Older two strokes and unleaded 95 fuel

[Hagar]

Am posting this for a fellow fisho who has an eighties model Evinrude 90 .

He asked my opinion on whether he needs to run the new lead replacement fuel unleaded 95 or if he could use regular unleaded as it's cheaper . My opinion was that the lead content probably is not the main issue with no valve seats to worry about but the lower octane rating of regular unleaded could be an issue if his older engine has a higher compression ratio than newer outboards . My understanding is that higher compression ratios in older super powered cars prompted the 95 octane unleaded coming out when they canned super fuel .

Has anyone got any info on this from their marine mechanics . What are you guys with older outboards running in them as super is phased out ?

Chris

[Thud]

I'm running an '84 Evinrude on unleaded and have no problems (touch wood)
I also ran an '82 model on unleaded for years before it died.
But that was a gearbox issue.


Cheers

[QldKev]

I've a 1977 55hp evinrude for the past 5/6 years and now my 1977 84 Merc, both run ULP.

[Hagar]

Bump !

Any more fellas ? Spaniard king - any experiences Gary ?

Chris

[Oldyella]

The older OB's were designed to run on 89 octane (USA) which is our 91 octane. This is standard ULP. If you use higher octane or premium, the only benefit for the extra $ is the additive used to help with longer storage of the fuel. You will get no performance benefits under around 100hp. It is recommended to use higher octane fuel on the bigger motors like tho old T.O.P Mercs and VRO's.

[New_fisher]

RD805, I don't understand how there can be power advantages with using a higher octane fuel with larger motors and not with smaller ones - if the octane is high enough to provide a noticable increase in power with the larger engines for example 4-5% then surely there would be a 4-5% increase with all engines? or I could be wrong....

[FNQCairns]

Hi Hagar, to put it in perspective even the highest compression ratio standard outboards run it is still way below vehicle compressions for the same era. I suspect also that the US was using basic unleaded in the year of manufacter of that engine also and they change nothing when exporting engines.

So he should have no problem on octane alone but he migh want to consider getting the timing changed/checked as this was the done thing at the time to account for the lower quality of the fuel overall.
If the mechanic upon reading the timing figure suggests it be retarded for safety sake it may in the end be cheaper to just run the premium and keep the more efficient timing values.

Depending on where he buys his fuel I would almost guarrantee he has bought basic unleaded from Premium/Lrp bowsers. I know I have many times, one of my cars lets me know in no uncertain terms what grade fuel it is running. cheers fnq