Surging Lawnmower

That looks to be the sort of device that sits in the fuel pipe itself - in Stiga fashion. Pull it out and see what's in there.
John :)
 
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Looks totally clean to me but there was a tiny bit of grass on its outs when I pulled it out. Wondering if there's more at the bottom of the tank
 

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Yep, new carb, new air filter, clear fuel filter, looked in the tank with a torch and that's totally clear. Fuel hose clear.

I guess it can only be the governor spring and arm. Can't be anything in the engine can it?

I couldn't even find someone to service a Hyundai, not sure if anyone would look at it to repair.

Thanks
 
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For sure this is turning out to be a real head scratcher!
The governor is basically a plastic gear wheel driven by the camshaft, and if it spins too quick some bob weights fly out and directly shut the throttle via the linkage.
I’ve never known one to fail, but do check the pinch bolt that connects the linkage rod to the rod that comes out of the crankcase...if the bolt isn’t tight then it is possible for the linkage to move.
John
 
Could it be linked to the pull cord rapidly deteriorating and breaking today? Or is that just the lawn mowing gods not wanting me to cut my grass?
 
I will when I get a new cord.

I started to cut the grass yesterday and each time I had to restart the machine, I had to prime it. I need to have another look for the fuel tank vent, I couldn't see it in the cap yesterday. The carburettor is pretty much right up against the manifold (?) on this machine, there's only a gasket, heat shield (I think) and a solid plastic spacer in between. So don't think there's a air leak there
 
When you press the primer button, a jet of air pressurises the float chamber for a second. This causes a burp of fuel to shoot up the main jet and into the carb venturi which can promote a cold start.
It shouldn't be necessary to use this when the engine is hot so I still think there is a fuel supply issue - either from the tank, through any filters there may be or perhaps in the float needle valve itself.
An air leak can also cause these symptoms but this seems unlikely.......the trouble spot here is where the back of the plastic air filter housing mates with the carburettor itself......distortion here can be a pain.

When replacing the cord, don't remove the central screw of the recoil mechanism - the spring will shoot out like a rocket!
My technique is to turn the recoil mechanism against the spring tension, then lock it somehow as you reconnect a new length of cord. Unlocking the recoil mechanism then pulls the new cord into place.

Hope it goes well!
John :)
 

Hopefully that link to the video works.

It's a new carb so can the needle float still be the issue? I can't see a vent in the fuel cap but the hole in the rubber that's inside the cap is fine. I don't see where it gets to the outside

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The manual has this advice but they seem clear.

Cord change was a doddle, my approach is always to dissemble the minimum amount. I could squeeze the new cord in.

Thanks
 
Where are the governor weights? The link , spring and the bit at the bottom are moving freely back and forth. Could the spring have lost tension?
 

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may not be helpful
but have you replaced all the fuel from last year
are you using E5 / 95% 97% or E10 ???
unlikely but thought i would perhaps mention .....
 
Where are the governor weights? The link , spring and the bit at the bottom are moving freely back and forth. Could the spring have lost tension?

'The bit at the bottom', probably. The weights are flung out, under centrifugal force, which then closes throttle. The surging, and the video suggests that there is an issue of sticking governor.
 
Where are the governor weights? The link , spring and the bit at the bottom are moving freely back and forth. Could the spring have lost tension?
Is that nut at the bottom left of your photo done up tightly to prevent the mechanism from moving on the shaft?
 

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