Mech

Hi. I looked through the 650 manual and it didn't mention any Limp mode. It shows the switch as being connected to the wiring by two wires only. The manual is in the manuals section.. Is it still needing high revs to get moving, as you mention in your first post ? That doesn't really sound like Limp mode.. Those variable ratio belt drives can be quite temperamental.. They need everything just right on the front and rear pulleys, and the distance between pulleys, or they cause problems.

You need to use a test light and trace the power feed to the key switch and onward. Check power is getting to and through the key switch.

Keep trying...

It sounds like the variable ratio belt drive system is playing up. You aren't mentioning missing or backfiring or cutting out or anything that suggests the engine isn't running fine, and those symptoms could be caused by the bike being stuck in a high ratio.. I'd look there first..

Yeah a spanner on the crank will tell us somethings. If the crank is totally seized then it's probably seized the big end bearing, but if it moves a tiny amount it's likely that that play is the crank moving till the conrod tries to move the piston. Draining the oil and inspecting it often shows something too. Since the spark plug has been hit then it is possible the big end or the gudgeon pin have developed play.

You need to keep posting till you can download the service manual; That tells you what work can be done with the engine in place. If you tell us the year and exactly what model it is, I or someone can check for you.. They come in chain or shaft drive, and with or without electric start, and I wouldn't be surprised if there were kick or pull start versions as well.. We need the suffix of the model number..

Ha.. That is a bummer.. That it's started to work ! I hate that too, all the more since I'm a mechanic. Perhaps now leave it idling and wriggle all the wires everywhere bit by bit hoping to find a short or broken wire that makes the motor die.. Wires mostly only break right where they go into the metal crimped terminal, and they break inside their insulation so you need to use long nosed pliers to gently tug on those ones, and the other place that used to be more common in the past when they used thick wires, was up near the steering head where they flex. Shorts to the frame of course.. anywhere. I'd also check the switches.. The kill in particular is prone to dirty or mud filled contacts. The mud not actually being a dirty contact problem, but when it gets wet it can short enough to cause problems. And thanks for the thanks. It's my pleasure.

Bikes of a certain design get released on different continents in different years, and in any particular year they release different version/spec bikes into different markets as well. Also, in motor vehicles at least, and it may not apply to quads so much, countries have trade deals in which a country will assemble vehicles but as part of the trade deal they want to use some local content, so the country supplies some components they can manufacture in their own country.. So wiring looms, seats or upholstery, starters or generators, paint jobs, carpets.. Stuff like that used to be local sometimes. When we are looking at the service manuals, we need to be sure they do apply to our market or the market the bike was intended for.. before it got re-routed to a different market.. haha. And, Yamaha are the very worst for swapping their electrics around I think anyway, without any of those market changes !..

Well it remains a mystery.. Your VIN says it's a 89 model, and when I look up parts the 89 stator has the two bullet connections. The wiring diagrams suggest that the big-bear FWW(89) might have the right stator, but when I look up parts online none of the BB have the two bullets.. The FWW(89) Big-bear wiring diagram shows what looks like your wiring according to your description.. Whether you should rely on the 89 BB specs is to be ascertained yet.. Good luck, FYI. Yamaha designate models years with the last digit of the suffix.. So the last suffix digit W is for 89, U is 88, T is 87, and 90 is A, 91 is B, 92 is D. The VIN numbers use K is for 89, J is 88, H is 87, and 90 is L, 91 is M, 92 is N. Moto-4 to BigBear.pdf

Yeah I got that, but thanks for clarifying. So it seems you must have the 90 electrics. The Vin year numbering protocol has K for 89 and L for 90. We have to watch out though when looking at yamaha model suffix designations because they use W for 89 and A for 90. It gets confusing. Anyway.. The parts say that from 90 on the cdi and stator gets shared with other Moto-4 and Bigbears. That being the case, and since the stator fits a 91 big bear, this should be the same wiring, and hopefully the specs for diagnosing would be the same. I'll have a look in a 91 bigbear manual later, but if you are downloading(one more post I think), then get the BB as wiell as the Moto-4 manual and have a look. The ignition should be the same, the wiring for the rest of the bike may vary.. not all bikes have brake lights for instance, and the start circuits vary. BigBear350-91.pdf

Frame JY43HPW0*KC000101 Engine 3HP-0000101 Model 1989 YFM350ER W Moto-4 JY43HPW0*LC024101 3HP-0024101 1990 YFM350ER A Moto-4 JY43HPW0*NA049101 3HP-0049101 1992 YFM350ER D Moto-4 JY43HPW0*PA059101 3HP-0059101 1993 YFM350ER E Moto-4 JY43HPW0*RA070101 3HP-0070101 1994 YFM350ER F Moto-4 JY43HPA0*SA080101 3HP-0080101 1995 YFM350ER G Moto-4

Yeah the switch is like the 90 model. So the atv's plug shape and colour should match the stator's, and they should match the wiring diagram in that pdf "output", where the 90 is the ERA. The wire colours should probably match too, but, I have followed along in here when people have used parts with the right plugs but a wire or two different coloured.

Have you checked the wiring ? Check the stator wires have a good connection all the way to the cdi. Check the kill switch or disconnect it. Check the stator resistance readings from the cdi unit. That will confirm their connections are good. If you tell us the history of the bike and the problem it might help..

So only the last supplement in the manual has switches as you describe, shorting to earth to kill. The earlier models had the main switch killing for run and the kill switch operating earth to kill.. I also noticed that the two relays are different.. one NC and the other NO.. If the main switch wasn't original it would cause problems..

The 89-90 model that doesn't have a wiring diagram.. that usually means use the first model in the book, sometimes though it says whether to use the first model the manual is based on, or to use the model supplement before the missing wiring diagram. I was just looking in the main model where all the detailed instructions are for diagnosing the ignition, and it had this diagram.. but look at the switches.. Might be a misprint.. output2.pdf

That cdi unit then has a integrated circuit that takes care of the spark and timing, and the IC also controls the start isolate relay. It monitors the brake lever and the neutral and doesn't let the relay work if it's not satisfied. I'd suspect that one of those two earth wires might be to handle the power for the relay.. Just something they would do on cars;. These yamahas are absolute mongols for changing a lot and in many different ways. The start isolation can work in two different ways in yamaha cdi. In some the voltage from the start button being pushed gets fed into the cdi, and in others the power goes through the cdi and then to the start button and they detect the voltage drop. The reason they want to know when the starter's being used is probably so it can retard the timing for an easier start. The way they detect start in them puts them into two wide categories where there are several options.. It5 always pays to check which way they detect the start signal. Also, the colours of the wires, and the colours and shapes of the plugs have to be completely right before you can be sure the match is correct.. That applies to the wiring diagrams and original parts.. You really need the good manual. In manuals they describe some of those stator cdi charge windings as anti-kickback or some such, and in some stators all the cdi charge and battery charge windings look identical, some have a slight difference in windings and some have one huge winding and the rest small.. Keep posting till you can get the manual In the pdf manual index they say they have a model 87-90 YFM350ER, and it has a wiring diagram,the next model covered is 88-90 and it has a wiring diagram, the next model is the 89-90 model and it doesn't have a wiring diagram, then there's the 90 model and it does have a wiring diagram. They have slight variations in bikes in different markets, and they release/use different spec bikes at different times too.. If you find a service manual that seems perfect in some regards, it's often wrong in some other matter. All the makes are like it, but yamaha ignition systems seem/are particularly prone to differences.

You could try swapping the trigger wires about. Some cdi fire at a certain rising voltage of the trigger's output, and later models fire as the trigger winding's voltage peaks.. at the top of it's voltage wave. Those later ones need to be the right way about too. If that doesn't work you could try swapping the capacitor charging wires about too. Some cdi seem to need a certain number of AC pulses before they will start, or it might be they need to finish charging on a positive wave, I'm not sure why, but it's so. And, you need to try all four possible combinations to be sure you have both windings right for that cdi unit.. And.. to make it more interesting for you, you have extra wires to try I suspect.. Also.. not sure if it applies here but my sons used to be forever swapping cdi and stators etc trying to keep their fleet of two wheelers going, and they found that the manufacturers swapped the position of the keyway in the flywheel sometimes, and, even if the key was right, they sometimes swap the magnetic polarity of the magnets. All that aside, they did mostly get a combination that would work eventually.

Better still.. output.pdf

Try these... output.pdf

Ok. It sounds like you know your way around electricals.. The manual does 87-88, 89-90. It has the diagrams. If it's not in the supplement for your year, then the details/specs/diagram for your model/year are the same as the first model covered.

Also.. I thought that connecting the rear brake lights made the light come on. It also doesn't make sense that connecting the wires would effect the spark, not if it is the brake light. Some models though do have a feature to stop you trying to drive with the handbrake on, and the left handlebar brake lever switch if it's playing up(or if you have the handbrake on), will rev limit the bike at barely above clutch lockup speed. I donated that manual in downloads but I've never read it. haha.. I better go read it..

You should check the resistance value of the stator windings and the trigger/pulse windings; the windings may be ok. A flake of metal, or a finger of rust powder, that bridges the air gap between the flywheel magnets and the winding core, can stop them working. You should check the kill switch too for dirty contacts or rusted spring, and the main switch if it sits out-side getting wet can likely get water into it causing the same problems. The handlebar switches though on most bikes are fairly prone to dirt and water. There's a service manual in here in the manuals section. That will have the4 diagnosis process and all the readings for checking the cdi. They will tell you to check the resistance readings, but they probably wont tell you to check there is actually power coming out of the windings. There are several things that can prevent the windings working properly even though they have continuity and the right resistance. The wires to the cdi can have bad connections too so I'd suggest you check the windings resistance and output at the cdi plug, or, at the plug and down at the engine plug so you can compare the two readings. To check the main charge and cdi charge windings you can use a digital meter but to check for output from the trigger/pulse winding you should buy an old fashioned analog/needle gauge. The needle on the analog gauge will flicker and you will see it has some output and know the flywheel is turning, the winding is bolted on in the right place, there is no build up of metal dust shorting the magnetic field etc.. Most digital gauges don't detect the brief single pulse on the volt range. Doh.. Just reread and noticed you do have the manual and have done the process.. still check for out put though, and do the tests up at the cdi plug.. Wires get dirty connections in plugs or where the terminals crimp onto the wire.

I'd suspect that "auto" is really a variable ratio/diameter set of pulleys and a belt. One of the pulleys will either be moving apart to the shrink the effective pulley diameter, or, not separating when it is meant to be separating, and so causing the high revs and no top speed. The struggling up hill might correct itself if you fix the pulley problem. Does the engine seem to have full power when it accelerates away from a standstill, or perhaps at mid speed it might perhaps to have full power ? If it seems to have full power at some speeds (the speeds the ratio it's stuck in suits), and if it isn't actually missing uphill, then I'd concentrat5e on getting the belt drive cured.

All excellent advice Magnolia..

The trick is Gw, to have a little puff of the stuff yourself, before you get on the bike.. haha