[Robertall]

Hi,

I am unsure what catagory is best, but i thought it would best in here, as it has an engine.

Earlier i got given a Viking lawn mower mb 650 vm, non-runner. The engine was tight, but i took the head off, lagged in it oil, and i worked out that it has been stood for some time, i used an airline to remove the excess oil after turning it over a couple dozen times. I then put the head back on, after cleaning the gasket. It is an old fashioned sidevalve type engine, and with a reusable gasket.

The machine is turning over freely, with some new oil. It wouldn't start. I took a gamble, and put my finger on the end of the spark plug, risking a shock. Had it turned over, and nothing, not even a dribble of spark.

I checked the electrical components, all looked visually fine, a few parts had a bit of corrosion, so i cleaned it and oiled it with duck oil.

It still won't start. It has no spark. I then guessed it could be the spark plug, i took the cap off, the end of the HT lead was rough, i chopped off 5mm of it, and put my finger on the end of the HT lead. And still nothing.

WTF is wrong with this thing...lol....anything i may have missed?

[CurlyBen]

A lot of small engines (and particularly 2 strokes, chainsaws etc.) kill the engine by shorting the plug to ground at the coil. Try and find the coil, if there's a small wire connected to it disconnect it and see if it fires up. If it does, trace the wire and somewhere you'll find a fault. They're really simple, normally not even a proper switch. I've had a few bits of machinery which wouldn't shut down because grass or wood had got into the casing, and the switch is just two plates. It's more common for them to fail open than shut, but not impossible. If that doesn't work, try and disconnect both ends of the HT lead and check for continuity. If that checks out the magneto's probably dead, not too expensive. Check the magnets are still fixed to the fly wheel, normally two of them. These little engines are surprisingly complex - I got a little confused with one of ours recently, until I realised that it's actually got a proper governor as well as the throttle. 2 stroke carbs are pretty intricate too.

[Robertall]

The 2 magnets (are very magnetic), do they need to touch the flywheel, or just be very close? When i took it off they were not touching, and also

I seen that cable, i thought it was part of the circuit, i will disconnect that tonight and try that.

It is a 4 stroke sidevalve engine.

[CurlyBen]

The magnets should be fixed to the flywheel with a small gap to the magneto (coil). They're normally two squares set flush with the edge of the flywheel. They spin with the engine to time and generate the spark.

[Nuffles]

Don't bother risking burning yourself with a spark, simply touch the thread of the spark plug to the head/block and if there's a spark you'll see one. Hold the spark plug with rubber-handled pliers ideally.

[Robertall]

It now has a spark, i put some fuel into the spark plug hole, it fired for around 1 second and then it cut out. It doesn't appear to be drawing fuel from the carb, but at least i know it should run. Thanks for your help