hiya mate, luckily for you, i also restore PETTER A's, A1 especially, theres several things you need to watch out for.
The magneto connection to the crank case, (the aluminum bracket crystalises and breaks apart as soon as you take it off, these are very hard to replace,
The gasket that goes between the cylinder head, and the barrel, is made out of copper, they can be brought for about £6, I cant remeber off the top of my head where, although i know you can buy them fairly easily,
Best bet for now is check SEM (stationary Engine Magizine). There are several stockist though and i will continue to do my research into which it is.
On the compression side, of things simply either one of the following, take the head off, and de coke the engine by removing the vavles, be careful as the colics ping out and are very difficult to find, clean the valves with emrey cloth, then with sand paper or maybe a chisel if its really lumpy scrap off the crud, then using griding paste, corse to start with, grind the valve back in, i dunno if u know how to do this but ill tell you nehow, its as simple as 4 steps:
- covered the seat in the griding paste
2.place valve back in it checkin its the correct one. EX on the left side, ive always found.
3.twist it with a screwdriver and let the valve make the paste go green, simple keep turnging alternate directions and eveyr so often pick up the valve spin it round n drop it back in, and proceeed again untill u get a dull grey line round the top of the valve and the edge of the value hole. roughly about 2 mm thick,
- replace the colic with a valve compression tool.
or the easier way although im not sure if it will work, is to, (ive used this method and it dose work) if u are sure u have fuel into your engine via the carb take a syringe and fill it up with 5 ml petrol spray it down the bore, replace the spark which should be a C14 lodge, i do have conversions if you need it, then crank it over, it will fire very rich but it the engine is correct it will get it going the the pistion will bind itself back in. please remember this is what i use, maybe not the best of solutions but it makes the engine run,
Martyn, hope it helps, ill try and find them numbers for you, and i may as well post the conversions for the spark plugs anyhow for a PETTER A/A1
PS: hope it goes well, there great engines, in my eyes, please just check the cowlin is in wicked condition if not i recommend you dont run it any longer than a few seconds, me