Mech

I think the regulators fail for a reason Randy.. not because they are inherently faulty.

I don't think the regulators are as bad as Randy seems to think. I'd check the regulator, when you fit it, has a good earth, and that there are no bad connections between the regulator and the battery.

But you didn't adjust the valves ? And it hasn't gone since ? Test the oil as I say.. see if it's water soluble..

Good one !

There's an owners manual too. At the top of this page, "more", then "owners manuals", which takes you to a new page, then on the right choose the make. You need to make ten posts before you can download..

I presume it was running fine before this work ? So you'd changed the plug and oil both together and at the same time ? And you tried starting it and it wouldn't start at all, didn't fire even ? So did you check the sparkplug, which would of course be the obvious problem ? And if it did never start after the service, how long did you crank it before testing the compression ? If the oil was bad it wouldn't cause enough wear, that fast, to lower the compression. I'd suggest the rings are stuck in their grooves. I'd also suggest you use a screwdriver or something and dip a bit of the oil out of there and see if it will wash off/dissolve in water.

Yeah the cables are real tough, there's no way you could snap one.. it must have been a crook cable, with broken strands snagging, till you broke the last few,

Older model but it may be the same.. https://www.manualslib.com/manual/998189/Yamaha-Yfm400fw.html?page=2#manual

This looks air cooled... https://www.manualslib.com/manual/659758/Yamaha-Big-Bear-4x4.html?page=10#manual The pages load quickly if you want to preview it before downloading..

I generally look up a parts place online and start comparing parts. Some parts places when you look up a part, will tell you what else that part fits. So.. if you look up your brakes, and fuel system, and transmission, and then check what other models have those same combination of features, that narrows it down often, then you could look up seats and bodywork, speedo, lights.. racks, electrical parts, carbies are a good one to check, they vary a lot with markets and years..

Thanks.

I was trying to imagine last night what could cause it to get two gears at once, because they have interlocks to prevent that, and the only thing I could think of was that perhaps the shaft can get end float causing it. It might pay to check the shafts can't move end-wards if one of the nuts holding the clutch on, comes loose.. or the selector barrel looks like it's located in a bearing that prevents end float, by the detent plate and a small bolt.. If the denent plate was loose, the changes wouldn't work right, and the shifter forks could move the gears along and possibly engage two gears at once. The detent is in the outer case.

Those things don't have a vacuum operated tap do they, or a vacuum operated fuel pump ? If it doesn't have either of those, then I'd ignore it for the time being. If it has either of those, check the vacuum hoses for fuel in them. I'd ignore it and see if it plays up again. If you've checked the tap, and it is closing off correctly, then I'd guess you might have turned the tap on intending to start it up and move it, then pushed it out instead, and forgotten to turn the tap off ? The float needle that sets the fuel level can leak if the tap's left on, and cause a carby overflow, but still operate fine in use without any problems..

I was just thinking it might have be easier to pull the sensor wire off and out to where you can get at it, then back probe it and refit it up in the confined place, but if not then not. Keep riding and see if it doesn't just come right. The suzukis over here seem to be fitted with an after market handlebar push-button switch to turn the fan on. They originally came out with only the oil temp switch for the fan, but within about two years started appearing, from new, with a handlebar switch as well. I'm in a forest here and on steep land, and it's often sweltering and no wind, so I use my manual switch quite a lot on summer. Easy to rig up.

Good stuff. For what it's worth, I'd recommend NGK spark plugs.. I don't know why but as long as I've been riding jap bikes(fifty plus years), nothing seems to last as long or be as reliable as NGK..

It does sound like inside the main cases but it's a good idea to take the control cables off first and check if it can be changed and put out of lock up somehow. They have to come off to get the motor out anyway. Then if you end up taking the engine out it would be an idea to take the side cases off and inspect the gear change mechanisms for some simplish problem, before taking the head and barrel off. I'll have a look at a manual...

Yup, if the output shaft is locked solid it's either something seized, such as a bearing, in which case you'd probably be able to get a bit of movement out of it by forcing/rotating the output shaft back and forwards, or as Dave says, the gears are stuck in two gears. The later sounds more likely since the shift doesn't seem right. If it's a four wheel drive.. perhaps the front diff is playing up.. It's a solid drive between the front and rear drives, and four wheel gets engaged in the front diff.. Well that's what our local models are like, but we don't get eigers. If you can't suss it let us know, and what you have found, and I'll download a manual and have a read..

Ecu coolant temp sensor... https://www.mickhone.com.au/partFinder/fiche/suzuki/2011/lt-a500xp/cylinder-head#next Part 31. The air temp sensor would have to be a mile out to cause your problem probably.. Ignore that one. The ecu water sensor, I haven't had a read up but it's possible you may be able to test it roughly with it in place. You could pull the plug off and try a resistance test on the sensors terminals, estimating what the water temp is by either having a temp probe in the top of the radiator, or using a temp reading gun thingy, or, you could test it by carefully getting the water-proofing plugs out of the back of the plug where the wires go in, and poke pins in there carefully and test it running with the ohm or volt gauge.. Don't damage the water proofing. they are sensitive and getting water in the plug could cause problems. The radiator fan sensor/switch is on the top of the radiator, and that's the one that is probably causing the red light. If it seems nearly right now, it may come better with continued use..

Once you have the manual, you could trace every wire using an ohm gauge to check for continuity from one end of each wire to the other end.

Inspect the loom for any signs of chafing, then check at the ends of the wires where they go into plugs looking for dirty/corroded connections, and wriggle the wires just there looking for any that flex too easily, indicating the wire's broken inside it's insulation. All of the electrical component tests are spelled out in the manual.. Most of the testing you can do without the bike running, using an ohm gauge. After you've made ten posts you can download a manual from this site, up the top, in "More", then "atv service manuals", which takes you to a new page, in the new page on the right and down a bit you choose your make.

Sudden loss of power, yes check the spark. If it slowed and faltered first.. check there's petrol getting though..

Reverse the wires.. See my post above. It's too complicated to explain all the possible variations but it's very likely that turning the key off allows the cdi to drain of power, which then means the first negative pulse of the trigger fires the cdi, after that, the cdi's charged(incorrectly) to a positive charge which won't allow the negative pulse to take the trigger voltage low enough to trigger the cdi.. Cdi can need a positive or a negative pulse to trigger them, and they can trigger on a rising or a dropping point in the ac wave. Swap the wires, one pair at a time. First reverse the cdi charge wires and try, then try reversing the trigger wires and try. Then, leave the trigger wires reversed and swap the charge wires back to how they were originally. You need to try every combination..

You mean the cam timing ? If it always seem to be a half tooth out, you need to move the crank one tooth which equals a half tooth of cam movement. Put the crank on it's mark, and take hold of the timing chain at the top next to the cam sprockets mark. If it doesn't have a mark at the top, use a marker and put one there. Holding the chain by one link, by themark, slip the sprocket down and out of he chain, then holding the chain up tight, rotate the crank till one link slips through your fingers. Now lift the cam sprocket back up into position and line that link you are holding up with the mark on the cam sprocket. Now when you rotate the crank back the other way by one links worth of movement to line up it's timing marks, you will rotate the cam by a half a tooth, and things will all line up.

Apart from cam timing, gearboxes seem to be the second most common problem people have putting bikes together.. They shouldn't, it's so easy to test they are shifting right before you even put the second case on, but... People just seem to prefer to hope it will come right even thought they know somethings not right..haha If you are having to do the work yourself, remember, it's better to backtrack and get it right before you go any further. The further along you are, the least inclined you are going to be to backtrack when you have finally accepted there's a problem. As mechanic I know, we can write off some hours, it's only an hourly wage and I can make that back up, but my reputation, and the customer confidence and trust, that can't be easily won back..

Did the guys that did the work have the whole bike when they did it ? They should/would have test run it surely, and tried the gears ?