bmp01

Presume it's a standard piston  (not aftermarket) and there isn't a mega amount of carbon on piston or in the combustion chamber ?

Thanks for the update Dinosaw. That's a real puzzle then,  but as it has the standard side cover at least that explains why you can feel the compression cycle on the starter cord - you would not feel it with easy start side cover. 

How about the side cover has been swapped to a std one but they fitted a starter pulley from a different saw - a small pulley requiring more pull on the cord to give the same torque on the crank ? Maybe the easy start model has a smaller pulley ? Bit of a punt....

38 minutes ago, Stubby said:

Does the chain go round when you pull it over ?  Wonder if its a rusted up clutch bearing ???

But it pulls over OK without the plug in. .... that's where it gets confusing. 

Have you had a look at the thread "MS211C weird problem", different machine obviously but same problem....

On 27/09/2020 at 10:11, Dinosaw said:

 Going to dismantle it this afternoon.

Find anything out of the ordinary ?

5 hours ago, Khriss said:

..... Any way,  bought a leaf blower after decades of not wanting one-  so will test n report back. Wots sauce for the Goose is sauce for the Gander,   Mr @Stubby will see how they like their frappe with extra sprinkles.  K

Muffler mod it ? ....

14 hours ago, Khriss said:

....... Gave this a think....  1 hrs leaf blowing with 25:1  once a week  = 50hrs.  (  My fvkking neighbour  ?)      dirttier than Ford doing  50hrs at 60 km/h    = 3,000 km is actually bang on ?  K

They said 30 mins of leaf blower not 50 hours....

Anyway its about how much fuel each machine uses. What's a typical L/100km number for vehicle? Lets say 5 (optimistically)......thats 150 L then. Leaf blower .... dunno.... 0.5 L max ? Ok so vehicles cleaner running with cat etc  but at least 300 times the fuel ... sounds like a croc.

And producing the fuel,  how clean is that ?

4 hours ago, Dinosaw said:

Definitely gets tighter as it passes the exhaust port. I thought that somehow some chain oil had got into the crankcase but it's been upside down for 24 hours and not a single drip. Going to dismantle it this afternoon.

Be interesting to see what's up with it. 

Still got my money on the easy start mechanism.  If it was working properly it effectively decouples the engine from the pull start - all you are doing with the pull start is winding up a biggish clock spring, so you don't feel the compression stroke. I bet it broke and has been bodged somewhere along the lines . ...

Google ergostart for utube vids demonstrating the easy start.

3 hours ago, Paddy1000111 said:

It hasn't been fiddled with before has it? If they left the cylinder seal off the bottom then it could pump up the compression by a tonne? Could even be touching the head? 

It's a clamshell engine - no separate cylinder (so no gasket between cylinder and crankcase). You can bump up the compression eg taller piston or change the crank centreline.

Is that the "Easy Start" model being the 'C' ? If so, it's got an extra spring between the pull cord and the crank....  I'd be looking there. Actually, I'd take that start cover off, toss it over my shoulder and reach for a standard side cover to try. 

7 hours ago, CEE said:

I dont know how this is happening becuase you can see the spark on the spark plug when it's grounded and I tested the coil at be 0.5 Ohms (the spec) and I have got a 0.3mm feeler guage and set the air gap...

Firstly, well done in sorting it out and not giving up. 

WRT seeing a spark, that goes to prove the test isn't adequate.  As stated earlier you need to get a spark to jump 4 - 5 mm in free air to be confident there will be a spark in the cylinder with compression. And when the coil and ht lead is put under load you might find the insulation breaks down somewhere in side the coil or through the side of the ht lead.

Or it might be the spark is good but the coil timing gone for a poop.

Anyway, it's the result that counts,  nice one. 

How long between the last time it was used and now when it won't start?

You'd put money it being a fueling issue wouldn't you. 

Try some easy start spray, should run for a few seconds and if it does then you can say ignition is OK.

Did you check the metering arm height when you were in the carb ?

The thing is,  using the purge bulb draws fuel through the carb but it will also pull air the wrong way through the tiny low speed jets (its why you always get some tiny bubbles in the bulb), i just wonder if the metering diaphram has stiffened slightly while not in use and if the metering arm height was marginal maybe it's the opposite to what you think and not getting fuel. ... just thinking aloud. ..  Nah,  that's cobblers; on choke the engine will stuck fuel through ....

But try the easy start.  And try the hot plug. 

That's bad luck should have picked up a clue with all your tests.  Couple of things to try, might help might not.

- heat the plug with hot air gun or blow torch till you need gloves to fit it. You might have evaporated excess fuel but that's probably left 2 stroke oil behind,  might be gunking up the plug, hot plug helps.

- a spark jumping a std spark plug gap isn't necessarily adequate when its in a cylinder with compression you want to jump a 4 or 5 mm gap. 

- timing might be off if the electronics in the coil are up the creek. Most coils will have an advance curve so it's retarded for easy starting and increases above idle for better performance.

- un route the ht lead so its in free air, if it has shorted to housing or wires etc you won't know it, you might learn something from trying the big air gap spark test.

- I'm guessing you've checked to flywheel gap. 

Keep at it,  sledge hammer might give you some satisfaction but it'll have beaten you if you go that route.

10 hours ago, openspaceman said:

I've been debating trying this on a stihk where the flywheel key has sheared but not felt courageous enough yet.

 

I'm guessing one must mark TDC and whatever advance it needs, assemble it and then use a strobe to check how close you get.

In my case a 395XP. Same thing sheared the key, didnt clean the taper, doh.

If you get lucky, there is just enough evidence of where the key was - so trial assemble like that to sort your alignment (use a piston stop and mark the outside of flywheel to some feature on the housing...or coil). If you're unlucky (no evidence) you need a machine to copy or as you say use a strobe and trial and error.

Disassemble. Use fine lapping paste to mate the two surfaces. Clean thoroughly. Repeat as necessary. Assemble dry or with loctite, epoxy, Devcon, JB Weld, what ever takes your fancy and dependant on how ripped up the surface is. Take care not to shift the flywheel as the nut is torqued up. DO torque the nut up.

I'm not inventor of any of this procedure - it's pretty common place for the US modders to want timing beyond the half a key mod. And of course Mr Spud here has fixed many a machine without resorting to new flywheel.

41 minutes ago, Stubby said:

God hates you . 

That'll be it. You been cutting down his creation again ???

21 minutes ago, SpannerRat said:

I don’t know the history of the machine unfortunately. Crankshaft is out and all looks fine. Can’t see any damage.
Thinking may be the wrong crank, can’t find any reference to the number 4159 031 1600 A so no further forward.
 

I wrote in my previous reply 'bet its a parts bin issue' then deleted it as it sounded disrespectful ??

Oh well, if the crank fits and there's nothing wrong with it you can always have a go at fitting a flywheel without a key,  use your other machine as an example for where the flywheel should be. Been there, done that,  haven't we Mr Spud  ?

12 hours ago, SpannerRat said:

The flywheel side is the PTO side on these, clutch bolts to the flywheel. The bearings looked ok when I slid the pot off for a peek.

Ok.

All the torque through one crank web and shaft then. Still a bit odd (for it to spin). Also I dont see how it gets to be so far out, should have stopped running long before then. Or did it have some bad event during its last run ?

11 hours ago, Mrblue5000 said:

bmp hot after cutting, oil is going out about 3/4 tank per tank of fuel and bar oil hole is clear.  Will have another go in the morning and let you know what happens. 

Sharp chain might be all thats required .....

Once upon a time I sharpened a Stihl mini picco chain with a file for a 0.325 chain, wouldnt cut a thing, melted paint off the bar etc. If your dumping 1/2 hp into friction things is gonna get hot. 

Does it get hot with just the chain going round, so before cutting anything?  Or only hot after cutting ?

How's the oil supply to the chain (after its time of sitting)?

Blunt chain and heat generated will cook the bar oil into a sticky mess.

If the chain fits in the groove in the bar and theres a little side ways play then thats all you need. 

9 hours ago, SpannerRat said:

I have a KM94 that’s had me scratching my head a fair bit. Has compression. Has a nice spark, but won’t fire or even pop.
Went through a whole range of options before I got there, bad flywheel?, bad key?
Eventually realised that the timing is way off. Still haven’t worked out quite how it’s ended up like it is.



Rouge one on the left, working on the right, both at TDC.

I can only guess the crank has spun on itself???

Would have thought it'd be the power take off side that would 'spin'. The flywheel would slip on the crank before the crank slipped.  Unless the crank parts were well out of spec when assembled.

Don't suppose it has done a big end or small end bearing leading to a load of backlash and confused the tdc position??

No doubt all well become clear when is apart.

15 hours ago, peatff said:

 

How can you remember what you've forgotten ? ? I can't even imagine how much I've forgotten.

You can't, that was the point....

Although occasionally, maybe when your fixing something for the 2nd time many years later, you think, "em - that look familiar" and suddenly that bit of forgotten stuff comes rushing back.

....on the other hand, I know I set the needle to bobbin timing on an old Singer sewing machine just earlier this year.... Can I remember the procedure, can I  **** !  Back to t'internet. Talking of which if I could just remember which internet page.... one of life's most frustrating things, trying to find an internet page you looked at before. And yeah I know about bookmarks....

Makes carbs and 2 stroke engines a piece of pi55 in comparison.

6 hours ago, spudulike said:

Bloody hell, just get on with it man, sleep is for wimps, there are 24hrs in the day........failure is not an option

I was saying to the wife the other day that you forget how much knowledge you acquire over time and it is only when you tell someone how to do something you think is quite simple - fit a bar and chain for instance, you realise some know nothing and how much info you have accumulated.

 

"you forget how much knowledge you acquire"

Ah, but can you remember how much knowledge you have forgotten over time ??

Nope, me neither.  

Optical illusion ? Or time to visit the patent office....

Have a prod around with a piece of wood or plastic, bet theres a ring or 2 in there .... 

13 hours ago, spudulike said:

The only thing I would say is that drifting the check valve out is sort of simple but it is fairly unlikely to be the issue. It gives a saw a real lumpy pickup and massively over rich running - I do around 2-4 a year and isn't a common issue.

Re one way valve in main jet,

Frequency of failure dependant on carb abuse with airline.

Massively rich is coz the user tries to compensate for the broken low speed circuit by dumping in more fuel via the adjusters ?

I think it goes like this,  with factory set fuelling the saw will not run (or runs badly) at IDLE, coz some air going thro' the carb does a detour - goes wrong way up the main jet, through the metering chamber, out through the low speed jets. In the mean time the metering chamber cant do its job either.... The obvious thing to do is give it more fuel.

High speed with no adjustments all is well, but with adjustment to make low speed work it becomes rich.

Innit ?

Personnally once the carbs out of the saw and for the effort involved (not much) I'd be checking one way valve, if only to tick it off the list.

My money will be on the accelerator piston but thats a bit more painful to do. 

Title of thread was the starting point.

Blowing outside of carb clean is fine, to be expected on a well maintained saw.

What some folk do when blocked internal passageways are suspected is to whip the adusting screws out, pop the airline  nozzle tight against the vacated hole and give it "what for" ..... that's not the best thing do.

So, this is what I've done to test main jet one way way valve: Carb off, metering cover off, high speed screw out. .... soft piece of hose (silicon is ideal but small bore fuel hose is ok) over the adjuster screw hole, now health and safety aside, blow through the hose. You will find the fuel feed hole (below the diaphragm) let's air escape so figure out which one it is and block that with a finger (from your pictures there are 3 holes I think you want the one without a brass jet, but could be a second one too).  Now,  blowing and sucking through hose should allow air in but the one way valve should seal and stop air returning. ...

Aternatively attach a hose through the middle of the carb and onto the exit end of the main jet, same blow suck routine but expect results to be t'other way round. I suspect this approach is neigh on impossible due to size of the carb, unless you want to remove the butterfly valve...

Alternatively 2, to be 100% sure, remove the jet and test out of the carb. Its just pressed in, pretty easy to drift it through into the middle of the carb with an appropriate parallel punch thats in good condition. Hold the carb in soft jaws in a vice and take care.... I've heard of someone pressing the jet out on a pillar drill using it as a press. NB I've done this on a 211 carb, pretty sure there is just enough space for the jet to come out into the centre on the carb....

Main jet has its own Stihl part number and is completely replaceable, go by your pictures for how far to press it back in.

Now, I know Spud is going to hate me for going on about accelerator piston getting shagged but it happens way too often IMHO. IF the accerator piston is shagged its a source for air to get sucked into the meterring side of the carb. The accerator circuit feeds the mainjet too, so if its shagged that's going to throw your result in above first way of testing one way valve. Anyway, lets see how you get on.