sebringwarrior

2003 Yamaha Warrior 350 - Valve Issues

30 posts in this topic

I have a 350 warrior that is experiencing fuel/air vapor blowback out of the air intake side of the carburetor followed by back fireing, powerloss and flames shooting out the back of the carb. Does anyone know what could be causing this???

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could be valves or it might be rings. bad rings will have the crankcase build up pressure and the only way to escape is thru the carb. that might explain the power loss too.

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It has a fresh set of rings and jug bored to match piston. One mechanic suggested loosening the valve adjustment to close intake valve longer??? It doesn't burn any oil and the plug burns with great carbon build up. So I don't think it could be rings, but I am open to any suggestions. You got anything else? Thanks!

Edited by sebringwarrior
addition

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Hmmm??? I don't see how that can cause back pressure out of the carburetor, but I will check that out, Thanks. I am leaning toward a bent valve or tired valve springs becuase the cylinder just isnt taking all the fuel/air that the carb is throwing at it and it should cuz the exhaust chamber has a major port and polish and the thing tachs up like crazy?! This is frustrating!!!! :o

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Who did the porting? The pressure has to go somewhere from the crankcase.

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I ported it and it is real clean and smooth. I built racing motors for Yamaha Marine. (Two Strokes No Valves) I don't see how the crank case breather could be clogged but I will check it. My buddy is a Mecanical Engineer and he is saying "Valve adjustment or bent valve or valve spring"

I thought I rounded out the cam but he says it wouldn't even run. It is some kind of Valve timing issue cuz the fuel that the carb is throwing just aint goin into the chamber and is spittin fuel vapor out of the air intake side of the carb. So instead of having all suction, it is spitting back.

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Seems like you would remember if you "rounded" the camshaft or not. It wouldn't run anyway. IMO, the problem is in your head. Wether it's the porting, the valves, not sure.

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I would have to agree with you! I don't think it's the porting cuz it tachs up way faaster than used to just like a could porting will do and it was doing it before the port and polish even with the fuel vapor backlash deal. I am goin to adjust the valves again first, if that don't work I will pull the head and go through it. Thanx alot! ;)

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And when I say "rounded the cam lobe" I mean wore it down so the valve doesn't open as much as it should and opens and closes too quickly. It loses duration.

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i just sold a warrior really cheap because it wasnt running right kept cutting out and backfiring. it ended up being that the valves were to tight. should try that first.

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Thanx for all the input. I pulled the head today and found that the intake valve was leaking like a civ and wasn't seating. I took it to my Machinist this morning! ;)

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You guys are real funny. Fact is that I will bet that you can't name another single ATV that has been reproduced for over 20 years without any changes. They kept makin them cuz they work!

The Valve leaked cuz the beast vibrated a carburetor to bits and a chunk of metal got sucked into the intake boogerin up the valve. Considering what it went through the damage was rather minor.

That old warrior beefed up the way she is spanks them 400 ex's like they are Tonka toys and then takes me Huntin all night and drags 350lbs hogs back from the woods like pullin one of them raptors around! Very easily! Hahahaha

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glad you got it all figured out sebringwarrior !!

i've only owned yamahas for the last 4 years and i can't say anything bad about them at all. my first atv's were honda and i have no problems with ever owning another one either. i am really not prejudiced against any atv brand, they're all fun !!

and speaking of fun, my post a little while ago was just the continuing funny rivalry mario and i have going. :laugh:

i have a slight advantage sometimes because i am on a pc and mario is on his phone. all good !!

:cheers2c: mario !!

Edited by oxidized_black

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No worries. It's all in good fun. I have had all types of ATV's and the Warrior has been the most all around reliable, versatile, comfortable, fast and easy to fix ATV that I have ever had. I had one back in 89 when it was the fastest ATV money could buy and all these years later I have another one and love it. It's cheap and easy to fix and because of thier production run, parts are everywhere!

I live on a famous mudhole in Florida "Northern" Sebring, FL and we run ATV's all the time. The Warrior really does eat those new 400ex's up, and nothing short of a 450r or a Predator 525 can hang with it in the scrub trails. And no mater how I beat on it, it has never left me stuck out in the woods!

That's what I call a great ATV. Go Team Yamaha!

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Just so you know Sebring, I own two Yamaha atvs and one Honda. All air cooled and all reliable.

Me and Oxy agree to disagree on brands but agree that every atv even ones that dont start are fun

:D

Sent from my SGH-T959V using Xparent Blue Tapatalk

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Agreed! ;) And.....even with no valve compression the Warrior ran fine until you goosed it. I can't wait to ride it after the new valve job!!! Warrriorr! Come Out And Playyyyeee! ;)

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