OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Reel-Type Mowers Fuel Additive

Gday guy's
I was just wondering what you blokes use for led Replacement for the fuel in the old motors if just flash lube I was thinking of using a cap full or two of Castrol r mixed to about four litres of 98 octane in the scott bonnar cheers

for me i have never bothered using an additive . just sometimes use leftover 2stroke in a fourstroke hahaha .never really seen the need as other problem arise before VSR happens .

my thoughts but im sure they are wrong

Premium unleaded and additives are a waste of time and money in a lawnmower, the only reason I would put 98 in one is if I couldnt get my hands on non ethanol fuel. I drove a holden 202 on straight ULP for close to 10 years and when the head was removed, the wear was marginal on the valve seats but not that bad, especially considering I was doing on average 500km a week.

same here and it was my vccomm hahaha was duel fuel and bottom end let go 1st , head was still sort of good with 350000 on it

My vk ended up cracking the crown off no 1 cylinder and putting the conrod out the side of the block, the head was still good though, it went on the replacement engine!

Had a vc once, never finished it, still have a v8 vb sl.e, had a vh 5.0L ex chaser (awesome car shouldnt have sold it) and multiples of every model in between as parts cars or paddock bashers.

Anyway back on topic, there is one perk of premium fuel, it does seem to last a little longer before going stale, the fuel in my r33 was still reasonable after sitting since 2008 (and unfortunately it has to run the expensive juice) my lawn equipment is used weekly at minimum so the fuel doesnt get a chance to go off.

G'day folks,

Gotta agree with Joe and vccomm. If no other reason than that I'm tight and lazy
A bit of jungle juice of your choosing won't hurt.

But to be a bit more technical, did Honda or B&S (for example) change their valve, guide or seat specs when we-all went to unleaded?

All I add is B&S fuel stabilizer with regular 91 Ron unleaded

I only use 98 in my motorcycles the blended fuel gums up the pilot jet with white goop in the old amals which is bugger of a job to fix and the cheap lawn mower I bought years ago is addicted to it and won't run on anything else.

G'day folks,
91 RON petrol is all that garden machine engines need; they really won't run any better on higher grade petrol. That said, 91 does go stale much quicker than the Premium grades, in my experience. Just avoid all E10 [ethanol blend] fuels!

For machines that are idle for extended periods, it can be worthwhile using either 95 Premium fuel, or fuel stabilizer additive, to avoid staling and gum formation problems. That's why I use 95. In some areas, it can be difficult to find non-E10 91, too.

BTW, 98 RON and above grades are not intended for carburetted engines. They are intended for, and best used in, fuel-injected engines with closed-loop engine management systems. That is, those with both Exhaust Gas Oxygen and Knock Detector sensors. The physical properties of these fuels may differ somewhat from lower-octane fuels; i.e. such things as density, viscosity and surface tension - which all affect the actual air/fuel mixture ratio of a carby. These fuels are known to cause mixture issues in some carburetted motorcycle engines, but of course these are much higher tech than OPE engines.


Well, B&S didn't, because their engines have long used hardened valve seat inserts anyway. Same as all other aluminium four-stroke engines I've encountered.

From Section 1, dated November 1976, of the 1981 edition of Briggs' 'Service and Repair Instructions' manual:

So even back then, B&S engines were OK with unleaded fuels.

Briggs did then offer Stellite exhaust valve seat inserts, and Stellite faced exhaust valves, as retrofit parts. But these were intended for engines operated at constant speed/load for extended periods, which is hard on these bits.