oil mixing ratios

In my experience with older 2 stroke dirt bikes, I was always told that the factory suggested ratio was determined using oils of that day. with the advancement in oil technology they lubricate better and thus a slightly less rich oil ratio was needed. So my question is what would be the ideal ratio for an old 1976 eska 9.9? the manual says 50:1. but at this ratio, I am getting an excess of smoke and tend to foul plugs sooner than expected. I have probably less than 5 hours on these plugs and already beginning to foul. granted those 5 hours and been over a course of a little more than a year. (dont run it too much). but it seems like maybe the ratio is still a bit rich. can I lean it out a bit without any worries or am I being too picky expecting a 36 year old 2 stroke to run smokeless? maybe just carry a set of plugs and be glad it runs at all.

Re: oil mixing ratios

I also realized that the problem may lie in the jetting. I am in AZ just over 1200 ft elevation what would the proper jet size be for here? and how much elevation change would require rejetting?

Re: oil mixing ratios

Bike engines, locally generated myths and outboards are very, very different topics, jd.

I know of no case in which an outboard maker changed the mix recommendation based on oil "improvements". I don't either.

Two stroke engines make smoke and sometimes foul plugs. If you expect them to behave properly, follow the maker's recommendations. Using synthetic oils (TC-W3 ONLY) will reduce smoke, carbon buildup and fouling, as well as the weight of your purse.

Do not try to outsmart the guys who designed an outboard. You will lose.

Re: oil mixing ratios

Usually, jet size is reduced OVER 2,000 feet elevation. sea level to 2,000 feet take the standard jet size.

Oil is oil, is oil. Roller and needle bearings inside the engine actually need very little to continue to function. AND, a 50-1 ratio is only needed at continuous full throttle.

HOWEVER: If you reduce oil levels in fuel too much, there will not be enough residual inside the engine to prevent corrosion during storage---of which your engine gets a lot (storage). This is something which OMC experienced when they went to 100-1 ratio. Subsequently they went back to 50-1.

Factory levels of oil were determined by metallurgy and engineering of the day, not oils. Older engines with plain bearings needed much more oil than later --to borrow Merc's saying "fully jeweled power"--roller and needle bearing engines.

Re: oil mixing ratios

I would worry if it didn't smoke, but the first question should not be to dispute the factory recommended mix ratio but rather....what plug are you using and what gap setting?.....also can you veryfie you timing set up per factory spec's (very important) and your compression?, that will make the diffrence with your Eska 9.9 in the way it runs and how much it smokes and its tendency to foul plugs. The 9.9 is normally a lean runner having vertually the same spec as a 15hp Eska except for much smaller carb bore and jetting and intake and a little lower compression ratio due to the rings setting lower on the piston. You should also check your thermostat, many 15 & 9.9 Eska's have them removed....this will effect plug fouling.

You should be using the RJ14YC or autolite 86 sparkplug in your 9.9.... not RJ12C, it is to cold but will work with a tendency to foul in cold weather