14" Suffolk Super Punch 75G14-25A
I purchased my mower new in 1975 and it was used regularly for over 20 years. It then languished at the back of the garage for a number of years until a renovation of my garden required better defined stripes on the lawn. Other than replacement of one cylinder bearing, it has served me well until a few months ago when the engine stopped while I was mowing the grass. Not seized, just stopped. I assumed a blockage in the carburetor so cleaned that out, to no avail. On having it checked, I was advised that the spark was weak and intermittent so I have replaced the coil/condenser assembly in the magneto. I now have a decent reliable spark but the engine still does not fire. On removing the plug I can see traces of and smell fuel. Can anyone advise what I should do next ?
If your good spark is off the end of the bare lead I'd perhaps try a new plug connector - especially if yours is the original Suffolk type. A new plug won't break the bank either! What is the compression like?
I can see that the piston moves up and down, and by removing the valve chest cover and associated gasket and baffle, I've checked that the valves are working. I don't know how good seals they make but I can feel compression via the starter cord
I've replaced the suppressor connector and the plug itself - they were already on my list of suspects
My 'good' spark is between plug electrodes, with plug clamped to cylinder head bolt.
I can find TDC easily but am nor sure exactly when the contacts should open. I'd like to check/confirm position of magneto stator plate as it was disturbed when replacing coil/condenser assembly. Perhaps trial and error will work, moving it through its available range
I don't have a compression tester, but if I can get hold of one, what sort of value should I expect to see ?
I don't think that anyone has published compression figures and I wouldn't bother with a gauge; just feeling for a lump when you pull it over is probably sufficient. If you have the cowling off just try flicking the flywheel against compression and see if it has a bit of bounce - Warning - If your engine has a metal governor air vane don't cut your thumb on it. Safer if you remove it.
The screws holding the ignition stator plate usually leave witness marks to realign on. With the points gap set at the recommended 18 thou, about midway in the slots should be near enough but the book figure is 22/24 degrees btdc. You can download a timing disc from the internet or buy a proprietary one. It's possibly easier to take the head off and then using the timing disc to find the correct position, measure the distance of the piston down the bore for future reference and then remove the disc to give access to the stator.
Thank you so much for your help - the beast is running again !
I called in to a local motor parts/accessories place yesterday and asked for a timing disk. The look I got was a complete blank. So when i got the flywheel off (again) I measured the diameter, calculated the circumference and deduced 23 degrees round. The magneto plate was out by about half the slot length.
Putting everything back together, it took two or three pulls to get it started but the engine now runs very sweetly. I would have used it for the purpose intended, but it started raining earlier so I packed everything away and made myself a celebratory cup of tea !!!
That’s good, the first time that I did it many, many years ago when there was no one to ask , I wrapped a strip of paper round the flywheel and did the same. Ingenuity will win out. Interestingly, Suffolk is one of the very few and perhaps the only mower engine manufacturer that gave the figure in degrees, whereas Villiers used to give it in thirty seconds or sixty fourths of an inch which doesn’t mean a lot to many people these days. Just to make matters worse the linear figure cannot be converted to degrees , or visa versa, without knowing the throw of the crank, length of the con rod and a bit of trigonometry .
If anyone wants a timing disc, just google “ download a timing disc” . There are several to choose from , one rather neatly sized to be stuck onto an old CD rom.