2005 - 660 carburator problem need advise - Yamaha Grizzly ATV Forum
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post #1 of 4 Old 08-30-2010, 12:53 PM Thread Starter
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2005 - 660 carburator problem need advise

3 yrs ago I started having problems with gas getting into the oil (1000 klm.) Had it back to the dealer several times. When slowing down after a steady speed of 60 klm/hr on level ground it backfires. Dealer put new needle & seat Assembly in last month. Gas still getting into the oil making the oil 1/4" higher on the dip stick with only an hours use. However it sat overnight then used the next day so possibly the gas leaked into the oil at that point. Backfire still occurring after a steady speed when the throttle is released and the quad is slowing down.
When transporting the quad in truck the gas is turned off and the motor left running until the engine quits.
Dealers service manager has no idea what is causing the problem. The quad idles correctly and it appears that too much gas is getting by somewhere...Into the oil and into the muffler system causing a backfire.

Any ideas would be appreciated.
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post #2 of 4 Old 08-30-2010, 02:09 PM
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A new needle and seat should have fixed the problem. I would check the needle and seat again for debris/trash. Is there a fuel filter installed between the fuel shut off and the carb. If not, put one in. Did the dealer check the float level? This could cause the problem also, and if float level is too high could be why it's back firing (running rich). Shutting off the fuel petcock when it's parked (and when transporting) should solve the problem also, unless the petcock seals are bad. Check that the petcock is not leaking fuel by removing fuel line at the carb and closing the petcock - no fuel should come out with the petcock shut off. Always shut the petcock off when storing the bike between rides. Fuel leaking into cylinder then into crankcase is a common problem on the 660 when the needle and seat are bad or trash gets caught in the needle/seat. For that reason alone always shut off the fuel when not using the bike.

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post #3 of 4 Old 09-01-2010, 11:24 PM
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I think AZ08Grizz has pretty much nailed it. The gas in the oil is almost certainly due to a needle not completely seating into the seat when it's shut down. Even with a new top end you still have the ring gaps and the fuel will slowly dribble down into the crankcase. When I brought home my used and abused 600 and began doing the restoration. I found that there was literally more gas than oil in the engines bottom end. I'd get a rebuild kit for the carb, probably cheaper than just ordering a needle and seat from your local Yamaha stealer and also go to cheapcycleparts.com or the like and get a new gasket and the internal parts to rebuild the petcock that way you'll be double sure it's not leaking fuel into the carb and the engine when not in use. As far as fuel in the muffler if it had the much extra fuel when running, if it ran at all you should be seeing dark smoke. Did they actually see fuel in the exhaust or just assume that from the backfiring? Backfiring in my experience, not the word of God, is more common when an engine is running lean or the timing is off. I'd do the rebuild of the carb and make sure it's squeaky clean and the float height is set to factory spec as well as the pilot jet screw and see how it runs after that. And as mentioned make sure you have a good fuel filter in between the tank and carb. Good luck and post back your findings.

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post #4 of 4 Old 09-02-2010, 12:44 AM
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There's a vacuum chamber tube that "T"s out and venture to heavens know where. I'm wondering is it possible that someone has accidently swapped and carb vacuum line for a crank case breather line. Consult your workshop manual for a schematic as that may be the cause. I can't see why and engine would run well and still fill a crankcase with fuel. Surely it would run really rich and stink for you to notice such a rich mixture due to needle/seat fault. Even then there's a carb bowl overlow tube that would release the fuel onto the ground not down to the crancase.
I'm sorry .... I don't buy the needle and seat argument at all.

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