I have noted with interest member's comments in TANSHA on unleaded fuel and gummed up carbs.

Apart from being a vintage Yamaha enthusiast I have spent over 30 years in the garden machinery business and ones trusty old petrol lawnmower has similar problems to ones old bike, ie they are used during the summer months and usually lie idle from halloween to easter. The lawn mower also has other problems, it has a small fuel tank and a gallon of fuel (in a can) often lies around for a year (or more). The mower's fuel tank is also typically attached to a single (thumper) cylinder engine, so the oxidation caused by vibration in a mower is much worse than on a bike.

In the old days we used 2-star fuel as it was the best choice, it disappeared. We still recommended 4-star over the then new unleaded as, although the 4-star was a bit hot for our low-compression engines, it stored better and a mower lying in the shed for 6 winter months had a half chance of starting in the spring.

When unleaded was introduced we began to find starting and carb gumming up problems, in fact we called March/April the "unleaded silly season" as we are inundated with mowers that wouldn't start for that "first spring cut". Often when we drained off the fuel it looked yellow and smelt more like "bats piss" than petrol, usually being at least one year old.

So we talked to the experts, the worlds biggest manufacture of small engines (and the other thing that made Milwaukee famous), Briggs and Stratton USA,

The advice given:
Unleaded is not a problem, AS LONG AS IT IS "FRESH". It does not store well in quantities of less than two gallons, vibration will oxidise the fuel and unleaded will drop in octane in as little as 24 hours, the Butane and Pentane gasses in the fuel will evaporate off and it is these gases that explode and help your mower (or bike) start.

Their solution:
Use your fuel up in less than one month or buy smaller quantities that you can use up quickly. If this is not possible then use their Fuel-Fit stabiliser. At a cost of approx £3.00 for a bottle it containing enough to treat 125 litres of petrol, ie 5ml (approx 10pence) per gallon. If you buy fuel in the autumn, add 15ml per gallon (30 pence worth) and it will stabilise a gallon for approx 2 years.

How does it work?  "Sorry classified"

I have been told by others that it puts a film over the fuel to stop the aforementioned butane and pentane evaporating off, thereby holding the fuel at the octane it left the pump at as long as you put it in the can before you buy fuel, not 2 weeks later.

Briggs also claim that it not only stops gum forming in your carbs but that it will even dissolve gum that is already there. I don't know how it works but it works for me.

All my bikes start first kick even after long lay-ups. Also, you can keep a smaller amount in your tank!! rather than the other conventional advice ie fill your tank (no air to oxidise with and a quantity more than two gallons) which helps a lot but 4 gallons in your garage is an additional fire risk, is it not?

I have used it for years, I even put it into fuel that will be used quickly as a carb cleaning tool, apart from holding the octane level.

I however would never have recommend it to other bikers as i was afraid that they might blame me if there bike engine subsequently failed, so i said nothing,

Someone however told me that a couple of years ago MCN carried an article on Briggs fuel fit advising their readers to visit their friendly lawnmower shop and acquire this 10p a gallon  additive option, rather than some of the other very expensive alternatives.

Any thoughts out there??  I am 50 years old yet I am still young enough to learn from any other VJMC members who can prove me to be talking bull***t here!!

Brian