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Listerjag

Air cooled oil/fuel ratio

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What would be advise re oil fuel ratio with synthetic oil for my Ossa 250 MAR please?

Alistair

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If you end up running say 50:1 then you may need to allow for the richer mixture ie: more fuel : air.

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Thanks for your reply. So if I am running 80:1 with present jetting I would need smaller main jet?

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  • More oil = better piston sealing = more torque i run 30/1 Putoline MX5 in my Bantam back in the day my Maico 125 road race ran 16/1 Castrol R40 got 2nd fastest through the TT speed trap.  Be careful what oil you use some of the latest oils are designed for water-cooled engines  running at 60c air cooled engines run a lot hotter the max temperature i have found on the exhaust port on my Bantam is 180c. 
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Thanks, I hadn’t considered the ring sealing. I’ll see what’s available oil wise around here. 

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I mix 40-1 full synthetic in my Ossa MAR 250,

I did originally use 50-1 , but the bike seems to run better and less hot at 40-1

just my opinion , and you will get people swearing by 80-1, 100-1 etc. 

as well as ring sealing , the oil can absorb some heat as it passes through the engine , and most importantly - bearing lubrication ,

some old 2 strokes have bearings that are only just up to the job, so less oil could be the last thing they need

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