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I think that's probably a 1989. My data says so and Babbits agree.. Have a look here and see if it all looks like your bike.. https://www.babbittsonline.com/oemparts/l/yam/5003893df870021f60a0a008/1989-moto-4-yfm350erw-parts

This looks like a fair price.. https://www.heavy-equipmentmanual.com/products/1987-1990-yamaha-yfm350er-moto-4-atv-workshop-service-repair-manual

You may be right about the Moto 4 flaps being on the Big Bear, but what makes me think its a Moto 4 is the way the front fender wraps around the gas tank and the seat comes up and over that, the Big Bear didnt do that. Is it 2 wheel drive or 4 wheel Drive, all the Big Bears of that era were 4 wheel drive only.

Good thoughts. I just picked the quad up and drained crankcase. I'll replace oil pump and try again. Thanks for everyone's help!

My thought was it's so full, it's sucking it back up in the cylinder. I don't have fuel or oil line connected, yet oil is still filling the cylinder to the point it won't turn over because of high compression. Oil also continues to leak out of exhaust port. After sitting a couple years, all the 2 cycle oil was gone from tank. It filled the entire carburator including bowl. I'm assuming the rest drained into crankcase. I just don't see any fill, drain or level ports to confirm.

thanks, im hoping that it will last me a while even though it was only 500$

Nice little rides, i think i like the Polaris the best.

The flaps all say MOTO 4 embossed. Maybe hard to see in the photos. I am/was not sure if that was separate from a Big Bear, etc, or in addition to the model #. Has someone done a document explaining the differences? E.g. will a wiring harness for any 1990 YFM350 work on a MOTO 4? I'll ring a stealership next and try to get the harness part # out of the guy.

It appears to be a Moto 4. I had the same trouble with their codes on my 400, YFM 400 can be Big Bear or Kodiak the letters after tells you more.

I havent tried premium instead of Non Ethynol maybe it s better, just as cheap, the non ethynol here only comes in one grade i think its 89.

Those are great machines good luck good luck with it.

I have had this happen before on a 2 stroke scooter, it had been sitting for 10 plus years, it did the same as you describe lock up engine, took me forever to get all that 2 stroke oil out of the crankcase, and it still fowled 2 or 3 plugs before i got it right. I took the hoses all off and drained the oil tank, ran it on premix. Couldnt really disable the oil pump without tearing the engine down it ran off the crankshaft, and was not really on my high priority list, After deleting the oil supply i realized that this pump wasnt going to pump very long without oil and it was always turning when ever the engine was running. So hooked the oil back up to the pump, but instead of rounting into the carb i routed it back into the oil tank. Didnt work well because oil was not getting into the crankcase VIA the carb it was from a bad seal at the oil pump. So my recommendation after all this howee is to replace the oil pump seal or pump itself, or dont store it with a full tank of oil.

VinDecoderz says it's a YFM350 (Moto4 350) trim YFM350ER Is that a Big Bear? Or a Moto 4? Or are they the same thing? I've google'd around for information, and was able to find a (czech board in english) that had a Yamaha service manual for the YFM350X series, LIT-11616-YM-37. The 'Warrior' type. I'm trying to get something more accurate. I'm not sure which manual I need. Pictures included in this post. I'm also looking to get a wiring harness for it.

Thanks for the tip

Just got into ATV riding just last week, never had much money so i couldnt afford to buy anthing, so now at the age of 34 i just bought a 1987 suzuki quadrunner 300 for 500$ took it out a few times and what a rush of excitement to go through that first mudhole haha!

Like you i am a late bloomer when it comes to toys im 34 now and never really had any money, i bought my first quad a few weeks ago, a 1987 suzuki quadrunner, only paid 500$ for it runs and drives, but he said it has a bad oil leak, i brought it home and drained about 3L of oil out before it went down on the sight glass lol

yeah i fix and flip old lawnmowers as a side job and there is lots of mowers i get that some of the carburetors are destroyed from the leftover ethanol after the gas evaporates from using regular gas

yeah it looks like some of these site could use some participation, i was on another suzuki forum and there was dead threads right from the get go from years, it sure is hard to find a manual for a 1987 quadrunner lol

I would only clean the sheaves with warm soapy water with a scotch brite pad no lube on the sheave itself just on the part that lets it expand and contract and i use thin oil no grease WD 40 would work but i generally use a very thin motor oil.

I only use premium 93 in my cars, quad, and small engines stuff. Once in while I'll go fo mid grade in my car if price is high. I use low-grade when I rent a car...🤫

All to encourage participation 😉 Almost there. For anyone else, there's always the option of just going for a premium membership to bypass this rule... Visit https://www.quadcrazy.com/subscriptions

i always try and use the oem parts the cheap amazon ones are junk

yeah same with me you need to do 10 posts if you are a new member to be able to download anything\

i only use premium fuel i think thats 93 here in canada

good morning!