davefrombc

Unless you're going to run any accessories for any amount of time with the motor off I can't see any advantage to installing a larger battery.

I know it may be simplistic, but did you try swapping out the spark plug ?.. One friend beat himself up looking for his no spark problem until another asked him if he tried a new plug.. Sometimes it is the simplest things that trip us up. That is on our first check list ever since when there is no spark.

Coolant in the crankcase sounds like a cracked block or head to me; although if the head and block have water passages between them . it could be a head gasket problem. Rings and valve seals will not let coolant into the crankcase , but a bad head gasket or cracked block or head will let pressure and coolant into the crankcase.

OK.. Sounds like you found the problem. Yes , new problem sounds like you got some junk into jet on the carb. If it has been sitting for a long time I'd suggest taking the fuel tank off and putting some marbles in it Close it up and give it good shaking so the marbles knock all the crud loose in the tank and you can rinse it out and clean it .. You may have to replace the fuel valve also. They generally have a screen on them that may have deteriorated, or may have been damaged if you left it in when giving the marble and shaking treatment. Clean the carb, add some fresh gas to a clean tank, and hopefully you are good to go for some fun riding.

Here is the ehow response to an inquiry on the location of the Moto 4 serial number. http://www.ehow.com/how_7552168_identify-yamaha-model-moto-4.html Once you know the year and model of your quad you can search on a service manual for it . In the meantime , I would check out the ignition switch and also check to see if there is a second relay in the circuit that powers the system. If the ignition switch isn't making proper contact , nothing will work. When you jump the starter solenoid , you are bypassing the ignition switch and main power circuit. Does the motor start and run while you have the starter solenoid bypassed and die as soon as you break the bypass? That would indicate the ignition switch or a main system solenoid if used.

I am not familiar with your quad so I can't do any more than guess on those wires. If you bought the quad new , they are likely wires in the standard harness that would go to optional accessories not mounted on your quad . If you bought it used , then I would guess they went to some accessory(s) a previous owner removed .. Either way , if they are taped up and the quads performance has been normal, then they are nothing to worry about .. You might want to trace them to their other ends to see where they go. If they're open at the other ends of them too you may be able to guess what they may have powered, and would know if they might be useful for you to hook up some future accessories.

It sounds to me like a component in the "brain box" is failing. The "No ECM communication" means for some reason there is no proper signal from the " Electronic Control Module". That's one of the "joys" of new fuel injected equipment ..When something goes wrong you need diagnostic equipment to trace it down..... or you do some expensive guessing and swapping components until you hit the one that is at fault.

The same seller is showing what looks like the same carb, advertised as good for both the 2x4 and 4x4, and at the same price. My guess would be the one shown in your link may have jets optimized for the 2x4 model and possibly would result in a lean burn for the 4x4 which may require a little richer mixture for the extra power demand of 4x4 . http://www.ebay.com/itm/Carburetor-For-YAMAHA-BIG-BEAR-350-YFM-350-2x4-4x4-Carb-ATV-1987-1996-YFM350-NEW/361083283109?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D41376%26meid%3D56aec9c352384768921b96d5550b6c93%26pid%3D100005%26rk%3D4%26rkt%3D6%26mehot%3Dpp%26sd%3D191083519513

Not an old member here in the sense of long time on the forum since I just joined last July, but at 73 I've likely got several chronological years over most of the members. Don't call me old though. I can still do everything I did when I was 18........ It just takes longer, I need more help and I hurt a lot more afterwards. I can even remember where I put things... Well some of the time anyway. Got the new rear axle in my Honda Fourtrax 300 FW. I definitely got all the life out of the old one. The splines on the axle and in the hub and the left side were completely worn out to the point the wheel spun free. With the full time 4x4 it really didn't show up until I got in some slippery stuff on a steep grade and one front wheel didn't have much contact. There is no posi on that front axle , so with it without traction and only one rear wheel driving, I went nowhere .. Had to use the winch to get up the bank, and all was fine for the rest of the ride. There's no hesitation now with both rear wheels driving again.

I'd pull the carb and give it a thorough cleaning. The slide might be sticking , or you may have an air leak or jet partially plugged. Your description sounds like it is running lean to me .

Age is only one factor, and it can be the least to worry about . An ATV only a couple of years old can be in terrible shape if used hard and not maintained while one 30 years old can be in excellent shape. I bought my 1991 Honda Fourtrax 300 4x4 used 4 years ago.. The only repair I have had to do to it is replace the rear axle and hubs last week because the splines wore out on them.. That is a very common problem on the older solid axle quads. The motor still has excellent compression and doesn't burn blue. Starts with a quick press on the start button. The transmission and clutch have also bee problem free. Regular oil and filter change, and some grease go a long way keeping the old ones running like new. Newer quads have more bells and whistles, but if they are loaded with electronics they also have more things to break down. It's a lot easier to rebuild a carb than diagnose and service a fuel injection problem for example. Decide what you want , then go look at what fills your bill.. Look at the condition and see if there are service records . Age really is the least of the worries to consider.

There are 2 screws that affect the idle .. The idle air screw and the throttle stop . You adjust the idle air screw to get the best mixture at idle. . When set right , it will have close to the fastest idle, and not stumble when you open the throttle. The throttle idle stop is just that . It sets the minimum throttle opening. That is the one that will set your idle when the idle mixture is right.

OK.. Glad you found the problem. Maybe the admin here can append this thread to the earlier one so there is continuity on it for the next member with a similar problem.

Here is an old thread on much the same issue. His solution is at the end of it. Click on highlighted area to go to the thread.

It might also be the ignition switch itself. If it doesn't make contact , nothing works on most machines.

Everything I searched on came up with a 2000 model too. Searching from that site and it could be a Big Bear, Kodiak or Grizzly.. Yamaha , like all the quad makers makes several models with basically thee same parts but with slightly different badges and accessories. I saved that VIN search site . Hopefully it will help another sometime down the road. When I went to register my Honda , I had trouble with the VIN stamped on the frame .. it took some searching to fine the proper VIN because of the rust and poorly stamped digits. A little searching plus sanding and using a magnifying lass Iwas finally able to get the correct VIN. That's why I ask others to double check theirs. Nothing like 25 years worth of trail riding and corrosion to make some VINs hard to read. Bought my Honda 3 years ago and when the provincial gov't decided we needed to register them and get a tag for them before we could continue to ride the trails and logging roads . Took a lot of frustration to get the proper VIN to register it and get my tag. I don't mind helping others with similar problems .. That's one good thing about being retired . I have time to search and play on the pc . Now if the pensions just paid better .. LOL

Are you certain that vin is correct ? This is an European motorcycle/ atv parts supply company that has a list of Yamaha ATV's codes from 2000 to 2012. Your vin prefixes don't match anything they list .. They do offer to check a vin you send them and reply by e-mail.. They list neither the 5Y4 prefix nor the AH08W model code; so those may be different for North American models. You could try contacting them and see if they can help. https://www.motorcyclespareparts.eu/yamaha-parts/yamaha-model-prefix-atv-quad.aspx I also tried running your VIN on this site and it came up with an unknown http://www.atvstyle.com/atv-vin-number Other decoder sites also said they could not run that VIN

Just a stab in the dark because I don't know your quad or how that shift cable is mounted.... I take it the shift cable pulls on the shift arm for the forward gears and pushes for reverse. If this is the case, maybe there is a support bracket that is not connected, letting the cable and housing flex a bit (in effect shortening it) rather than pushing the arm fully into reverse.

Sticking float , restricted fuel line or plugged vent could all cause those symptoms . Start with checking for a restricted fuel line or plugged vent before tearing into the carb.

I'd check the float level in the carb for a start .. I'm not sure how that carb is jetted, but there is also a possibility there is a little water in the float bowl....just enough that when you agitate it it gets a sip of it and stumbles.. Beyond those guesses I would say it will be a search...loose wire somewhere in the ignition circuit?

Wide open and not in gear does not require anywhere near the fuel flow it does under load. I don't of any other reason it would die out the way you describe if it is not fuel starvation.

Sounds like fuel starvation. Something is restricting the fuel entering the carb. Some carbs have a screen on the carb's fuel inlet and it could be plugged or a pinched or otherwise restricted fuel line would be my guess. For whatever the fuel bowl isn't staying full under high demand.

OK.. I hope it is an easy fix once you find the problem. When you re-assemble things, use some anti-seize on the bolts to prevent them seizing again.

My guess is there is a shorted winding in the winch. Connecting the positive to each terminal without the negative connected should not have caused any current flow. You'll have to pull the motor off and disassemble it to see where the problem is.

Look on the winch motor .. If there are 3 wires on it , one will be the ground and the other two the forward and reverse terminals. Usually the directional terminals are across from one another while the ground terminal is separate. If there are only two terminals 180 degrees apart, Then the winch runs forward and reverse by switching the power and ground terminals. One terminal positive , the other negative, one direction; switch the terminals and motor runs in the opposite direction.