bmp01

Think I'd like a middle support too. I quite like the set up. I don't there think there is a big difference between sturdy rails and a ladder. Twisting a ladder is pretty easy, the sides are not that well attached to the rungs. Steel is obviously stiffer than aluminium .... I wonder if the chap has some means of stopping the rails from travelling down the length of the trunk with gravity and the vibration ?

+ 1 With particular emphasis on getting the cord to do a lap of the piston - spread the load as much as possible.

Turning it back wards against the starter mechanism/cord ? Was it a sharp stop or did it have a bit of sponginess to it ?

Ya. That was my starting point too, then ...... way too many options. Saw looks clean, low hours I'd guess but what's compression like when its hot? Pick up the saw by the pull cord - does it drop quickly unwinding the cord or can you pick up the saw and watch the saw drop slowly as the pull cord unwinds through each compression cycle? What are you doing with the choke and fast idle when you attempt to start from hot? Get a new spark plug in it. If you are testing for spark you need the spark to jump a 3 mm gap in fresh air, do that with cold and with hot engine (heat soak the coil). If you can't come up with a scheme or tester use a known good plug and bend the outer electrode to give the 3mm gap. What happens if you drop a tiny bit or fuel down the intake and try to start it? Something to be going on with.

Uh ok.... That probably happened when you pulled the cap off, you've just finished it off stretching it to put it back on. There's always Mr Spud's repair service by mail if that saves you time and expense, I hear he likes to see a clean saw now and then.

There is a right and wrong way. ... First easy thing is to look at the throttle shaft and the throttle plate for the shadows and clean patches where there has been exposure to /air and contact between parts respectively. Looking at that throttle plate, the hole on the shaft should have left a nice tell tale circle on the shaft. Secondly, the outside 'diameter' of the plate isn't perpendicular to the plate surface, because in the closed throttle position it's slightly off 90 degrees from the port centreline. HTH

Breather just let's air into the fuel tank - so you don't end up with a vacuum in there as the engine uses the fuel. Completely blocked and you'd not restart the saw. ... partly blocked, maybe Quick and dirty test - no fear of breaking anything - run the saw up until it misbehaves, switch it off, undo the fuel cap, fuel cap back on, start it up and retest. If you can, try to note what happens as you open the fuel cap, air being sucked in or expanding fuel being blown out. ... Also worth noting a blocked (or part blocked) breather gives different symptoms with a full tank compared to a nearly empty tank. It'll be quicker for you to do the test than it took me to type this ?

Smart-arse , I thought we were clear of journalists type misquotes on here ... 'electronic raquet zapper' then just for you Yournamehere. Interesting point though, bats vs wasps, purpose vs agrivation ???

My wasp lesson was taught to me as a youngster at a french campsite. Drinking from a nearly empty fruit juice carton that had been left out...... Live and let live but killing the odd one or two that become troublesome is alright in my book. Electronic bat zapper ('moderately tuned') doesn't seem to encourage others to attack.

This spark tester goes in series with the plug then ? Does it work if the plug has a short inside it ? I've posted before. ... only ever seen a failed plug once and it was with one of these little plugs. See picture, this is a plug with an internal short, you can see the lines where the arcing has occurred. Get a new plug (or 2) and careful how the wrench interacts with the plug. ....

Coil to flywheel alignment across the face of the flywheel (not the 10 thou gap) ? Have you got the plastic spacer between coil and engine? Try another new plug too?

Accelerator circuit is for response during. ... wait for it. .... acceleration (ie increasing engine speed). In the steady state of wide open throttle it does nothing. You can understand this when you've seen the bits in front of you - the piston doesn't move any further once the throttle shaft has reached wide open throttle. ... So all you are trying to over come once the accelerator circuit is disabled is that initial stumble when you quickly open the throttle. I set the saw up a little rich on the low speed circuit. So at idle, find the fastest engine speed with the low speed screw, then back it out until idle speed drops slightly. Blip throttle , check for response... Worth noting, at operating speeds the low speed circuit is responsible for 25% ish of total fuel to the engine. So there might be a requirement for a small tweak to the high speed circuit. (That 25% number came from Zama website, sounds very approximate to me, but the principle holds). But let's not get too far ahead. Check the condition of the accel piston first.

Nope, my normal approach is to chuck the accel piston, make an ally plug to stuff in the hole and retune the carb. ... so far so good - I've not needed replacement carb. Yes it's a Zama carb as std eqpt. If you have an after market carb that probably doesn't have an accelerator circuit at all. The whole concept was necessary so the manufacturers could run a leaner mixture (for emissions purposes) with good throttle response. Aftermarket carb manufacturers are not subject to the same emissions legislation so they don't bother. Quality and life span of aftermarket is questionable by all accounts.

Yeah, it's not obvious is it. .. The throttle shaft (the one with the butterfly valve) .... where it goes through the carb housing isnt round it has a flat machined into it. That operates on the accelerator piston, which is buried in the carb body. Wish I had a picture. ... but anyway, if you look at the face of the carb, engine side, there is a hole parallel to the inlet port, 5 or 6 mm diameter. Sometimes they have a blanking plug. You should be able to see the throttle shaft running across the hole, you might be able to see its not round. So boringly you've got to disconnect levers, springs, butterfly plate etc and slide out the throttle shaft and the accel piston will pop out. It has a small spring behind it. Usual precaution, take some pictures, lay out the bits in the correct order etc so you can get it back together. You also need to be able to align the butterfly on its shaft and re-peen the end of the butterfly securing screw when you reassemble... If the accel piston is tired the plating is usually worn through see piccy. Worn o rings are often visibly small. Trouble is once the piston is worn there is a good chance the housing is too. The next alternative is to disable the mechanism, seal up the hole and retune the carb a bit richer. All in all - not one of the easiest jobs and time consuming. That's why they would just lob a new carb on at a dealers. HTH, if i can clarify anything just ask.

A proper scammer would have disappeared over the horizon as soon as they had your money, surely ? I can't see any reason they'd hang around ....

Low compression doesn't usually cause random behaviour. If this random behaviour happens even when the engine is warm then my guess would be the carb. You say you've put new gaskets in but did you check the accelerator piston o ring. It's boringly frequent that this little carb feature causes random behaviour. If you can swap in a known good carb that will set you off on the correct path of fault diagnosis. Presume you've tried a new plug, unlikely to fix it but as its easy ....

That's an extract from the Oregon Products pdf file I had in mind. I have it located but at 75 mb I can't post it here,.... Not sure it's needed now anyway.

I have seen an Oregon products guide which had all the different versions of bar mounts, dimensions and all. Just had a look on line, can't find it. I might have a copy on a computer somewhere ....

I reckon thats the answer , give it plenty of welly. If it's not too late take the plug out at the same time as the exhaust is off, lower the piston and you'll get a chance to see the combustion chamber, piston crown . The extra daylight helps a lot.

Picture of the plug with the carbon stuck in it would have been good, one for the library that. ...

This "hard carbon" you mention, are you saying its a lump of carbon that's maybe come off the combustion chamber and has wedged itself between the plug electrodes ? And its done it twice ? On the other hand fouling a plug to the point where its completely carboned up within the space of one tank of fuel is pretty much unheard of too (with modern oils).... Maybe it's just cleaning itself out after previous misuse, it might also be spitting carbon out of the exhaust too, just thinking about the spark arrestors on saws in USA.

Let us know where and when, we'll sort out some backup ! Maybe we could do a nationwide test day or something, that ought to be popular. ..

2 stroke oil is probably the thing that has developed more than the 'bits of metal'. So use decent oil at 50 : 1 (and carp oil at a higher oil ratio if you must). And if the saw starts screaming (high revs) get it retuned / checked out. If you don't expect too much from them and use a narrow kerf chain they are fun saws. Older ones are better than later 170's, so they say.

Bought 2 of those Lidl folding saws for the children to stop them from playing with my Silky Zubat - and to teach them how to be careful with folding saw . So I bought those ones over a year ago and i can see some differences to the one in this post but i have to say they work perfectly fine, they certainly don't jamb in the cut. And for the price, fantastic. Worth cherry picking the best looking blades.... In contrast the Lidl full length pruning saw (from a year or so ago), had teeth 'set' to cut a wider kerf than the blade thickness and looked cheap and nasty.

......don't they have some decompression mechanism thingee on the valve train, for easy starting. ....? That's from memory, I could have imagined it , but if true how would you know if the compression was low? Can't see why they would wear out the cylinder or rings unless mega mileage, no ports to worry about. The one i looked at (a non starter) - one of the push rods had popped out of the tappet due to clearance issue. Put it back together correctly, started like there was never anything wrong with it. Don't give in yet