# Lawnmower engine



## Mark A (28 Jun 2017)

Hi chaps,

My parents' old 2-stroke Flymo hover mower won't start. It's a L400 Domestic.

I drained the fuel tank, and what did I find? Neat petrol, not even a hint of red, meaning they ran it with no oil in the fuel...

Despite that the engine seemed to turn over easily, so I cleaned the carburettor, changed the spark plug and tried to start it but still no joy.

Any suggestions?

Cheers,
Mark




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## katellwood (28 Jun 2017)

Have you tried selling it to Rodney Trotter :lol:


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## Mark A (28 Jun 2017)

Another question:

When I pulled the starter cord while holding a finger over the spark plug hole I didn't feel hardly any pressure. I assume this means it has very little compression?

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## NazNomad (28 Jun 2017)

Do you have a spark?


pmsl, katellwood... ''Listen, they're not ordinary lawnmower engines......"


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## katellwood (28 Jun 2017)

NazNomad":ojf170ta said:


> Do you have a spark?
> 
> 
> pmsl, katellwood... ''these aren't just any lawnmower engines....."



"No they're broken lawnmower engines


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## Mark A (28 Jun 2017)

NazNomad - yep, there's a spark.


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## NazNomad (28 Jun 2017)

Get the exhaust off, see if you can see the piston rings through the exhaust hole.


If the compression is that low, might be worn rings. Try a dash of oil down the sparkplug hole to get the compression up a bit, then try it.


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## katellwood (28 Jun 2017)

seriously 

As you have a spark and its not firing is the plug getting wet with fuel, if not give the carb a blast of compressed air.

as its been run without 2 stroke oil the rings could have worn ergo no compression.


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## Mark A (28 Jun 2017)

Hi chaps,

I've just dismantled the carburettor and cleaned it thoroughly. The diaphragm is good. 

Now onto stage 2. 
I've removed the exhaust and I can see scratches on the side of the piston. It also looks like there's a lot of carbon build up on the front of the piston. I know if flakes break off they can scour the sides of the cylinder.

Do you think that's enough to warrant removing the cylinder head and cleaning all the carbon off? 

Cheers,
Mark

Looking through exhaust port






Looking through spark plug


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## Lons (29 Jun 2017)

I'd buy a can of engine start and spray through the inlet of the carb with the air filter off, it's not expensive and worked several times for me when like an silly person I hadn't drained the tank over winter and gummed up the jets.

Just a check on the engine: Many like mine are 4 stroke not 2 stroke and therefore do run on neat petrol are you sure which type is yours? Have you cleaned the air filter btw and checked if fuel is actually getting to the carb?

Bob


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## Eric The Viking (29 Jun 2017)

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).


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## Phil Pascoe (29 Jun 2017)

And the lesson here is - buy mowers with Honda engines.


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## Beau (29 Jun 2017)

phil.p":26kiphsj said:


> And the lesson here is - buy mowers with Honda engines.



That's what Flymo use now. Don't think any two stroke will last long without oil.

Sorry OP not much help I know.


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## NazNomad (29 Jun 2017)

phil.p":gn0iv839 said:


> And the lesson here is - buy mowers with Honda engines.



Hell yes.


The good thing about this engine though... it's not a Villiers. :-D


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## Mark A (29 Jun 2017)

Eric - I appreciate the time it must have taken to type all that, so thank you! 

This Flymo only cost £50 last June so I think it's still worth tinkering with, providing it doesn't need any major work like reboring. 

I'll continue playing with the Flymo tonight.

Cheers,
Mark

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## graduate_owner (30 Jun 2017)

Interesting stuff. I have a Flymo contractor 52, hover plus 2 wheels. Brilliant piece of kit but it went bang one day and 
I have little idea when it comes to 2 stroke engines so this post could provide the solution for me, or at least I will have an idea of whether to try a repair.

K


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## Eric The Viking (30 Jun 2017)

Very similar to the ones we had (both were Contractor 47Ts, which I think were earlier versions).


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## Jonzjob (2 Jul 2017)

phil.p":167qtrbv said:


> And the lesson here is - buy mowers with Honda engines.



What the same as Maclaren F1 team do!

I had a flymo like that and never got the dammed thing running. I finished up giving it away. So good luck.


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## bugbear (2 Jul 2017)

phil.p":1mnsxm65 said:


> And the lesson here is - buy mowers with Honda engines.


Norton Industrial F12 (*) FTW!! Mine's forty years old and still running.

BugBear

(*) AKA BSA "Sloper"


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