Ride on lawnmower won't start with electric start but does by manual pull start

[woodman-46]

Hi.
I have a ride on mower with a Briggs and Stratton engine. With a fully charged battery and plenty of fuel when I try and start using the starter motor it turns over strongly but won't kick into life. After doing this I can then do one or two pulls manually and it starts.
Has anyone got an idea why this is? As said the engine turns over really well with starter motors but doesn't start.
Thanks

 

[Burnerman]

How curious!
However, can you make sure the sparking plug is still sparking when you try the electric start? Best to look for a spark in the dark, or at least in the shade.
This is to ascertain the ignition switch is behaving, and not shorting the ignition coil out.
Best tell me which machine this is, and which Briggs engine, if you don’t mind.....the vast majority are magneto ignition rather than battery and coil.
John

 

[Mottie]

We used to have similar problems on the old Vauxhalls back in the day. To aid starting, a 9v coil was used with two feeds - 12v and 9v. When cranking you'd get approx 9v at the coil through the 12v feed from the solenoid as the starter was taking some of the power. When it started, if you continued pushing 12v through a 9v coil, it'd burn out the coil so the permanent ignition feed to the coil would go through a ballast resistor. I think some Fords used the same system. If you had a fault with the starter feed, the car would only start on a push, a tow or a starting handle! Perhaps the lawnmower has a similar system? Try a separate 12v feed from the battery to the coil and then try the starter. If it starts, that's your problem.

 

[Burnerman]

Yep, the revered ballast resistor system......the car would push start but not fire on the starter - no battery juice left!
I haven't come across this system with Briggs gear - which isn't to say it doesn't exist!
John

 

[Harry Bloomfield]

How curious!
However, can you make sure the sparking plug is still sparking when you try the electric start? Best to look for a spark in the dark, or at least in the shade.
This is to ascertain the ignition switch is behaving, and not shorting the ignition coil out.
Best tell me which machine this is, and which Briggs engine, if you don’t mind.....the vast majority are magneto ignition rather than battery and coil.

I would make a guess at the ignition switch misbehaving, wrongly switching the ignition off when it tries to crank. They are also fitted with a range of engine stop interlocks, such as one for making sure the handbrake is applied and someone sitting in the seat, maybe one of those is preventing it starting, I have never come across one with a starter motor and a means to manually pull start it.

 

[jj4091]

I would make a guess at the ignition switch misbehaving, wrongly switching the ignition off when it tries to crank. They are also fitted with a range of engine stop interlocks, such as one for making sure the handbrake is applied and someone sitting in the seat, maybe one of those is preventing it starting, I have never come across one with a starter motor and a means to manually pull start it.

Harry, on ours the interlocks immobilise the starter motor/solenoid as well as the ignition I think they are all the same, B. & S. ones anyway. I'm pretty sure the ignition switch is the same.

 

[Harry Bloomfield]

Harry, on ours the interlocks immobilise the starter motor/solenoid as well as the ignition I think they are all the same, B. & S. ones anyway. I'm pretty sure the ignition switch is the same.

Thinking about it a bit more, you are correct, mine is the same - so I'm thinking it must be the ignition switch shorting the just the ignition. Ignition switch grounds the ignition to kill the engine.

The only other thing I can think of, is I wonder if it is fitted with an automatic 12v powered solenoid fuel shut off, like mine? If that is not opening when cranking, it wouldn't start.

I've attached the circuit for a typical B&S powered ride on..

 

[lostinthelight]

Make sure mower is out of drive and blades disengaged, pull the switch wire off the solenoid , then with the ignition on touch a jumper wire between the solenoid switch terminal and battery live. If it starts , a faulty ignition switch is a good bet .

 

[Avocet]

I'm wondering whether you have a weak ignition coil (or the magnets in the flywheel are losing their magnetism)? The starter motor will rob a good deal of the battery's energy, and your spark might be a bit borderline. By pull starting it, you have just enough current flowing through the coil to get enough of a spark to fire, but when cranking the starter, there's just not quite enough? Does it make any difference whether the engine is hot or cold?

Ours has a B&S engine too, and there's a very small air gap between the coil and the flywheel, which is adjustable (the holes for the flywheel are slotted). I guess you could pull the air cowling off and just see if the coil has slid away from the flywheel on its slots?

 

[lostinthelight]

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