at the cdi. Get the manual though.. It talks you right through the diagnostic process for no spark.

No I don't. They won't be hidden though. They will be easily accessible.

You should check the fuses..

The timing can't have been 180 degrees out.

A colder plug will oil up easier..

A spark plug missing only under low load is a new one to me.. for a carb engine anyway. EFI does that, but never found that with a carb engine. You should do the valve seals when doing the work. If they have sat for a few days and evaporated the fuel out of the carb, then the fuel pump sometimes takes a while to pump fuel through, especially if the engine has low vacuum.

Well you've come to the right place. Welcome along. You need to make ten posts to qualify to download a service manual, (which is what you need), so tell us about the bike's history as far as you know it, and perhaps a bit about you and your son's experience riding and/or repairing bikes. It'll help us a lot when we are giving advice if we know you or the son are familiar with bikes and engines etc.. or not.

Depends where the "pop' is coming from. If it's under load and out the exhaust it may may an electrical misfire. If it's out the carb then it's probably a lean mixture. But... the no idle and popping could be caused by valve clearance or valve timing. You really have to know one part of the system is absolutely right before you start looking at the next possibility. Valve clearance and timing is simple and doesn't take any discrimination or experience to judge. A new spark plug is simple and cheap to replace. The carb, which is from the sound of the description (symptoms and circumstances), the most likely, needs to be right for that bike. If the carb's been set up to be mounted flat it may not run well on a bike where it's mounted at an angle. You need to use some discretion when checking the jets and settings. If the float level's set different by the manufacturers because it's for another model bike, then the jets may all be suited to that float level. I always check the float level seems right for the way it's being mounted, then ride it taking careful note of all the symptoms and the circumstances they occur under trying to figure what part needs adjusting or changing. I only ever change one thing then go for another ride taking careful note of what effect that had to the fault, and whether it's made other ranges of throttle better or worse. The three jet systems in the carb, idle, mid-range and full throttle, all overlap, and there are special features that help with the transition from one system to the next. The usual way to set a carb up is, get it idling and running, test ride and set the main jet system, then recheck the idling system, then set the mid-range system. Sometimes we have to go around the cycle doing all three again if it was a really badly chosen or set up carb. It takes time, a lot of careful test riding, and a good understanding of what's going on.. That's why it's always best to stick with the original carb.

"when engaging throttle it runs smoother, but when disengaging or hovering throttle at a constant rpm, it bucks, no matter what gear its in.". Ok. Good observation. Sounds like a carb problem (or problems). The no idle after a run is probably going to be something that an adjustment of the idle will cure, and it may even help with the stuttering.. Another simple thing to try now would be to change the slide needle position in it's clip and flex and inspect the rubber diaphgram. That can be done in place. Then if that doesn't fix it I think I'd pull the carb off, clean it and check all the jets are clean and what size they are etc, set the float height carefully to a height appropriate for that bike. Carbs for some bikes sit at an angle and others sit flat, and the same carb can be used for both situations, but they have their float heights set different to suit the angle.

I'd imagine it can be done with the engine in place ? Most can. The service manual says what can be done with the engine in place.