Anyone know about Yamaha atv's?

Streetbu

Streetbu

Royal Smart Person
Supporting Member
May 22, 2011
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Central NY
So being the nice guy I am, I offered to help a friend get his Yamaha Warrior up and running. Hadn't been used in almost 8 years. Carb was nasty like you'd expect. Cleaned it, still wasn't right, ordered a carb kit, put it in, new NGK iridium spark plug, ran like a top. When sitting still. He got it home and finished installing all of the plastics and took it for a ride, it breaks up horribly under load over a certain rpm. Sounds ignition related. Stators at common failures. Just tossed one on. No dice, runs exactly the same. I'm out of ideas. Would any of you guys be able to point me in the right direction?
 
superbon54

superbon54

Master Mechanic
Apr 15, 2014
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I don’t have Yamaha experience, but I’ve been wrenching on carbureted atvs for a long time. Most of the big name oems used mikuni slide carburetors. They work under the same concepts as our car carbs, but execute it in a totally different way. A jet may be plugged or the slide sticking. Also, CDI boxes are a common failure to look at too. Either one could give the condition you state, and those are where I would start.

I’ve got a really good book on slide carb tubing. I’ll dig it out and see if there’s anything that could help.
 
Streetbu

Streetbu

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Supporting Member
May 22, 2011
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Central NY
I'm definitely not an expert, but it sounds ignition related, not fuel. Almost like a rev limiter, or coil breaking up, etc. But not at full speed. Maybe 2000-2500 rpm. and yet is fine not under load.
 
superbon54

superbon54

Master Mechanic
Apr 15, 2014
409
93
Since you’ve got a new plug, check the wire to make sure it’s ok. I had a wire go bad one time and I couldn’t run high rpm at all. Had a CDI box fail once and I couldn’t give more than half throttle or so under load.
 
axisg

axisg

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Jul 17, 2007
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subscribed. Friends kid has a 2000 Arctic Cat 500 with a Suzuki Motor. Idles fine, dies under load unless you are really careful with the throttle. It runs like a scaled cat once it clears up under WOT. New carb, plug, wires, fuel...... Its had me baffled for over a year now
 
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81Regal

Royal Smart Person
Apr 5, 2009
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Terril Iowa
I would say the CDI box also, from my experience they dont like sitting.
 
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Streetbu

Streetbu

Royal Smart Person
Supporting Member
May 22, 2011
1,842
113
Central NY
Well I figured one issue out. It had a parking brake which he removed. There was a parking brake switch included in that. Tied those wires together, now it will stay running in reverse....
 
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