Problems this time with an Atco Admiral 16SE, powered by a Briggs and Stratton Quantum XTL 50 Engine. I'm struggling to find any documentation / manuals for both the engine and the document online, even YouTube doesn't yield much.

Upon starting the mower, the throttle / speed is adjustable for the first 5 or so seconds, but then the engine runs at a speed which is no longer controllable by the throttle handle. At this point the throttle lever does nothing and the speed of the engine is the same whether the throttle handle is set at the tortoise or the rabbit. I've tried bending the metal tab that the spring sits into (as is shown on YouTube) but this doesn't sort the problem, either the "fixed" engine speed after running for a few seconds is slow(er) or fast(er) and it still cannot be controlled by the throttle control on the handlebars.

I can (and you can see by the video) that the throttle control moves the little metal tang back and forth which the spring sits into, and then this spring goes through the hole in the governor arm. There seems to be very little tension on the spring when the metal tang is bent to set the engine at a sensible speed (when the "fixed" speed is reached after a few seconds of running) so I don't know how it ever would've controlled the speed in the first place.

The photos and the video show the setup exactly as the mower arrived (apart from me bending the metal tang to try and get it to run correctly!) so I'm wondering if some parts are missing? The spring doesn't seem to "grip" onto the edge of the hole in the tang so it just slides about when the throttle is moved, perhaps this is why no adjustments to the speed can be made? I don't know how this could be modified if this is the case.

I should say the carburettor has been  fully cleaned and serviced and the engine is not surging / revving up and down, I just can't sort the speed of the thing!

Hopefully somebody has some good knowledge of this engine and can provide some insight as to how to sort it out - because for once, the internet can't!

Throttle linkage video here: https://youtu.be/da2zuhNAxxs

Hi everyone,

Picked up a Qualcast Suffolk Punch 30 a couple of weeks ago off Facebook Marketplace. Can't find any builders plates or info anywhere on the mower, apart from the grass box having a green sticker that says "Qualcast Suffolk Punch 30" on it. I assume this is the grass box it had from new but I've attached photos in case this isn't correct and it needs identifying. However, the petrol tank is on the handlebars, with the Zenith carburettor.

When I went to pick the mower up the owner showed me it starting up etc, and it ran really nicely. However, it was running as fast as you'd ever want to run it with the throttle lever on the handlebars barely cracked open, and there was no way to get it to idle.

So, having stripped, cleaned, and adjusted the carburettor to the manual's instructions (3/4 turn out from fully seated for main running speed screw and 1 turn out from fully seated for the idle speed screw) it will now idle, however, full speed now sounds inconsistent and not smooth at all. It's not revving up and down / surging, but the tone of the engine and the exhaust just sounds, well, awful to me.

The exhaust sounds quite loud and makes 'putt' noises sometimes, feeling the exhaust, the blast of the exhaust gasses against my hand is consistent, but the engine doesn't sound smooth at full speed. It just doesn't sound happy, consistent or how an engine should sound to me. It sounds rough.

I know these engines run beautifully when all tuned up as per dozens of YouTube videos but mine won't seem to be consistent at full speed (a sensible 'full speed', not revving the engine as far as it will go, may I add).


Some things I would like some answers to are (in addition of course to any suggestions and advice you have to get the mower running better):

1) How should the throttle tensioner be set?

2) There is a small arm with a screw and spring that touches the carburettor and then swings away when the throttle is opened. This hasn't been mentioned in any manuals I've read or any videos online. How should this be adjusted?

3) The spark plug on the mower turns very black and carbon-y after a short period of running (was clean before today and a half-hour of running has it looking like a piece of coal!) I understand this is due to the mower running rich, but how do I adjust this (without the mower revving too high?)


I'm ordering new gaskets for the cylinder head, carburettor and exhaust and I'll be changing the oil and spark plug as well. I doubt this will help much as they're not damaged, just very old, and like the rear roller drive belt, look to have been on there for donkeys years!


There's my plea for help, and thanks in advance for all your help. Let's get this beautiful old machine working right again!