Briggs & Stratton Engine won't start on petrol mower

[JT101]

Hi

I have a Makita PLM 4601 petrol mower with 4HP Briggs and Stratton engine

Bought it secondhand but it was in very good condition and the guy said it had just been serviced

Oil looked, and still looks clean and is full.

It was working fine the first couple of goes infact, but now just won't start. Definitely sounds strange, and gets very close to starting. Plenty of unleaded petrol in the tank.

I prime it 3 times, sometimes more, but makes no difference.

Here is a video:

I am definitely a newby to these sorts of engines but willing to learn.

Thanks

 

[HERTS P&D]

John will be along soon.

Andy

 

[lostinthelight]

From 2 mins into this vid.......

 

[Burnerman]

A genuine Briggs gasket is a very good move on these.....the fuel has to be pumped up from the tank before it can enter the carburettor.
If you take the carb off the tank, look for a nylon gauze filter on a pipe that descends into the tank, and you'll need a diaphragm and gasket as a pair. Keep them the same way round!
John

 

[stuartb3502]

Check spark - wear rubber gloves/wellies to be extra safe or just make sure you're holding the rubber boot/not metal of the plug. Hold against bare metal of engine while some gives the starter a pull (or buy a spark tester to make this even easier/safer).

It's usually fuel supply rather than the spark on these, but it was the problem on mine recently so should be eliminated since it's simple.

After that, the suggestions above should help - clean/replace intake gauze and make sure hole in intake tube is clear. You have to remove carb to do that, so you can check the gasket. My understanding is that it would have to be very bad to prevent starting (normally a wrinkled gasket causes surging).

You can also check that the governor valve is moving freely before having to remove the carb. (the V shaped piece with two springs attached. Should be moving freely. Unlikely this would prevent starting however.

Failing that, replacement carbs (and even tank + carb. assemblies) are not that expensive if you want to go for the simpler/more expensive option since you don't know really know the history.

 

[JT101]

Thanks guys. Should have posted this video of what it was doing before it stopped working. Not sure if this gives any more clues.

 

[Diver Fred]

Decompressor not reseating.
Or Piston Rings seized in Piston.

 

[Burnerman]

It’s a bit smoky, that one.....however, lets not panic yet!
A couple of questions........did you tip the mower onto its side before the video? Is the oil level too high?
John

 

[JT101]

Sorry I took so long to reply. I was trying out a few things. In answer to your question I don't remember if I tipped it into its side so I could clean the grass out. What would that do?
Oil level looks ok on the dipstick

So I bought a service kit. Replaced the diaphragm and gasket (which looked fine anyway), push button, sponge filter and sparkplug. I cleaned everything thoroughly with carb cleaner and made sure it was dry. It's still acting the same (see video):

Any thoughts?

When I bought it from this guy, he said it had just been serviced. From the get go it was smoking out the side like in that first video I posted. I wonder if that is a clue

 

[Burnerman]

This engine has a peculiar sound when you crank it over......just like the cylinder head gasket had blown, with that chuffing noise.
Pull the plug out, isolate the cap and get some one to pull it over when you put your thumb over the plug hole. If there is compression it will be impossible for you to keep your thumb there.
John

 

[ASK1950]

Sorry guys I am new here and wanted to know I have a Makita PLM 4601 lawnmower and kind of stuck, No current coming through. Any suggestions please? I have checked kill switch, it's off,

 

[Burnerman]

Remove all of the wires from the kill switch - don't let them touch the engine!
Check for a spark at the plug now, ensuring the plug is sitting on engine metalwork.
No spark now? Change the plug and try again.
Failing that, the igniter could be at fault.
John

 

[JT101]

Hey guys. Made another attempt at this, and am honing in on the problem but still not there. It now only start if I did 10-20 primes of the bulb. Wouldn't restart from warm unless I primed similar amount again. So I cleaned the entire carbuerettor and fuel tank, replaced the gasket & primer bulb with genuine parts, and put in fresh E95 unleaded petrol. Fired it up and no difference. Spark plug was also cleaned, and correct gap set. I noticed the primer bulb is fine when system open, but slow to release when pumping the petrol (well at least I think so), so definitely seems like some sort of blockage but not sure where.

Second start in the video is interesting because I only managed to get it started by tugging repetitively and quickly, so almost catch the momentum of the first tug if that makes sense. Skip to about 2mins in and you'll see

 

[jj4091]

I had a similar problem to this on a petrol mower but it wasn't a B & S engine. I believe however that the governor works in the same manner ie centrifugal weights in the crankcase move the lever either closer to or further away from the carburettor acting like a choke and throttle at the same time. As it was a favour job I did not want to strip the crankcase so instead i fixed a piece of stiff wire to the engine then moved the lever forward and held it in place with the wire . The engine then started without any problem.

 

[Burnerman]

Right now I’m rather intrigued with the sound of this engine......chuffing, in fact.
Look at the join between the cylinder head and cylinder. Is there any sign of oil leak or carbon staining there?
John