We had and I maintained two industrial Flymos years ago: they can be infuriatingly tempramental. None of this may be useful, but just in case:
- You will almost certainly need a gasket set, and probably a spare Woodruff key for the impellor, if they still use that system (DAMHIKT!).
- The ones we had were around 125cc, crankcase compression, with a reed valve to seal the crankcase. If that valve, or the crankcase itself, isn't sealing properly, you won't get the thing to compress sufficiently. Reed valves for them used to be cheap, so I would change that, if you can.
- The choke on both carbs was rather too enthusiastic. I got better strarting on half or two-thirds choke, although that was often rubbish.
- They needed a much stronger 2-stroke mixture than my bikes did: 15:1, IIRC, possibly as low as 12:1. This is in part because of the crankcase compression - with a dry crank, all the big-end and main bearing lube comes from the 2-stroke mix. It wasn't a good system (we wore out one Tekumseh engine completely - knackered almost everything). I'd expect that too much oil would be smokey, and tend to carbon/oil up the plug, but otherwise won't hurt.
- For the first few runs after the winter, I used to cook the plug, either on the stove or with a blowlamp (clean it first). It helped a bit, I think.
- Because they use a rich mixture, both oil and fuel-air, the silencer does get gummy. They are quite sensitive to back-pressure, so this can be a nuisance. It won't hurt to de-coke it carefully. The traditional technique was caustic soda in a bucket (make sure you get the air bubbles out!), then rinse really thoroughly (hose to flush out residue thoroughly. To prevent/minimise flash rust, you can then cook it up and squirt the outside with WD40, which will (sort of) re-blue it, or pour engine oil over it whilst it's really hot (just the outside).
- I'm not sure EZ-start is a good idea because of the dry sump (sorry to disagree on that, Lons).
- The pair we had used two different designs of air filter: The later one had a block of foam, but the earlier one used a proper filter on the handle, connected to the carb with a hose. Flymo recommended putting 2-stroke oil into the foam, one to make it sticky and collect smaller dust particles, but in my experience that upset the aspiration a bit. I wouldn't bother with the oil. You are supposed to be able to clean the foam with soapy water, but (a) it's very hard to dry off afterwards, and (b) you cannot properly get all the crud out of it: I'd replace the foam too.
- Assuming it's a Tekumseh engine, setting the points gap is nigh-on impossible: the points are under the flywheel, and a lump on the flywheel causes them to open. Tekumseh must have used a jig in the factory. There is probably an elegant way to do it, but I never found it! As they wear (or the cam action wears), the gap widens and the spark retards. I don't remember any auto-advance system. retarding the spark will affect high revs performance, but it's of little relevance to a Flymo. I'd clean the points, with very fine wet+dry pulled through, but try as hard as possible not to disturb the actual setting.
- Check the condenser too, as they really do need a thumping spark at the plug, not across the points, as the ignition system isn't very sophisticated, and the spark on ours was pretty weak. IIRC it's an old-fashioned car-type, so ought to be fairly easy to find.
- These are low-compression, de-tuned engines in the main. They don't like running lean/hot, but they will put up with a lot of abuse.
So there are many things that might upset them, and the poor starting is probably a combination of several. You'll have to go through methodically, checking everything as you go.
It's hard to tell from your picture, but it does look rather cruddy inside. That's a good-ish sign though, in a way, as it implies it has been running with 2-stroke mix for a lot of its life. I think I would take the head off and de-coke gently and carefully, if only to prevent lumps coming loose as you say. If Naz's suggestion of a squirt of oil does bring the compression up again, it's a good sign the bore/rings are shot, and the engine is probably beyond economic repair - I very much doubt you'll get oversize pistons/rings, so a rebore would be off the agenda, even if it cost a sensible amount. And anyway, as I said, the big ends and main bearings are rather vulnerable on these (also when the blades hit stones, etc.) and won't have fared well if it's been run without 2-stroke.
Finally there may be an in-line fuel filter somewhere. One of ours didn't have one and one did. They get gummy and can be flushed with meths. Also, assuming you can get it started, check the carb paddle spring(s) tension - if in doubt set the tickover higher rather than lower (once the engine is warmed-up). It helps with starting (once it fires!), and if there is some blowby (worn rings, etc.), it will be less prone to stalling in use.
Something in that lot might be useful!
E.
PS:i have a vague memory that I used ordinary 80g paper as a makeshift head gasket: I think one of them had no gasket at all, but relied on a smear of Hermatite or simlar at the factory. Check for signs of leaks (staining on the outside around the head-barrel area). As I said, they're de-tuned, so a leak isn't necessarily a disaster - try sealing with a tiny amount of Hermatite (if it doesn't have a gasket), and failing that, paper cut to shape then dampened with engine oil. Don't overdo the head bolt tightening when you reassemble - IIRC there isn't much female thread on them. You might find a torque setting on-line nowadays, but at a guess it'll be lower than ordinary car torque wrenches will go. The "bolts" on ours were actually cross-slotted machine screws (not even Phillips headed).
