Lawnmower Engine Not Firing

pdpdpdpd

Mountfield/Stiga 13hp TRE0701 Lawnmower engine.

Carb all clear, petrol flowing, jets clear, air filter clean and fresh, new spark plug, battery fully charged, fresh carb gaskets fitted.

Starter kicks in fine and turns over fine. Coughs a few times but no spark. Then whirrs and stops.

Is this an electrical issue with the spark plug? How do i check if there's spark at the plug? Are there other checks I can do on the electrical side? Is it compression? How do i check that?

Learning as I go, so apologies if these are stupid questions and youtube is a great help but just kinda stuck now.

feartuath

You say starter stops, starter should still turn over the engine regardless of fuel or spark until you switch off the key.

Can you elaborate.

Can you pull spark plug and check continuous spark until you switch off key

pdpdpdpd

Hi feartuath

Seems to be a some sort of protection. With key held on the starter will run for about 30 seconds and then seems to disconnect. Will turn over again fine turning key off and on again.

Pull spark and check for spark - is that the check I see on youtube of pulling out the spark plug and touching it against the chassis? Gonna try that tomorrow.

Ta much

amandstu

https://www.boards.ie/discussion/comment/123602998#Comment_123602998

Just be careful with that procedure.Whilst you are probably not as daft as me I did manage to set my mower on fire once when doing this as there was (from ancient memory) spilled petrol on the chassis and the spark from the plug must have ignited the fumes.

I never had to work on that machine ever again.(it was pretty hairy at the time)

By the way ,just to reinforce how dangerous these machines are ,this year I manage to damage my finger as I put my hand too close to the spinning blade which gave the faintest touch to the end of the finger but caught the end of the nail and lifted it partially.

Really,really lucky but also really stupid .

The nail healed fine even though there was blood at first .Could have been so much worse.

mickdw

Probably nothing too serious if it was working when parked.

I'd remove the plug, turn it on the starter then. It should turn really fast without the compression. Will clear out any petrol that made its way to cylinder too.

Ensuring that no petrol or petrol fumes around the engine, put plug into plug lead and rest plug thread on engine metal and turn over. In fading light you should easily see a regular spark.

If you have spark and you are fairly confident that carb is doing its job, I'd give it jump leads and get it spinning faster. Should go.

If no spark, it's a pretty basic system. The spark timing is picked up off the spinning engine. There is only the plug lead and a stop cable coming off the coil unit that generates the spark. The stop cable just earth's to stop so with that small cable disconnected, mower will run but not turn off.

You should be getting a strong petrol smell if its getting petrol when turning.

youtheman

I have a ride on lawnmower. I find that if the battery is not absolutely fully charged then the engine doesn't start. The starter motor turns it over, it sounds normal but it just doesn't kick in. So I'd check my battery first.

Wearb

Some mowers have oil level sensors. Check proper oil level.

pdpdpdpd

Hi Amandstu

Setting fire to the bloody thing did cross my mind. Would be great excuse to get a nice new robot one. :-)

However, spark plug is sparking good o.

At a loss now. There was a little oil in the rocker cover - what does that indicate?

BENDYBINN

spray a bit of easy start into carb…….if it fires for a few seconds then u know ur problem

The Ging and I

If the petrol is old, drain it off and get fresh stuff.

The Continental Op

E10 petrol seems to be wrecking aluminium carbs. I'd get the carb off and give it a full clean - check youtube. Even a (chinese) replacement won't be that expensive.

If that proves to be the problem in future drain it down over winter and use an additive in the fuel I'm try B&S Fuel Fit this year.

blackbox

If the spark plug is sooty or wet with petrol when you remove it, try heating the tip with a blowtorch and put it back hot (gloves!). If you haven't got a blowtorch, use a lighter.

If you can get it to start it will probably clear itself out.

Barcley

I know some people criticise this approach but it always works for me when a lawnmower won't start or has been laid up for a long time. Remove the spark plug and put a thimble full of petrol in the cylinder, screw the plug back in and reconnect. The lawnmower should fire up first or second time when started.

The Continental Op

https://www.boards.ie/discussion/comment/123605390#Comment_123605390

I used to cut acres of grass every week around housing estates with a gang of lads. That was a first IA for any mower that wouldn't start. If it fires you know the spark plug is working if it fires then fizzles out then it has to be a carb issue.

amandstu

https://www.boards.ie/discussion/comment/123604034#Comment_123604034

Not familiar with that personally but a quick (AI) search seems to indicate it should not be serious and that maybe the engine gasket is leaking a little oil,.

Now ,with my own mower I had,this year a badly fitting gasket over the carburetor float chamber which seemed to have been making the engine cut out( the situation did improve when I sat it properly in its channel)

I also have a problem where one of the cables (actually the lever it moves) over the carb sticks and I sometimes have to free it very quickly by hand in the seconds after it starts or it stalls.

celtic_oz

I had this issue and had to drain the petrol and add new stuff.

"ethanol, a component in some petrol (gasoline) blends like E10, is hygroscopic. This means it readily absorbs moisture from the air. This can lead to phase separation, where water and ethanol separate from the gasoline, potentially causing engine problems"

Asus1

https://www.boards.ie/discussion/2058418723/lawnmower-engine-not-firing

I'd say it's solenoid starter,cheap and seem to always go.Get yourself a pair of insulated pliers and cross it while turning over ignition.

Mine goes so often I don't bother buying new solenoid unless passing place that sells them