bmp01

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

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 ?

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 ?

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.

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.

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.

"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 ....

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.

.... plastic not metal.... fair enough. Its just to stop the rubber manifold from collapsing in under closed throttIe vacuum.

No12 is a metal ring that plugs into the rubber manifold. I think its no 5 - which seals the reference pressure on the metering diaphragm to the pressure in the air box. Otherwise it would be referenced to atmosphere, (how older saws are). Its a simple dodge, to try to correct fueling when the air filter is partly blocked. Cant see it making much difference at idle, clean filter situation. So, fuel in the pump but not the metering side eh ? Obviously you did get fuel in metering side (on choke) or it wouldn't have run at all. Then again saws been stood for a few days so maybe evaporated off, not conclusive.

Added a bit more to that post as an edit....

Metering arm lives under the metering diaphragm, requires the carb to be pulled apart... IIRC its a Zama carb on these, the Zama website is quite helpful if you can tolerate some reading and pondering. There's a full explanation of how the carb works on choke, part throttle and open throttle plus the pump and metering arm layout. ... Head to http://www.zamacorp.com/ then look for SUPPORT, then TECHNICAL SUPPORT then DISSASEMBLY AND SERVICING (types C1U etc). Down the page you'll see this: It used to be you could download this technical guide, not sure that's possible now. Anyway, that's the metering arm stuff, you need to decide if it's the type A or B, can't remember. Whie you're in there, there's the filter to attend to. Pretty sure you can check the main jet one way valve in situe by accessing one or t'other drilling while closing high speed screw.....

Unscrewing the idle screw too far out will disable the idle circuit but you'd have to go a long way. If engine starts like this it will rev high - like the high idle position on choke switch. The pump in the carb is pretty straight forward, as you say if the diaphragm material is in good condition, correctly positioned against the carb, gasket against cover, then probably ok. You need the crankcase pulse signal to reach the carb but there's no separate impulse line on these, its combined in the rubber boot, worth checking for splits though. A few other things, -did you check and set the meter arm height in the metering side of the carb ? Maybe fuel is getting to pump but going no further, coz the metering valve is closed. Research on here, been covered many times. If you strip the carb after the engine stops (no choke) pay special attention to where you find (or dont find) fuel, it can help with diagnosis. -did the filter in the carb get changed ? Same logic as above. -main jet one way valve not doing is job, happens if an air line has been used to clean main jet. Check by bIowing each way through the jet with a piece of soft tube. -accerator piston and its oring worn out, needs removing and inspecting, happens on old or high mileage saws. Also been covered on here.

Second issue - doesn't sound like an issue. Once you have a bar/chain on there, sprocket will slow down much quicker. Side cover will reduce sounds too. First issue, yes carb. Starting on choke sucks fuel into the carb. The brief running off choke is using up the fuel that's now in the carb/engine. Either the mixture is a bit Iean - so as the excess fuel is used up the carb is not supplying enough fuel. Or the fuel pump in the carb isnt working, so the carb (and engine run out of fuel). Off choke the carb cant suck fuel up, so you need the pump... First punt, back the low speed screw out an eigth turn, try it. ...then try another eigth turn and try it. If no improvement your probably into pump issues.

Not sure if I'd want it to be working or broken at that stage, emoji is spot on.

Nope not what I meant .... although obesity seems another thing were not good at (or good at depending on your persective). In a nut shell, I meant we (in the uk) dont like to be told what to do, we dont like following rules or guidance (compared to other nations).

Read a few pages of this ..... Seems to me there might be a correlation between the attributes of the free minded UK population and how well the UK is doing in this pandemic. Absolutely no point blaming anyone in authority (government or medical establishment) for not steering the ship in the right direction because 'we' pay no attention to it anyway. I'm not referring to individuals on here necessarily - but you can see it everywhere in society from the groups of teenagers 'behind the bike sheds' to the parents at the school leavers parties, the callers on the Jeremy Vine BBC radio 2, the beach invaders etc, etc, On this particular challenge it seems our society is not best placed to achieve a great result. Individuals dont have a unified goal or the will power to weather the isolation (or what ever the requiement is) and crucially we dont have the dractonian penalties of the communist counties where the control of people becomes easier. We're just set up different, good for some things not so good for this.

Interesting reading that Macpherson. I like the logic, worth a punt for me. I like that there is no product for sale (ie no financial angle), although I guess we shouldnt discount the author making a name for himself and maybe he has an axe to grind with established pharmaceutical companies. Turmeric (pills) is a natural alternative to conventional anti inflammatorys. Not saying its a replacement for stong pain killers as seems less potent, but has its place and helped me through sciatica and minor disk operation.

From my limited experience I'd say that's reasonably conservative cylinder pressure. Looks like you've gone for a small squish to get over the high exhaust port ( "97 degs ex" ---> 166 exhaust duration, big number). You dont get any piston to det band contact with that ?

Ok. Interesting point, what numbers do you use to say you've over done it? 220psi is ok for a works saw but I've not managed that. ..

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Flexhones are pretty harsh and not what you'd call precision items. Seen them used on 4 stroke engines successfully after some practice but don't think I'd like them 'balls on sticks' running across a port. At least with the brake hone the stones are tall enough to not 'fall' into the port. Just my 2 pence worth....