I was cutting the grass on Saturday when suddenly the mower lost all power. I did a bit of searching online and there was suggestions of clogged air filters, contaminants in the fuel etc. So I tried a few things then noticed that a spring had bent and come off (below the air filter and seemingly part of the choke mechanism) – I assume I hit something as I pushed it against a hedge . Anyway, I botch fixed it (cut it down slightly and refitted).

All good (or so I thought) now the mower seems to be running more quickly and rather than getting bogged down when hitting deep grass, it seems to be going faster (is this ‘hunting’ in proper terms)? The thing is, the spring isn’t under load when it is at running speed (ie, no choke) so I don’t understand what has happened – there doesn’t appear to be any other damage anywhere that could cause an ongoing problem.

That spring will be part of the engine speed governor mechanism is it not? so its running too fast at tickover but can’t get full throttle as by shortening the spring you have reduced the range of the governor?

I think TJ’s right here, I clonked mine against the woodshed last week and I got the racing.
In my case I bent the thing the spring was connected to, bent it back to looking straight and its fine.

Yeah you’re right – it is part of the governor mechanism. The thing is, there are only two speeds – the tick-over (cold start) and then I pull a lever to set it to the high speed (ie, normal running speed). But now it seems to be running more quickly.

I assume it must be something to do with the spring but (as I said in my OP) it isn’t under load when at normal running speed so why is it now running more quickly?

And I can’t find that particular spring on the B&S parts website 🙁

I guess I am going to have to take a closer look at it and have more of a fiddle then.

Cheers.

Just stretch the spring a little.
When you shortened it you put extra load on the speed governor mechanism.

You’re going to have to replace the thrunge gasket on the triple overhead manifold sprocket.

Make sure you get an imperial one. It should look like this…

All good (or so I thought) now the mower seems to be running more quickly and rather than getting bogged down when hitting deep grass, it seems to be going faster

This is normal – essentially – there’s no ‘throttle’ that you control, but the lever and spring you talk of ARE the (kind of) throttle..
There’s also (hidden away inside) another lever with a ‘flat blade’ that is under spring tension – in it’s ‘under tension’ position the carb is open. When the mower is running, the fan that is connected to the blades ‘pushes’ the ‘flat blade’ lever towards teh closed position, thus regulating the carb opening..
When you go into long grass, the blades slow down, the fan slows down, the ‘blade lever’ returns and the carb opens up more, thus speeding up the blades! Simple but clever.

The spring you (and I) broke on our mowers, as suggested, adjusts the tension of the ‘flat blade’ and can force the carb open – mower can tick over too fast..

THe trouble is, the spring tension is actually quite specific, so my bodge, though working, isn’t as perfect as it would be with a new spring..

DrP

All makes sense – for the sake af a couple of quid (if I can find the correct part) it sounds like it will be most straight forward to just replace the spring.

Thanks all.

You’ve tuned it up.
Move on
Tim

I like your thinking 😀

Can anyone help with Googlefu – I can’t seem to find the correct replacement part – it’s for a MacAllister mower with a Briggs & Stratton engine (Model 90000 Sprint 475 with a 158cc MPRM 46HP engine part number 295495024/MCA)

Does anyone know of any online parts supplier that might stock it?

Cheers

you’ll find the supplier..the spring will be £9.99, and you’ll leave it….

probably!

DrP

GHS have most parts, tend to be cheaper postage through eBay too. Search for the engine, not the mower.

Cheers – I have now found a stamp on the engine which is yet another serial number….

I have a long term problem with mowers. I have tried all types and I am now using a top of the range Bosch one. You see they all only work in the winter. In summer I cut the grass and it looks lovely but a few days latter it looks the same as before. Thankfully it will settle down in a few weeks but will do this strange thing again next spring. My neighbour hardly uses his mower on his gravel .Please help me if you have overcome this syndrome.

you’ll find the supplier..the spring will be £9.99, and you’ll leave it….

£12.07 including ‘Signed for’ postage (the only available option FFS)!

😯