My first post. Hope this is the correct section to post this question.
I've recently gotten hold of a old suffolk punch petrol lawnmower. Was running ok and was looking forward to using in on my lawn.
Pulled it out of the shed at the weekend and thought i'd give it a good clean for the season. I decided the best thing to do would be to spray the engine, in fact the entire mower, in enginer degreaser, leave it running for a while then pressure wash it. On reflection probably not the best idea. The old saying goes "if it's not broken, dont mend it!"
Not long after i'd started pressure washing, the mower cut out and now has about as much life in it as a dodo!! There is just no spark at the plug.
I had assumed that water must have gotten into the ignition system and hoped that if i left it for a few days it would dry out and everything would be fine and dandy. But no! Three days later and still nothing.
Can anyone help? Do you think i have broken anything or do you think it is still simply damp and needs more time to dry out? Is there anything i can do to try and solve the problem or help dry it out? I have read about megneto coil but not sure what this is?
I'd start at plug and work back. Use one from car and see if plug is ok (Unless you have diesel). Has the lead been damaged/dislodged? If you start getting into the main gubbings of the engine, personally I'd bin it. You can get a 4 stroke for £99 nowdays. I got a large self propelled with Briggs and Stratton engine and clutch online for £119. (Can't remember the site off hand)...Bargain.
Can I ask the knowledgable folk here - why dont you get a diesel lawnmower?
Thanks again for you response. I can see logic in starting at plug. But dont think it is plug as i didn't pressure was top of engine or anywhere near the plug. I can't see the entire lead as is goes through a hole into the casing and not quite worked out how to get to it yet. Yeah could replace it but its a bit of a challenge now and i want to get it running again. I bit of a project i guess!!
Too much compression to be able to start with a hand pull ? Need for a glow plug to preheat the fuel mixture to stand any chance of getting it going ? Need for a high pressure fuel injector pump ? Low compression petrol engine with simple carb and magneto-fired spark plug, is simpler all round, requiring no external power source, and no fuel pump. Easily got going with a simple hand-pull recoil starter.
I think this is likeliest. Water and HT electrics (particularly on old machines) don't mix well. I've heard of people using a low oven to really dry out magnetos.
Possibly a bit extreme but if you can expose the magneto and get some warm dry air into it, it can't do any harm.
Wet has got in (pressure washing engines is not a good idea, water gets in...) you need to strip it down as much as you can and dry everything. The ignition module is probably a sealed unit take it off, dry it and put in the airing cupboard for a few days.
Are you sure you have no spark not a carb or fuel tank full of water? Water sinks under fuel amd fuel is picked up from the bottom of the tank.
You have a decompression lever to release the compression. You pull several times to spin the engine up on the fly wheel the release the lever. There is enough momentum to take it through compression and provided the engine is in reasonable condition it will fire.
Not on my small single cylinder diesel gen set. From cold it's as rough as old boots for 10 seconds or so producing clouds of white smoke from unburnt fuel but soon picks up and runs up to speed.
Driven off the camshaft not a problem.
Petrol might be a bit simpler but a diesel doesn't need external power and a 4 stroke petrol as in lawnmower does have a fuel pump to lift the fuel from the tank, built into the tank/carb unit on my B&S.
Never had a lawnmower with a lift pump before. All mine have had the tank above the engine. A lot simpler!
I think the main reason for the absence of diesel lawnmowers is weight & cost. A small diesel engine with the same power output would weight considerably more.
I don't doubt that small diesels are out there on things like generator sets, but they are not particularly suited to use on a lawnmower, for the reasons that I suggested. Key to getting one to start, is the heavy flywheel and valve lifter, neither of which are particularly conducive to the thing being able to be started and pushed, in the case of a non self-propelled type, for someone of a smaller stature, such as the wife ... ;-)
Also, in good condition or not, I'm willing to bet that the thing can still be a bitch to start on a cold day. Witness what little diesels like the Peugeot noddy cars are like when the glowplugs have failed, even with the help of an electric starter - it used to take the lad across the road fully five minutes of almost continuous cranking to get his going, before he got it fixed.
For a standard Qualcast type application, the low revving power of a diesel is not what is ideally required. Easy-start high revs is what is required.
As far as the high pressure fuel pump being driven off the camshaft, that is not really the issue. It still needs input power, as it doesn't get the power to operate for free from the camshaft, so that is additional starting energy that has to be provided by your arm.
Over the years, I have had several cylinder and horizontal rotary petrol mowers, in both self propelled and push variations, and they have all been gravity fed for fuel, with the tank being mounted either up on the handlebar assembll or, in the case of the rotary that I currently have, directly on top of the engine, so no fuel pump of any description being required.
Mowers are normally magneto, which is just a magnet on the flywheel whizzing past a coil, so no contacts anywhere.
OP is fairly likely to get lucky just by drying it out. 2 or 3 days in the shed for a semi-enclosed device is nowhere near enough. Expose it and let it sit a week indoors. If thats impractical, put a warm air blower on it for a couple of days - be sure not to overheat anything though.
Thanks for the responses guys Agreed, i'll not be pressure washing again. It is clean though!! Will try and access the electrinic ignition module and get it dried out. Problem is that it is located behind the flywheel. Not sure how to remove that. Difficult to remove the nut in the middle as the whole thing simply spins around. Any tips? Ta
The magneto fired ones that I've owned have still had points. Accessible through a hole in the flywheel, normally covered by a plastic insert. One Qualcast that I owned needed the points to be cleaned every year before first use, as the contact surface oxidised from the non-use over the winter period. I guess that the points are there to ensure that the 'charge' - for want of a better word - that is built up in the coil's core as a result of the magnet's passing, is 'released' to the plug via the HT section of the winding, at exactly it's peak, timed to be just before the piston's TDC
the mower engines with points are ancient, villiers and that kind of stuff,
nowadays the spart is generated very simply, magnet set in the fly wheel edge, and a coil mounted close to the flywheel, as the magnet spins past the coil, it induces a current in the low tension coil, when the magnet moves past it, the current is stopped and it fires the spark plug from the HT part of the coil, it's a nice simple all in one unit, better known as a CDI unit i believe.
you shut the engine down by shorting a wire out, are you sure your pressure washing hasnt blasted some insulation off a wire and it's now shorting to earth? or something like that,
basicaly there will be 2 wires from the coil, big fat one to the plug and a thin one, that will go to the stop switch, some mowers the stop switch is built into the throttle, push the throttle lever pash slow and it will make a contact that shorts the stop wire to ground, this contaft is usually part of the throttle linkage at the carb.
the earleir sufold punch (before qualcast took over) has a metal tag over the plug, you pushed that down to contact the ht connection to the plug thus shorting the spark out.
BTW, re: the small engine diesels, they dont need a glow plug, they are direct injection, cars like peugeots use indirect injection engines, hence the need for glow plugs,
with a direct injection engine, it just needs the cold start advance to fire in freezing conditions, this is usually automatic but could be a lever on a small gennerator type engine, and for a pull start, a compression release lever is fitted,
There's nowt hard about starting a pull start diesel engine, slightly different to a petrol engine, but they are usually fitted to long run generators where fuel usage is a concern, for a similar sized generator, the diesel engined one will easily use half the fuel of a petrol engined one, also they run at a lower speed, so are quieter, and last a lot longer.
Then engine in my motorhome is a direct injection (iveco turbodaily 2.8) it has a thermostarter, which is an glow plug injector, it's heated up and diesel is pumped through the plug, the resulting hot fuel is atomized into the inlet manifold, it's fed with fuel from the spill rail of the injectors, so no extra pump is needed or owt,
it's totaly automatic in use, will come on when the engine temp is below freezing, i've camped on the top of a mountian in switzerland in november, where at night the outside temps dropped to minus 10, at 09:30 the next morning, i just turned the key straight to start as usual and she fired right up,
Well, it can do. The primary winding current still has to be switched at the appropriate time. This can still be done by a set of points triggering a simple transistor switch. Back in the day, this used to be known as 'transistor assisted ignition'. It eliminated burn at the contact face, so in theory, the points lasted electrically for ever, with less need for adjustment. Some simple 'electronic' ignition systems use an ancilliary pickup winding, positioned such that it produces a pulse at the appropriate firing time, as the primary magnet whizzes past. This pulse is then used to drive the primary coil switch, which again may be as simple as a transistor. Full blown electronic ignition uses a system known as capacitive discharge, where a high voltage pulse is placed across the primary winding at the appropriate time. This makes the coil 'ring' for several cycles. As far as I know, this type of ignition is not employed in magneto systems, due to the fact that there is usually an inverter to produce the high voltage for the primary pulse, and this requires an external power source to operate. I could be wrong there though. I haven't read the whole article and its follow up on the kart engine magneto systems, but it probably tells you somewhere in the text, all about electronics as adapted to work with this ignition scheme.
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