20:1 vs. 40:1 gas/oil mixture - ArcticChat.com - Arctic Cat Forum

Old 12-03-2010, 09:22 AM   #1
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20:1 vs. 40:1 gas/oil mixture

Since I'm fairly new to vintage sleds, less than one year, I've been researching and seeking opinions on the recommended gas/oil ratio for sleds originally spec'd at 20:1. I believe the statement that oils are better today than 40 years ago. From some of the feedback I've received and from what I've read, the consensus is 40:1. What I"m looking for is hard evidence to support this ratio. Has any one taken apart an engine and examined the bearings, pistons and cylinders after running 40:1 for an extended period? Some say, running 20:1 causes more plug fouling and carbon buildup but with today's oils being formulated better, this is less likely to happen compared to 40 years ago. I'm just looking for some evidence to support the 40:1 ratio and why I shouldn't mix 20:1.

Any feedback would be greatly appreciated.

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Old 12-03-2010, 12:34 PM   #2
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Without having a testing lab at your disposal, you're gonna have to rely on the opinions/experiences of others. Is your motor original, high/low mileage, rebuilt? All my premix motors get 40 to 50:1 synthetic. Never a problem. I'd say mix a tank of 20:1 and run it. Then try a tank of 40:1. Next tank try a synthetic oil. See what you like best as far as smoke, fouling, and cost. Only you can tell what's best for you...............
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Old 12-03-2010, 06:40 PM   #3
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I'm not too familiar with the older Cat motors...my old stuff is mostly Doo with a Rupp and Bolens in the mix.
In 1972, Doo spec'd 20:1 ratio for their sleds and in 1973 they changed it to 40:1. There were no changes made to the engines, but Doo did come out with a new oil formulation in '73.

I've been using 40:1 in all my old sleds using Doo's current semi-synthetic oil with no problems.
Not sure how directly this applies to the older Cat motors but just offering up the info to "yellow" the waters.
If I find a nice older Cat to restore, I'm sure I'll stick with 40:1 like I run in all my older sleds.
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Old 12-03-2010, 08:07 PM   #4
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I contacted one of the oil manufacturers a while ago and asked them if there was any benefit to running a mix that was richer than their recommended 50:1 and they said there is No benefit at all. Maybe all manufacturers would not feel that strongly about their product but Amsoil did...a premium synthetic. The quality of the oil is really the bottom line on the mix ratio.

AMSOIL - HP Injector Synthetic 2-Cycle Oil (HPI)
AMSOIL Testimonial - Practice Sled Survives on AMSOIL
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Old 12-04-2010, 07:40 AM   #5
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I tend to simplify this whole oil/fuel mixture debate like this: Spark plugs are cheaper than pistons and cylinders, so if in doubt, give it a little extra oil!

Seriously, I run all my my vintage sleds with a 32/1 mix of Klotz Snowmobile Oil and super unleaded for trail riding, and 110 octane Sunoco race fuel for racing. With a 20/1 mix I seem to get a lot of smoke out the exhaust, which tells me that I'm over-oiled. 32/1 gets rid of the smoke, so that's what I run. 40/1 or even 50/1 will probably work OK, but my feeling is as scarce as engine parts are for these vintage machines I'd rather give it a little more oil just to lubricate things a little better.

Nothing scientific here - just some good ol' backyard engineering! LOL!

PS: Bindernut - are you referring to CORNBINDERS (IH) by any chance? If you are then we need to talk!
I used to race with hex clutches....
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Old 12-12-2010, 02:38 PM   #6
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I went through this debate myself and settled on 32:1. Seemed like a good compromise between excess smoking and to lean a mix for the old 440 motors in my Cheetahs.
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