08 600HO RMK shitty fuel mileage - HCS Snowmobile Forums

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Old 08-12-2019, 09:23 PM   #1 (permalink)
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Default 08 600HO RMK shitty fuel mileage

So under normal riding conditions, not hammering it i get about 7 miles per gallon, less when i ride hard. It has the stock setting. 400 mains and the c clip is set on the 2nd from the top. I'm thinking of going to 380's and moving the clip to the top spot. Is that to much at once ?
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Old 08-12-2019, 10:18 PM   #2 (permalink)
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I'd be looking at track tension, wheel bearing condition, chain case gearing, clutching etc. Has it always been low? I could see it being around 10mpg, not much better though. I ran 390s in my 500s and would get around 10. Might be to lean for your 600.
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Old 08-13-2019, 08:41 AM   #3 (permalink)
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Thanks 1fast. the track spins freeley no tension, it is a 2" though. I will check the Chain case. Do you think going to 380 and moving the c clip up to the top is to lean. If i do that I can check the Spark plug wash ever couple miles as i ride to make sure. but the plugs were very dark almost black before. and yes it has always been the low of mileage.
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Old 08-13-2019, 08:58 AM   #4 (permalink)
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Smaller main and moving the needle clip up would make it very lean. Dangerously lean I think. I think the 2" track is most of the problem. What gearing is in it? Too tall and it would lug the engine along. Possibly causing the black plugs. You should be around 2:1 gearing. That would make the cvt more efficient and net better mileage. Although, I don't see it getting a whole lot better.
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Old 08-13-2019, 09:21 AM   #5 (permalink)
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I ran my 600 HO short tracks in the second clip pos., 380 mains, airbox gutted, timing at 28 degrees.

I never hold it wide open across a lake.

I got 12 to 14 mpg's

I put 400's in my customers sleds for a little wiggle room.

Clutching/gearing makes a big difference.
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Old 08-13-2019, 06:57 PM   #6 (permalink)
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Good point, i will check the gearing, i never paid attention to the RPM and speed. I would imagine it it stock gearing though it's an RMK. And start out with just the 380's
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Old 08-13-2019, 10:20 PM   #7 (permalink)
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Don't forget to pressure test your carbs.The viton tips wear on the n/s assembly and the orings leak on the n/s assembly VERY often.I replace tons of them on those sleds with rack carbs.If you run ethanol fuel its worse.
too slow and fastsleddr like this.
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Old 08-14-2019, 08:13 AM   #8 (permalink)
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I wouldn't mess with leaning the needles on a 600 unless at higher than 3k feet elevation or riding near 50 degree temps. We had a guy on a 600 do this years ago riding at sea level, and squeaked his motor while riding a steady 45-50 mph down a river. Those carb n/s o-rings can leak after a few years without realizing its going on. If you run any e10 fuels its worse. Should get around 10 mpg if running hard most of the time.
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Old 08-14-2019, 08:58 AM   #9 (permalink)
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Current Sled(s): 18' Assault Founders, 09 D8SB, 08 600 RMK.
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Quote:
Originally Posted by sleeping_dragon View Post
Don't forget to pressure test your carbs.The viton tips wear on the n/s assembly and the orings leak on the n/s assembly VERY often.I replace tons of them on those sleds with rack carbs.If you run ethanol fuel its worse.
So if i get new needles and the O-ring,( that is the plastic piece in the pic correct) and a carb rebuild kit that should take care of it, not necessarily the gas mileage, but potential leaks, As long as i have it apart i might as well put rebuild kit in. I'v had the sled for 3 years, runs great but it probably has not had a carb rebuild.
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Old 08-14-2019, 08:59 AM   #10 (permalink)
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Current Sled(s): 18' Assault Founders, 09 D8SB, 08 600 RMK.
Previous Sled(s): 03 Pro X 800, 99' XC 700, 94 650 RXL
Location: Prior Lake, Mn.
Favorite Riding Area: Northern Mn. U.P. Wi.
17-18 Mileage: 950 So far
16-17 Mileage: 1250
Age: 53
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Quote:
Originally Posted by too slow View Post
I wouldn't mess with leaning the needles on a 600 unless at higher than 3k feet elevation or riding near 50 degree temps. We had a guy on a 600 do this years ago riding at sea level, and squeaked his motor while riding a steady 45-50 mph down a river. Those carb n/s o-rings can leak after a few years without realizing its going on. If you run any e10 fuels its worse. Should get around 10 mpg if running hard most of the time.
That's what i am gathering. I will start with 380's and a carb rebuild kit.
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