Atco Admiral 16SE, Briggs Quantum XTL 50 Engine - Throttle / Speed Problems

[suffolkpunchman]

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

[Mick]

The linkage looks ok, though this particular version really isn't designed to be used as a throttle as such, and tends to be used on fixed speed machines. Really only needs to vary the speed a couple of hundred RPM between high and low.  They are not designed to idle.

Here's one I serviced a couple of weeks ago,  https://youtube.com/shorts/w80Nrhn0QbM?feature=share

[suffolkpunchman]

I think I'll have another go at setting it tomorrow then now I know that it's not a throttle as such. Doubt it'll make any difference but I'll try move the throttle cable to the other side as well and see if I get any improvements.

You don't by any chance know how to get to the drive belt pulley on the engine do you (do you have any photos of what it should look like?) I've taken off the plastic cover but all that reveals is the rod that alters the height of the wheels. Was thinking of taking the engine off to get a better look?

[Mick]

You don't by any chance know how to get to the drive belt pulley on the engine do you (do you have any photos of what it should look like?) I've taken off the plastic cover but all that reveals is the rod that alters the height of the wheels. Was thinking of taking the engine off to get a better look?

The pulley on the engine is just pinned to the pto shaft with a roll pin.  To be honest I wouldn't bother removing the engine unless you need to get inside it for some reason.

There's a breakdown image here,  https://www.diyspareparts.com/parts/atco/diagrams/f016l80473/1887/

[suffolkpunchman]

There is currently no drive belt so I'm currently trying to access the mechanism / PTO shaft to make sure it is all in order before ordering a new belt and also find out how I would go about installing it.

[Mick]

You should be able to see the front pulley etc from the little cover on the left of the machine, the one held in place via one screw.  Also make sure the little toothed belt at the back is also ok and doing what it should. Does make me wonder though why the main belt is missing.

[Mick]

Take a few photos of the machine and attach them, I'm interested to see what's what. 

[suffolkpunchman]

Work has been sparse and unfortunately probably will continue to be due to incoming bad weather (and bad news!) this week.

There is no pulley on the PTO shaft as I began to suspect. Just this weird shaft thing that's still pinned in place. The height adjustment lever also looks like it's bent / not fitted correctly as currently there's no way a pulley could've ever been on there without scraping on it (well, actually, that's precisely what the paint shows it's been doing. What I mean is that's obviously not the correct setup).

Looking at a YouTube video which I managed to find of the PTO shaft / self drive mechanism I can see what the pulley should look like. Unfortunately the internet does not seem to hold such part. I'm aware it's a redundant mower with very few parts available.

I may (unless you have any better ideas or sources of these pulleys) try to set the image on screen to scale and get the dimensions for the pulley from it, and try to 3D print a prototype part. Then if it fits I'll see what sort of cost it would be to get a metal one machined.

Going to try to keep costs as low as possible, but still make a reliable repair, as this is a "repair for profit" mower!

The back pulley on the roller side is fine, rotating when the roller does and is all free moving, so that's a small bonus, I guess.

[Mick]

Looks like the connecting rod has actually worn right through the sleeve part of the pulley and it's dropped off.  I've not seen one do that before.

They also suffer from broken roller frame mounting posts which are part of the main deck, so be very careful when doing any work there. 

[suffolkpunchman]

The connecting rod as in the height adjustment rod?

Did the pulley originally slide over that piece that's still pinned in place and then get pinned by the hole that's behind it on the actual PTO shaft.

Current awaiting some more Allen keys to get the blade off (damn Atco making it a size I don't have!) and then I can take the engine off to take some measurements for designing.

I've realised that it seems to be a bit of a mower that's not necessarily designed to be taken apart, I've encountered a seemingly random mixture of metric and imperial nuts (in the same location too!) upon disassembly, and an Allen key for the blade too? Anyway, I shan't be beaten!

[Mick]

Did the pulley originally slide over that piece that's still pinned in place and then get pinned by the hole that's behind it on the actual PTO shaft.

The pulley and sleeve are a one piece affair which slides onto the PTO shaft and is then pinned to the PTO shaft on the engine.  I did a mock up for you (not to scale but gives you an idea). 

[suffolkpunchman]

Thanks Mick, that is a really helpful drawing, was useful to have when trying to remove the broken shaft earlier. I didn't realise until you posted this that it was a single piece, as by the photos and description I gave, I thought the shaft still on the PTO had an 'end cap' on it so to speak, I didn't realise it was open ended and it was the PTO shaft I could see sticking through it, hence why I thought it was a 2 piece affair that used both holes in the PTO shaft.

Managed to get what was left of the pulley off of the PTO shaft, took a bit of hammering with a punch but the roll pin and remaining shaft came off. You can see in the first photo just how (paper) thin the end of the shaft had become.

Currently in the process of designing and prototyping a pulley, shall let you know how that goes. If my fix works I shall make sure it is very well documented on the internet!

[suffolkpunchman]

I finally have a fix! Sadly not guaranteed for anyone else to work, but feel as if I should share the outcome.

Ended up ordering a 60mm diameter V-belt pulley with an 18mm bore and fitting it onto a sleeve that was a good fit over the PTO shaft. Tightened the pulley onto the sleeve with the 2 grub screws and was nice and secure. However, pulley massively too big, belt was really tight once fitted and self drive constantly working. Intended to machine it down but getting access to a lathe has proved difficult.

Put up a post on Facebook Marketplace asking if anyone had one for the Briggs Quantum XTL 50 engine, one bloke did, offered to send me it for nothing! I gladly accepted and it is on its way as we speak.

I will however post a full set of dimensions on here once it arrives for anyone in future wanting to machine one themselves or make / send off their own CAD model to be machined. I imagine it's a pretty unique problem but I might as well provide the information I wasn't able to from the internet.

I believe I also discovered the reason why the pulley had worn through and dropped off in the first place. There was a missing rubber engine mount that fits between the plastic deck mount and the engine on the pulley side of the mower, causing the mower to be tilted down to the right (when viewed from the front). As a result the pulley was contacting the height adjustment rod. After a replacement rubber mount was made the engine sits level, and there is plenty of room for a pulley to fit in there without interference now. Still baffles me as to how it had worn through though.

Will be back to let you know the overall success of the mower once pulley is fitted and final checks done. Throttle seemed to be better last time I started it up after some fiddling and bending the metal tab upwards a bit.

[suffolkpunchman]

Hello all, it's been a while. I have good news on the mower! As spring is beginning to arrive I have once again been able to get outside and do work on the machine.

Pulley from FB Marketplace was fitted just before winter last year, and I'm glad to say it has done the job really well. Self drive now working brilliantly.

Throttle problem is also now remedied (although carburettor needs another quick clean as still hunting a little bit, but I do have now some proper carb spray and cleaning gear). The throttle problem progressed further before it got better, upon starting the mower it would rev out of control and sounded as if it was about to go into orbit! After much faff I ended up tinkering and resetting the governor, as it seems either it had slipped out of alignment or the previous owner had mucked about with it. Throttle is now lovely and controllable and the engine runs at a good steady speed.

Microswitch for the electric start was replaced as had started to fail, and I also ended up replacing the battery connector too on the mower's wiring harness as it was perishing away and didn't fit all too well into the battery itself.

Hopefully I can finally sell the thing now and move onto something a little easier (Briggs 35 Classic, anyone?)

Thank you again for all of your help!