OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Victa Lawn Mower Frames Stale fuel - how/why does it 'go off'?

Hello all.

First post from me on here. It's the beginning of summer (or what passes for it) over here in the UK. I have a 15 year-old Victa AF055 two-stroke rotary mower which used to be very reliable. In recent years it's got progressively more difficult to start - but usually only for the first cut of the season. Once it's been run, it would normally start first-pull for the rest of the summer.

Anyway, for the last couple of years I couldn't start it at all so I took to using an electric mower. I now want to revive the Victa and need some advice.

My first question is about this issue of 'stale fuel'. It was only on reading the owner's manual today that I saw the advice to drain the tank and use fresh fuel at the start of the season. Is this really necessary? What happens to the fuel that causes it to be 'stale'? Is it something to do with it being a two-stroke and having an oil-fuel mixture?

My second question is about the spark. I've tried checking the spark by removing the plug and cranking the engine. There is a spark, but it's very small and yellow. Not the nice big fat blue spark that I would have expected. Is that normal for a Victa with a magneto type ignition system? Is there anything that the DIY home mechanic can do without special tools like flywheel pullers, etc.

Thanks for any advice you can give me.

Mike

Fuel goes stale because, all the highly volatile particles have all evaporated leaving you with fuel that does not burn well at all, think of it like on a hot day and you open your fuel can and you can see the fumes coming out and smell them. Also with two strokes over time the petrol breaks down the lubricating oil and leaves you with a pretty ugly mixture that does not burn cleanly and may well not lubricate your machine properly.

As for your mower, I would be fairly sure that it would be a powertorque engine, but I am not sure what got exported, Bruce would have a better idea than me. Try putting a tiny bit of fresh fuel down the spark plug hole, if it will not fire then, we can go into more detail.

Thanks Joe, I'll give that a try.

Well, a little progress to report...

I replaced the plug with a new one and filled-up with new fuel (with a stabiliser added this time)

It started on the first pull, but only ran for a few seconds and smoked quite a lot. Now it's back to its usual good imitation of a dead lawnmower.

The spark looked better with the new plug, but I'll test it again when it gets dark and I can see the spark a bit more clearly.

The plug seems to get quite wet, although I wouldn't say it was so wet that it wouldn't work.

Any ideas?

Mike

Hmmmmm. I tested the plug in the dark and there was no spark at all. I guess I'll be stripping it down tomorrow to see if I can find out why. If it's a problem with the kill switch it should be easy to fix, but if it's something inside the bowels of the magneto it will be 'interesting'. Bit of a shame considering that it did run for a short time earlier today.

Obviously you need to check the kill switch circuit in the hope that you will find the answer. Because the failure was somewhat progressive, though, you may find the insulation on the wires in the magneto secondary is breaking down, perhaps partly due to long exposure to moisture and repeated freezing, or just long-term chemical changes. I had a Villiers engine on a Supaswift mower that had a problem with magnetos dying of old age, even though it hadn't been frozen very often here in Melbourne. The first mag lasted 25 years, then the second-hand one I fitted lasted another 20. When the second one failed I finally saw reason and asked the city council to take the old Supaswift away - preferably far away. I hated that mower.

Mike has the insulator(the white part centre of the plug) got carbon on it (it should be white not grey).

Unleaded fuel tends to carbon up spark plugs and as we all know carbon carriers electrical current thus the plug shorts out and guess what no spark.

I have been caught a few times with spark and it was a good lesson learnt.

Thanks guys.

Bruce, the original plug had plenty of carbon crud on it, so I bought a new one. The guy at the spares place reckoned the original plug had probably never been replaced. Initially it looked like the spark was much better with the new plug, but now its not showing a spark at all.

I was going to take it apart today, but something else came up, so I'll give it a go tomorrow.

At the moment it's looking like a problem in the ignition somewhere. I have stripped it down once before a few years ago (in an attempt to improve the spark) but seem to remember not being able to get inside the magneto. If it's not the kill switch, then it's going to be the coil, condenser or the HT lead itself, all of which will involve stripping the magneto.

Anyone know if the HT lead is one of those carbon trace ones? You know, the ones where the suppressor is effectively built into the conductive material in the HT lead? From my days of fiddling with car engines, I recall they were an endless source of problems.

Oh well, at least if I take it to bits it'll fit into the dustbin easier

Mike