bmp01

Spud, don't be a cock, ye cocky 'ol cock ....

That's a good video, explains it well. Unfortunately the guy said 'metering diaphragm' once by accident when he meant 'pump diaphragm' , maybe that's what has caused confusion amongst respected members on here? Can't say I've seen 3 one way valves in the pump most have 2 flap valves. That aside, really good schematic, model and voice over.

Can't see how you can do that final cut without stopping the traffic ....

Wow ! Looks to me like like the cyclist was awake (before the 'event' I mean). Road position and leaning forward on the bike. Even so, there must have been a few extra heart beats ....

Stihl piston on the right hand side would be my guess ???

..... just turned blue reading that lot in one go..... ? But no sorry, no spare carb. Sounds like a fun project.

No it isnt. Depth is typically 0.025" (and not 0.25" as mentioned above). T'would be some scary contraption to rip a 1/4 inch cut per tooth.....

Yeah, we should be..... talking thousandths.....

Good point, that's a pretty awesome fact too. 72 bpm, (resting average heart rate) to 70 years old. .. ----> 2650,000,000 beats Active person might be more although at rest heart rate probably lower than the average.....

So what are you saying here ? Why didn't the fuel lines you fitted at the start of this thread not fix the problem - bad material or wrong diameter hose?

Had a similar 'project' on my mind, I had concluded the sprocket material was chuffing hard, too hard to machine with HSS tooling. But you've shown there is a way, so what machine tool material did you use ? The sprocket I wanted to machine is one of them power metallurgy things, I think.

Its mind boggling the number of revolutions an engine will do. I just did a similar finger in the air calculation for a car engine. ... 100,000 miles in the engines life 45 miles per hr average speed ---->2222 hrs ------>133,333 minutes 2000 rpm average engine speed ------> 266,666,667 cycles Pretty amazing you can have bits of metal rubbing against each other and survive that number of cycles.

I picked one of these up recently. It was a curiosity thing, 12 quid to have a look, so..... Non runner reasonable compression, and spark. 2 out of the 3 chains had been used - the guy probably got his money out of it. In this case the problem was with the fuel line, it was in two halves. Hose material was complete shite, utter, utter shite. So it works, cuts wood ok - i guess. Maybe i got lucky, it was a simple fix for a few penny's. But then again maybe not, I don't think it will be long before the quality of some other bit causes bother...

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.