I bought a new self propelled push mower recently with a Briggs and Stratton engine.....the owner's manual specifically states "Do not use premium fuel". It doesn't say no benefit to premium.....just says "Do not.."

Why would it state it that way?

 

The compression may be too low to run effectively on premium. The higher octane rating indicates its higher resistance to detonating in the combustion chamber. Low compression might not produce enough pressure to allow combustion.

 

Low compression so it is an easy start. So no need for high octane as stated above.

 

And maintenance problems down the road IE high carbon due to non-combustion of a % of fuel. Just put elcheapo regular in it and once a season pour 1/2oz (NOT BOTTLE) of gas treatment in a full tank before it gets winterized (don't forget winterizing it means run it till it runs out of gas, the preceding sentence is for when your using it just before winterizing).

 

Thanks for the replies!!

 

Copied from the web, author unknown. True or not. Maybe it's all about over heating.
Just a note on fuel octane....Small engines are indeed designed to run and operate on regular unleaded pump gas (87 octane) and with the price of gas now a days well.....
Higher octane is meant for higher performance engines usually with higher compression ratio's. Compression causes heat, the higher the compression the higher the heat, lower octane fuels combust at a lower temp and can ignite under compression before the spark plug fires to burn the mixture (pre-ignition, detonation, pinging) Generally air cooled engines are more susceptible to this as engine temp is not regulated
It is my opinion that higher octane fuel does increase performance and burn cleaner, while it wont be noticeable on your push mower while putting around your yard, it may well show up over the life of your mower in the combustion chamber by burning cleaner and more efficiently less deposits fewer problems. If the average homeowner used 10 gallons in a season, the added cost of .10-.15 a gallon.......????