Mech

If you look in the workshop manual it says to use regular old petroleum oil. A lot of the more modern oils, whether synthetic or petroleum, have additives in them that aren't really doing anything useful in a motorbike engine, and which could even be doing harm. I stick with petroleum oil in my bikes, and of the spec they stipulate.

Never heard of such a thing. How many wires on the vehicles kill switch ?

The suzukis hold a lot of oil up in the valve case. It could leak a lot of oil down the guides. Given the circumstances you describe, I doubt it's the rings. Oil's cheap..ish.. cheaper than getting your motor worked on by a shop. And no I don't think a smoking suzuki is a common thing.. I've had lots through my workshop and started them cold and I don't remember ever seeing one smoke bad at cold start.

You need to tell us what vehicle the kill switch is off, and what it's going on.

If the 10 grade oil you are thinking of using isn't synthetic, then you shouldn't mix it with the synthetic oil that's in your motor. Perhaps it would be easier, and give peace of mind, to do an oil and filter change right now. Then you can put regular petroleum 10w30 in it and have some to top up in future. Petroleum oil's about half the price of synthetic. If you have to buy much synthetic(due to packaging practices) to do the top up, it won't cost much more to buy a pack of petroleum and do a change.

Do those things have two throttle cables going into the carb ? Perhaps one bike has a different/faulty cable splitter box. Perhaps the cables need readjusting for the different carbies. Did you try the other bike, with the other carby ? How did it go?

Since it's got synthetic oil in it now, you need to top up with synthetic oil. It doesn't have to be the same brand, but you should try to get an oil with the same rating... Probably SF or SG. If you want to change to a straight petroleum oil(non-synthetic) you can at the next oil and filter change.

First thing is probably to undo the bleed nipple on the left front wheel. If fluid comes out and then the wheel turn, you have a problem in the brakes hydraulic system. If releasing the hydraulic pressure makes no difference then it will probably be a wheel bearing, or one brake shoe has jammed itself on. The lining can come off the brake shoes and jamb up in there. You could try undoing the wheelnuts and taking the wheel off, and then try to get the brake drum off. If it's a bearing that's the problem, then the brake drum should wriggle around and come off fairly easily. Brake drums get a bit of wear where the shoes run on them, and it's sometimes necessary to manually release the self adjusting brakes to pull the drum off, but if taking the wheel off allows the drum to move in and out a little, and wobble around when you grip it top and bottom or front and rear, then it probably won't be the brakes causing the problem. If the brake drum seems locked solid with the wheel off, and can't be moved in any direction then it's probably a brake shoe jammed in there. To fix that you manually release the self adjusters on the brakes and pull the drum off. If the drum moves with the wheel off, I'd be suspecting a wheel bearing. If possible rotate and pull the brake drum and it should come off. If it comes out a little but then jams and won't turn, you need to use a small screwdriver to hold the brake adjuster's ratchet off while you back off the brake adjustment. Then pull and rotate the drum and it will come off. After that you take the nut off the center of the wheel's hub and that hub should pull off the axle/drive shaft. Undo the brake hose, top and bottom suspension ball joints and the steering ball joint, and then the bearing housing will come away from the bike. Then check the axle turns in the front diff, and check the wheel bearings rotate or not in the housing you pulled off the bike. The wheel bearings are held in by big circlips behind seals. Lever the seals out, use long nosed pliers or proper circlip pliers to remove the circlips, then use a hammer and punch through the centre of one bearing, to knock the opposite bearings out, being careful to move the bearings a little at a time on opposite sides so as to not harm the housing.

https://www.quadcrazy.com/files/category/3-yamaha-atv/ Probably a manual there somewhere.

When the motor's running, the vacuum is in pulses but not as deeper vacuum as what you can suck, so in operation the fuel flow is more of a trickle...If you put the vacuum hose back on, and hold the fuel hose horizontally in a bottle with the motor idling, there should be a steady approximately half flow of fuel. By that I mean it will be sort of half the hoses diameter, but trickling out steadily..

Turn the fuel tap to prime if it's a vacuum operated tap, pull the fuel pump's vacuum hose off the carby and suck hard on it, and when you let the vacuum off the fuel should come out of the fuel hose as a full diameter slug of petrol. Be cautious when you suck the hose because one possible problem is that the fuel pump's diaphragm might have a hole in it and you might get a mouthful of petrol. If the fuel delivery is a full hose diameter pump of fuel, then the pump works. You need to have the hose laying horizontally into a bottle to get a good idea if it's a full flow. If that works then you need to check there is plenty of vacuum at the carby and that it's getting to the pump. There might be a hole in the vacuum hose.

The dropping off of pressure at the same time it's missing , might be a dirty filter.. fuel filter. Even though the pressure's good at idle, it might not have a good flow. It always pays to check flow and pressure, because you can have one without the other.

Ha. good for you man. Perseverance always wins. Giving up never does. Those choke plungers don't get used often and do tend to seize up. I've freed a few up by using a 6mm flat ended engineers punch, and a light hammer(about the weight of an eight inch cresent), and tapping along the bit of the choke housing that's formed as a tube. Most of the plunger's cylinder is formed in solid casting, but on one side the cylinder wall's thin. You tap back and forwards along the length of that thin part and it expands the cylinder wall, making the cylinder slightly larger, and letting crc soak in. Then use a small screwdriver to carefully rotate the plunger. You have to be careful in rotating it because the plunger, which is slotted across, can spay apart and jam tighter into the cylinder. If it does do that though you can use long nosed pliers to squeeze it together again. They are really soft steel. I can generally get the plungers out and freed up and good to go again with that process..

Yeah ok I googled.. Yeah that looks like lots of fun. For open terrain that would be great. You can also get real tractor model suzuki quads. They are good for places/terrain that need a bit of careful negotiating..

I don't know a Z model. Sounds sporty..haha. I reckon Honda and Suzuki make the best dirt bikes and quads.. Both really reliable and nice to ride, good controls. Dependable, and the farm model Suzuki seem to last forever. Quads with those round tyres are just the best thing/fun for sand dunes.. Hope you enjoy your ride whatever it is.. Unless... are you meaning a DR400Z.. ? I know those.. All the smaller DR models were legendary for the miles they did. My son's got one of those dr400z, had it for about five or more years now and it's been absolutely reliable.

The plastic part of the plug can probably be used again, but if they are damaged you can buy them with a bit of hunting around. And the terminals that go on the wires and into those plugs are real common and any decent auto electrical shop should be able to sell you those. The terminals have some sort of tag, either metal on the terminal, or plastic on the plug, that hold them in. If you look in the front and back of the plug you will see which sort. Use a tiny blade like a screwdriver to flatten/push aside the tag and pull the terminals out towards the wire. https://nz.rs-online.com/web/ Theses guys are in aussie, they have everything.. But there will be someone like it in US..

Yeah they're all fun !! The later models with the crank running forward and aft, as opposed to the early ones which had the crank across the bike, are much easier to do work on.

The smoke at startup will probably be the valve guides leaking oil. It runs down the valve stem. The valve keepers/spring retainer plates aren't meant to, but they act like funnels to drain oil down the valve stem while it's sitting over night. There are seals on the valve stem to stop that, which are probably worn, and it might also have too much play between the valve stem and the valve guide, but, if it runs without smoke once it's warm, (and you really want to look for smoke as you put the throttle on at the bottom of a hill to check there is no smoke then), then it will probably come right with just new seals. I think they might also have an O ring under/on the valve guide where it fit's into the head, but they seldom play up. The top ends of those things have a pile of oil up there when you take the valve adjuster caps off, especially the exhaust one, but that is normal and doesn't normally matter as long as the seals are ok.

https://www.manualslib.com/manual/74835/Husqvarna-Huv-4214.html

Look in behind the front wheel and if it's got axles/driveshafts running out to the wheel.. it will be a 4X4.

Yeah if you wired up the ignition unit and the triggering coil in the stator and the ignition coil it would go with a kick or a jump onto the starter, but it's quite a few wires and probably best to just repair or replace the wiring. Are the wires actually chewed, like a rat maybe ? If not I'd probably just check the wiring and repair the wires that are actually broken or shorted, soldering new lengths of wire in if needed. If it is rats, well they can actually eat the copper.. haha. And.. they have a nibble here and a nibble there and you end up repairing it all over, then it's best to strip the loom and run new wires. Get a manual(I've attached one), then use a multimeter with a buzzer and following the diagram check each wire from one end to the other for continuity. Check the loom for wear on the insulation and tape up any potential shorts. If there are breaks in the wires it will probably be at their ends, where they go into the plugs or terminals. You can get new terminals if you shop around, an auto electrician or electronics shop or.. R.S. Online.. R.S. Online has just about every type of terminal, and plug. You can sometimes pinpoint the break by gently wriggling/bending the wire, mainly at their ends where they are out of the loom, and if the wire's broken inside the insulation it will be extra flexible where the break is. Wires hardly ever break inside the loom, except very occasionally at places where they bend, such as where they go to the handlebars, or go into the stator. Get a roll of electrical tape and someone to give you a hand, and have the friend hold one end of the loom while you strech it out and rewrap the tape, keep the tape tight and stretch it on and it will come out like new.

The wide flat treads, which I think is what you are calling square, they wear badly, make the steering different, put extra load on your wheel bearings and steering, and if they have tractor type treads, drum at speed. I'd stick with the round knobbed profiles they come with. The square tractor type treads are just very marginally better in deep mud.

On sand a two wheel drive honda would be my pick. They have a crawler gear, below the normal first. They are low maintenance and relatively light and nimble.

That bead buster looks like the thing.. ATV tyres are bad news.. And I've done tractor tyres by hand in the field with levers.. but ATV;s are worse.

Looks like half the bodywork, the tank and the racks.. and the tyre looks bad too.. Good that the bolts come loose at least.