[andyfrost]

When you have backed off the piston as you have done, this is then when the points should be cracking open. Personally I never take no notice of the timing marks , as over the years mixed parts may have been fitted.
The fan on the flywheel “should” be a seperate part , and once removed you can adjust points with flywheel in place.
Some close-up pictures of your flywheel would help.

Andy.

[andyfrost]

From your description it sounds as if you’ve got timing issues , try advancing the timing fractionally.
You need the flywheel in place to both set the points correctly , and set timing.
If there’s no improvement after re-setting , get back to us.

Andy.

[andyfrost]

One of the extra long deep nuts that join allthread together will do just fine.

Andy.

[andyfrost]

Shanks must have been a very diverse and very capable buisness. I remember as a youngster going to a local steam engine rally , and the landowner always had his Shanks Hotbulb oil engine on display, it was quite a large engine , so they must have had means of producing very large castings.
After the rallies finished , I never have seen , or heard of where this VERY rare engine went , hopefully it’s in someones collection.

Andy.

[andyfrost]

The fact that you say it starts OK and runs for 30mins , would maybe suggest that you’re looking for a problem that isn’t there, if the main bearings are still tight , the glans seals gave little trouble.

Andy.

[andyfrost]

As Geoff says , take it one step at a time , the plug is the first(and easiest) thing to check.
My next step would be to have the coil PROPERLY tested.
As you say it runs for 30 mins , it doesn’t sound fuel related.
When it runs , does it develop plenty of power ??

Andy.

[andyfrost]

That really is a beautiful item , unsurprisingly I’ve never seen another.

Andy.

[andyfrost]

It’s also worth remembering that by using the module you will have done away with the govenor system. Not that it overly matters as Allen, as far as I know were the only 25C customers that had it fitted , every other customer had a plain system , and by careful hand use of the throttle gave no problems.

Andy.

[andyfrost]

Angus , have you timed it according to the marks , if so it’s worth remembering that these marks were stamped in by shall we say more inexperienced staff or apprentices , and I’ve known them to be “out” enough to give poor running/starting issues , far better to look at when the points are just cracking.
Webb 24s gave the same problem , if not timed exact , again no extra flywheel weight.

Good luck Andy.

[andyfrost]

I know it can be a bit of faffing around , but I would try retarding the igntion VERY slightly.
Very unusual mower , can’t say I’ve ever seen one before.

Andy.

[andyfrost]

Sorry , can’t help on the ID plate , your engine date I would say is correct.

Andy.

[andyfrost]

That is a Mk25 , nice to see it retains the original and correct carb. My Father used one extensively on his smallholding from the late 60s and through the 70s until he retired. From very distant memory he converted the body to dropside , originally I believe it was used as a milk cart.
Mk 25s are still relatively common, so sourcing a cowling should be quite straightforward.

Good luck with your restoration of what is our hobbies more unusual machine.

Andy.

[andyfrost]

Superb , just how I like to see a machine , lovely original look.

Andy.

[andyfrost]

Your de-compressor is indeed original , it should be fitted with a cable to a small thumb lever fitted on the handlebars.
Remove it from the head , drop it in a can of diesel for a fortnight , go back to it and it should free off OK.

Andy.

[andyfrost]

Lovely good old fashioned engineering , but sadly hopelessly underpowered.

Andy.

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