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Thread: Help with my Grizzly 660

  1. #1

    Default Help with my Grizzly 660

    I have a 2004 Grizzly 660. After riding at slow steady speeds in nasty terain that requires 4X4 my gas usually boils (but not always) and when I come to a hill and need to give it some gas it starts to cut out bad. It was so bad this last ride I couldn't climb a hill that my sons 80cc climbed. Usually I'll have to lket it cool down and slowly work myself back and forth up the hill until everything "clears" out and then it will rip up the hill. At first I thought it had to do with incline, but even on a straight stretch under those conditions it will cut out (when I get on the gas). It acts like it's loading up and once I've cleared it out it will be fine for a few more miles. Any ideas?

  2. #2
    Member alaskanmoosehunter's Avatar
    Join Date
    Apr 2007
    Next to my trashy neighbor


    My friends griz did that last year and it's a new machine with power steering. He did some research and found that Yamaha had a recall on this problem. Recalls are for safety of the public and more than likely your machine will have the same recall.

    The dealer fixed the problem and it hasn't happened since. Fuel still gets pretty **** warm though.

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  3. #3
    Join Date
    Dec 2006


    I don't know if your model will be covered for the recall or not but what you need to change is the "Roll-Over Valve". The dealers have them, just be sure it is the "new" one not an old style. It takes about 8 or 10 minutes to change. Really solves the problem. My 700 now has 'quiet gas' and doesn't stall or loose power at all.

  4. #4


    On my 04 660 the culprit has always been mud buildup in the gastank cap/ventline. It plugs up and vacuum locks the tank, next time it does it try loosening the cap and see if it helps. My two cents

  5. #5
    Member IceColdak's Avatar
    Join Date
    Sep 2008
    Anchorage, Alaska


    Its probably the roll over valve--I changed the one out in my 700 Grizz with a small style fuel filter (lawnmower type) and no issues after that. Alot of guys just get rid of that valve.

  6. #6
    Member AKMuddy's Avatar
    Join Date
    Aug 2007
    Palmer, AK


    Although Yamaha did have issues with the newer EFI Grizzlys having a "rollover valve" issue, the old Grizzlys don't have that issue at all. There have been some issues with the 660s "boiling gas". It's not actually boiling from the temp of the fuel but more because the pressure built up in the tank. Yamaha did a "recall" on the early Grizzly 660s (2002-2003) models. Not sure if the 2004s were included because I think Yamaha fixed them before they were released. More likely, the culprit is two separate things. First off, check your fuel tank vent tube. Make sure it is clean and clear on the inside (I would use a pipe cleaner on it). Also make sure it is not twisted in any way. This will most likely cure all your issues but I would go one step further...check behind your radiator and see if it is clogged with dirt, mud, weeds. If you don't spend a lot of time in the water (like I do) you can have issues with the radiators on the Grizzlys getting clogged up from behind. Take a pressure washer and get in there and clean her out. When you are riding and see any decent water hole, get in there and clean off your bike...she will thank you for it!!! Good luck. If that does not fix the issue please let me know. I know these bikes pretty well.

    You can also do a google search for "Grizzly Central Forums"...that is the number one site for Yamaha Grizzly Owners on the internet. Those guys over there know all there is to know about those bikes and they are the ones I have learned the most from. Look me up on there as well...I go by "AKMuddy" on that site too.
    2007 Yamaha Rhino 660
    2007 Yamaha Grizzly 700 SE w/EPS

  7. #7
    Member EagleRiverDee's Avatar
    Join Date
    Apr 2009
    Eagle River


    Quote Originally Posted by AKMuddy View Post
    Although Yamaha did have issues with the newer EFI Grizzlys having a "rollover valve" issue, the old Grizzlys don't have that issue at all. There have been some issues with the 660s "boiling gas". It's not actually boiling from the temp of the fuel but more because the pressure built up in the tank.
    That can happen- you can "boil" liquid at room temperature by drawing it down into vacuum conditions. It's an interesting phenomenon.

    If you're interested in seeing how it works, there is a short video on it here: (click on the one titled "Boiling water at room temperature".)

    It might provide some insight on solving this particular problem.
    "If snowmachiners would adopt the habits of riding one at a time and not parking at the base of avalanche prone slopes, the number of fatalities would likely be whittled by at least a third, if not by half." ~ Jill Fredston, in the book Snowstruck, In The Grip Of Avalanches.

  8. #8
    Member theultrarider's Avatar
    Join Date
    Mar 2009


    I have a Polaris 700 that had pretty much the same issue. Acted like boiled gas and they too had that issue. I line the bottom of the tank with heat tape as well as the fuel lines. It helped, but it would still act as you desribed when working ti hard. This went on for 2-3 years and finally grabbed may buddies rig that is is twin to mine and started swapping parts til I narrowed it down. Long story short, it turned out to be the needle in the carb as well as the brass nozzle that were both worn. Not the needle and seat run by the float, I had already replace them with new, But the needle that goes up and down with the slide and the brass nozzle that it drops into. I put in new ones and it runs GREAT. I also now get better fuel milage than I did even when it was new. It was getting terrible. I am so glad to have finally figured that one out. As the fuel gets warm and pressured it, it would just blow right by there and make the engine run pig rich. Hope this helps somebody.

  9. #9
    Join Date
    Oct 2005


    The issue is that the 660 generates a lot of heat at slow (5mph or less) and heavy load on the engine like hill climbing trailering etc. The side panels don't let the air escape and the heat builds up in the engine compartment. It only happens on mine if it's like 75 or hotter outside. The solution is to just pull the side panels of so the heat can escape. I have a set of side panels that a modified several years ago but using a hole saw and cutting some holes. I ride with those during hot summer rides. My griz is an 02. My buddie Silvertipgriz has installed and aftermarket radiator on his as part of his big bore project and it came with a larger fan. That fan really moves the air out of the engine compartment and he has no problems. Even with a 686 Big Bore. Yup, the problem is nothing more than hot air!


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