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Collection, Preservation and Display of Old Lawn Mowers

Atco Commodore 17" keeps stopping

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I could really do with some technical advice/help on a problem I have with my Atco, I have had the mower for about 12 years now (was 2nd hand when I got it) so its about 30 years old maybe a bit more, has always been pretty reliable and cuts the lawn well. Unfortunately my father who could fix anything and who was the one who rebuilt this sadly passed away in a tragic accident 18 months ago - I'm pretty handy with mechanical things but this has got me stumped.

So the symptoms - (was fine all last season), have used it about 3 times this year and after starting fine, it runs normal for about 10-15 minutes then just cuts out with no warning, this is a bit of a cough as it stops but nothing more, no rough idle or issues running - just stops - and will not start, leave it for about 4 hours and it will start again no problem and do exactly the same.

I have changed the oil, which I do at the start of each season, and have ordered a new spark plug, which was a bit sooted up, have taken the bowl off the carb and just checked petrol flow and jets, which all look fine as far as I can see, have put Redex in the fuel just to help out a bit, and have also ordered a new head gasket.

I have taken the cowl of and cleaned all dust and grass from behind that and thats all good now, wasn't too bad anyway, 

So am not sure if its something more electrical related or if its the head gasket again which I have had to replace before about 4 years ago, it does seem like an overeating issue or a semi sieze  ?? if thats possible, 

I'm really stumped as what this could be now - so any advice from anyone on here is very much appreciated, I could just get rid of it but it has sentimental value to me and I know my Dad would have fixed it !!

Forums

wristpin Mon, 20/05/2019

Likely options. First a blocked or partially blocked vent hole in the tank cap. Next a blocked filter on the fuel tap. Arm your self with a glass jar and pull the fuel pipe off at the carb end, open the tap and watch the flow into the jar . If it maintains full flow for 30 seconds I think that you can discount the above.

Next possibility is that the electronic ignition module is overheating and failing . So as soon as it stops move it into the shade. make sure that the ignition / throttle lever is in the Go position , remove the plug, remove the plug cap from the end of the lead and hold the lead 3/16 - 1/4" away from bare metal and pull the rope and check for a spark. If there is a spark it might just be worth trying a new plug cap and plug but they are not usually heat/time sensitive. The electronic modules are sensitive to overheating and its important to keep the cooling fins etc clear of debris . If it comes to pulling the flywheel and removing the module the usual sign of trouble is that the hard plastic shell is separating from the "potting" material abound the rear. 

After that it could be tight valve clearances but start off with the simple things!

IanJ Mon, 20/05/2019

Great stuff ! thank you for the quick reply and pointers, I think I am good with the fuel side of things, as most of this was replaced last autumn, with new parts, but I will check first for sure.

I didnt know about the ignition module, but this makes sense I think, and could be the most likely - I assume these are available as spares? from somewhere?