you chaps helped me with mine a year ago and its still running strong.

https://singletrackworld.com/forum/topic/lawnmower-petrol-engine-fix-it-or-buy-new/

the problem then was it kept nearly cutting out when mowing and a good service cured it with your help.  my mates mower wont start at all and he thinks its because hes left fuel in it since last year and its probably crudded up the engine.  if anyone knows their mowers its a Sanli LSP46.  a service kit containing just a plug and filter i think are about £20 on either amazon or ebay.  do you think thats likely to cure a non-starter or should we be looking at other bits to change/clean?  or…… is it likely to cost more to fix than buy another second hand jobbie?

thanks

You could try that as it likely requires a service, but I would be looking at cleaning the carb and fitting a new gasket there and look at the fuel line. Is the fuel left in the tank relatively clear? Can you see the bottom of the tank?

Be very careful around petrol and sparks, if you’re not sure, don’t try this at home…

The safe way… Tester link
Less safe…Spark plug out, connected to the HT lead and and resting on the cylinder head.
Is there a spark when you try to start it?

A couple of drops of fuel through the spark plug hole, replace the spark plug. It should (at least attempt to) start

I suspect the carburettor will be gummed up if it’s had fuel sitting in it. I had a similar issue with my karcher pressure washer that had been left with fuel sitting in it. Giving the carb a good clean, a new spark plug and an oil change sorted it out. Just took some time, a can of carb cleaner, spark plug & some oil.

As above pretty much – take the air cleaner off, spray some carb cleaner over the carb and into the intake – reassemble and hopefully ok.  Oh and check they haven’t turned the fuel feed off!

I’d take the plug out, give it a clean, spray some quick start into the cylinder replace plug and lead and go from there. Sorts out our mower. I don’t think fuel will gum up significantly in the period from last cut to first of the new year.

thanks chaps, pretty much as suspected then.  i wont be free to help him til sunday so that gives him a bit of time to buy a few bits……

You could try that as it likely requires a service, but I would be looking at cleaning the carb and fitting a new gasket there and look at the fuel line. Is the fuel left in the tank relatively clear? Can you see the bottom of the tank?

havent looked at it yet so cant vouch for how clear the fuel is.  can only find crankcase gaskets online at present, will it be called a carburretor gasket?  (EDIT:  found them, £12 from amazon)  will the carb have to come off and be stripped or will a spray of cleaner most likely do the job?

Less safe…Spark plug out, connected to the HT lead and and resting on the cylinder head.
Is there a spark when you try to start it?

A couple of drops of fuel through the spark plug hole, replace the spark plug. It should (at least attempt to) start

why is it less safe?  dangerously so?  risk of electrocution or something?  by a couple of drops do you actually mean a couple of drops? 🙂

take the air cleaner off, spray some carb cleaner over the carb and into the intake – reassemble and hopefully ok.  Oh and check they haven’t turned the fuel feed off!

is there a sponge filter in the air cleaner?  will that need replacing?  and yep, im not expecting him to have made a booboo like that! 😀

thanks for your help, ill keep you posted……….

EDIT due to posting at same time:

I’d take the plug out, give it a clean, spray some quick start into the cylinder replace plug and lead and go from there.

whats quick start?  is it the same as carb cleaner?

It’s not unusual to find water in the float chamber of the carb. If it’s a steel carb float bowl the water will create rust which will choke the carb jet.

Empty the fuel tank, disconnect the tank to carb lines and drain them. If the float bowl has a drain plug, remove it and capture its contents. If there is water in the fuel it will form beads. If needs be, remove the float bowl and clean it. If it’s rusty remove the carb jets and blow through with compressed air.

Remove the plug and give it a dozen pulls to clear out the cylinder. A tiny shot of easy start or fuel in the spark plug hole will help get the combustion going if you have a spark. Clean the plug while its out and check for a spark.

It’s worth taking lots of photos of carb linkages and governer springs before you start dismantling things.

Store fresh fuel in a plastic container. Don’t store it for moths at a time, it goes off.

We had bother storing fuel in steel containers which had pin holes in the top. When left outside in the rain, water would trickle in contaminating the fuel leading to a world of carb heartache

he thinks its because hes left fuel in it since last year and its probably crudded up the engine.

Petrol goes off over time.  First thing I’d do there is (carefully!) drain the tank and fill it with fresh fuel.

“why is it less safe? dangerously so? risk of electrocution or something? by a couple of drops do you actually mean a couple of drops? 🙂”

You’ll produce a high voltage spark, but there’s little current there. You’ll need the metal body of the plug resting on clean metal on the cylinder head

You want enough petrol to produce a combustible vapour mix with air (1:15-ish), so don’t flood it. If it continues to run then job’s a good-un, if it fires then stops it’s a fuel problem

You’ll produce a high voltage spark, but there’s little current there

i know nowt about leccy, but i do remember people saying “its not the volts thatll kill you its the amps!”  so i still dont know why thats dangerous 😀

thanks again for the advice, we’ll have a look at the weekend and follow those steps to investigate.

Mine unusually wouldnt start this year, I did the following which it was that fixed it I’m not sure.

Upend the machine and poor out the old fuel.

Replace with fresh

Clean spark plug

Clean the flywheel thing under the starter pull.

Then its two pulls,leave for 20 seconds pull again and starts ready for another year of grass slavery.

I’ve found that mine will only start each spring with the filter off. That’s with a clean filter, your mate’s may never have been cleaned but it’s easy to do or replace. Avoid letting crud go in the carb obviously.

My mower was a freebie. The filter when I got it was in a right state.

I don’t do the empty out the fuel thing any more, just run it low during the last cut in autumn.

so i still dont know why thats dangerous

I think it’s because you’re producing an unshielded spark in the possible presence of petrol vapour, not any direct harm from the electricity

had this with my lawnmower after a winter…cleaned the carb and it started first time  unlikely that anything has gone wrong with the ignition if it was fine before winter.

Brake cleaner sprayed into the carb (filter off) can also help as a quick fix, or if you don’t have a can of quick start to hand…

If you’ve got a dicky ticker or have a pacemaker fitted then an HT shock from a mower etc could be nasty.  It’ll be around 20kv but very low current (its proved to be surprisingly difficult to google the typical current in a magneto ignition system!).

On my petrol mower and on my bike if i’m putting it away for a long while i turn the fuel off and run the engine till it stops or on the mower just let it run the tank dry.

On the air filter ours benefits from having a dab of engine oil squished into it (it’s in the instructions).

Stripping and cleaning a carb isn’t hard with a bit of you tube watching and a few tools, patience and a logical approach (i.e. laying parts out in order and the odd disassembly photo along the way). You will need new gaskets though.

In line fuel filter may also be worth replacing.

As has been said, it’s likely to just be old fuel, so tip out as much as you can, then fill to the brim with fresh petrol, and try starting it.

If that doesn’t work, take the plug out, make sure it’s clean, and not wet. If it’s wet, I’ll usually run a lighter over it to burn the old fuel off. Then poor a bit fuel in the hole, plug straight back in (finger tight will do), HT lead on, and see if it’ll fire up. If it starts, let it run for a minute or so to make sure any old fuel is flushed out, stop it, and tighten the plug.

If it only starts for a few seconds then dies, repeat the above. If it’s still only running for a few seconds with no improvement, it’ll likely need the carb given a clean, and make sure there’s no blocked jets/split diaphragms.

If it doesn’t even fire, then you’ve got other problems. Could be no spark, or if the mower has been sat somewhere damp, valves can stick causing no compression.

I was going to say take the carb off to clean, it isn’t hard and I think most likely sludge or moisture in the carb. If its been sat around in the damp with old fuel in etc I would go for the full service and as cougar said fresh petrol.

Just another thought, has the correct oil been put in? I used 5w 20 in mine once and within 5 minutes the engine was cutting out and then refused to start. I swapped out the oil for 5w 30 (correct spec is SAE 30) and it worked fine. I repeated this as a test last summer and the same thing happened. I have a hypothesis which is pure conjecture, so if anybody has any ideas please let me know.