1955 fuel oil ratio

walleyehntr

Cadet
Joined
Feb 5, 2003
Messages
6
what is the minimum fuel oil ratio that i can run in a 1955 evinrude 7.5 fleetwin. the cover has a sticker that is in quarts and gallons, i figured the ratio to be 20:1. this seems like alot of oil.<br />can i run a leaner mixture without causing engine damage? this motor runs rough at idle, could this be caused by too much oil in the gas. i changed all of the ignition components and it runs a little better. but rough at idle. also gunked the carb and installed carb kit
 

rickdb1boat

Supreme Mariner
Joined
Jan 23, 2002
Messages
11,195
Re: 1955 fuel oil ratio

walleyehntr <br />It is recommended that you run a 24:1 Mixture in those old engines, due to the fact that they don't have roller bearing in the crank. Running a leaner mixture will cause premature failure. They were designed to be run on the richer mixture, so you may have other problems causing your rough idle. Run 1 Quart of TCW-3 oil-6 Gallons of gas and try adjusting the carb a little leaner if it has the provision to do so.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: 1955 fuel oil ratio

Hi, Walleyehntr.<br /><br />The 24:1 recommended mix is 6 USG per 1 qt of oil. The typical portable tank holds 6 US gallons, but little more than 5 Imperial Gallons.<br /><br />That makes it seem more like 20:1, but calculated in ounces it is still 24:1.<br /><br />You might be able to smooth the idle by leaning your idle jet a bit.<br /><br />Good luck. :)
 

alcan

Commander
Joined
Dec 14, 2001
Messages
2,505
Re: 1955 fuel oil ratio

Hi Walleye<br /> Yep, to what the others said. Also if your still running the old presure fuel system. You probably have some problems there. Sounds like you may have an air leak. Inspect the o-rings in the connector. One little nick in them and they are shot. Don't toss the conector, they are hard to find and they are not cheep when you do. They can easly be repaired. Make sure you used the correct procedure to adjust the carb. Check the link and sync. The throtle arm that follows the cam on the timer base, has no roller. These sometimes wear a groove. This puts it out of adjustment. Remember 1 whole QUART of oil to six gals of gas. Once you get the thing adjusted properly you will hardly notice the little extra smoke. They will tend to make your stern a little oily. Just cuff your jeans,roll up your sleeves, rub some of that oil in your hair and think fifties. Seriously, enjoy your motor.
 
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