bmp01

A round file in one of them guide thingees to get the depth right as you’re new to it. And a flat file and guide to take down the raker height. And a pair of reading glasses for me, these days 🥴. Don’t underestimate the benefit of seeing the cutting edge of the tooth in all its glorious detail.

Ask for copy of work shop manual on Outdoor Power Equipment forum, members there go out of their way to get hold of manuals and share them….there might even be a dedicated section for the purpose, can’t remember. Elec saw might be a challenge but if you don’t ask you don’t get.

Picture paints a thousand words… impulse line location and swap, have a look here, at 1/4 - 1/3 of the way in.

I think that was the plan until Openspaceman found that the coil had stopped sparking all together (going by the posts above …)

Sounds like progress 🙂 thanks for the updates.

….best on no choke…. What does that mean? I bet it means choke for a dozen pulls, frustration, then trying every other control switch option….🙂🙂🙂 Or am I wrong and it means no choke from first pull? Have you tried 3 pulls on full choke then switching to ‘half choke’ irrespective of it popping on full choke?

A bit of history with that saw then. Aftermarket coil rings alarm bells for me. What about a strobe light, could you use that at pull cord speed to see where it’s sparking? Does the flywheel have features to pull it off nicely - I expect Spuds workshop manual (posted earlier in the thread) would tell you.

Maybe but I’ve not owned one so can’t add detail, sorry. Could be a few different flywheels/ coil combinations to mess up timing…. I guess you’ve tried Spuds bend the plug terminal to get the spark to jump bigger gap…establish if coil is really healthy (not just pretending ) ……. heading off piste here aren’t we…..

That was my understanding too, just wondered if Pleasant knew different….. it was 2023 when that message was posted, I’m sure Esso have had to toe the line….

The Esso fuel being zero ethanol in the past, is it still true ?

Nope. Turning the screw clockwise is ‘closing the tap’ - saw will run leaner. In your other comments you said turning screw counter-clockwise helped the saw run better (for a bit) - in this case you were adding extra fuel …. It’s likely the extra fuel is helping compensate for an air leak or an issue with fuel delivery. Be cautious, find the cause for the original failure before it repeats. I know this is repeat advice, Stubby, but…..well… it’s right innit.

😆 ....sharp intake of breath.... did you just 'dis' a Stihl ? 😨

Well, saw is fixed with the new carb so its no longer going in the skip - thats a good thing. As for the above - I agree with what youve said. Ref the video of it: - Most saws die on choke with over rich mixture (not all, but most). - Didnt revup properly once throttIe was opened, think it was just spooling down from there with out any more combustion. I dont think it had a full metering chamber of fuel (after runniny on choke), I'd guess its pulling in fuel and air into the metering chamber while on choke and thats why it kept running (on choke) and didnt die (over rich). Its just that on choke theres such a high vacuum on the fuel circuit that even with an air leak there is still enough vacuum to pull some fuel though. Either that or the diaphragm's too stiff or wrong version and just not operating the metering arm. But anyway all somewhat irrelevant now.

The fact it wasnt running right since the last bad repair hasnt stopped the guy from using it - judging by the chain imprint (wear) in the spur gear teeth. No sense of mechnical sympathy = bigger repair bill.

I presume it had the rails with it ? Works ok once rails are set up on a straight plank, just a bit of effort to get to that stage.

Might be the picture, dunno, but that metering arm looks a tad low ? Quite a jaunty angle too, I'd be tempted to tweek it up a bit and then bend the contact face so its parallel to adjacent carb recess, maybe Im a bit OCD ??? 🙄

Always nice to be completely sure about its itegrity and tick it off the list of suspects. Onwards.....

You dont need the purge line gubbins. I'd argue youre better without and have deleted it many times on my saws. Just put a short bit of hose on the carb (in place of the purge hose) and blank the end of short hose. Blank off he purge line too. So long as that oneway valve passes fuel without restriction your now good to go. Regarding the main jet/one way valve .... small parallel punch and hammer.....tap it through into the centre of the carb. I hold the carb in vice jaws with the choke in closed posn, bit of something soft to protect the faces of the carb. Keep the punch in the midldle of the jet. The jet will pop out into centre of carb, you can retrieve and inspect jet for its one way operation. Also have a look at the drillings in the carb and the groove around the jet and see how far the jet should be installed. Just tap it back into place when you're ready, it alignes itself easily with a little care. Theres no rocket science here.

I agree with adw, the check valve (red circe) is to stop the purge bulb from sucking air through the various jets - its so much easier to suck air than fuel. Where's the fuel feed to the low speed circuit ? Is that through the same check valve (red circle) as high speed circuit ? Also agree the brass main jet looks odd, looks like its pressed in too far. Does it protrude a long way into the carb throat?

How many times do you hear a lawn mower running out of fuel, starting to hunt up and down and think to yourself just stop it and refuel. But no, they keep going until it completely dies, then after a few minutes there's the sound of a pull cord being pulled over and over.

Yes. The carb is for my toy chinese top handle which was in need of help when I got it. It was cheap as chips so after making it work and being utterly upset about how crap it was in standard trim its been though some changes. Runs great although I might have gone a tad too far with inlet timng. After that I was pursuaded by a Bellhopper video that increasing the carb size was a benefit and as part of that I moved the check valve opening towards the edge of the venturi where air flow shouId be higher. It all works fine although in all honesty I cant tell any difference in the before and after carb mods. But yes, the check valve survived being opened up, shortened some and swaged back together.

Yes, although the little retainer disc with its castlations faces inwards towards flap disc so less surface area to stick to.... if sticky is the issue....

Wonder cure probably not, cant fix broken. But carb cleaner isn't either, useful but not a cure all. I thought 'super' unleaded had some nasties in it that helped clean ? Add in a running engine ie vibration and heat plus exercise for the carb - you never know. Could be completely wrong here, its completely subjective, often feels like an engine thats not been used for a while goes better on day 2 of use. Might be softening of metering diaphragm, change in the weather or sumtin ? 😒

Point taken. My last input on check valves then, its gonna change your thinking though ! Picture below is a check valve in bits, its from a chinese carb, I was messing about with it at the time. But they are all the same. The point is .... there is no spring (or equiv) holding anything closed. The little flapper disc moves open or closed with the breeze. Like a reed valve but with zero bias.

Yes I agree it does divide the carb. I'd add this: At low speed (low throttle openings) the check valve closes off the high speed circuit completely, engine is fed from low speed circuit only. At high speed both the high speed and low speed circuits feed fuel to engine. I suppose a test for this might be to some how get the engine runnIng at a decent lick and close the low spoed screw. Look for a high no load speed.... Im gonna have to disagree with you 😨 with what happens if the check valve gets stuck open. While the throttle is closed there is ambient pressure at the high speed opening in the carb inlet port so no means of pulling fuel into the carb inlet. I suppose there might be some vacuum in the inlet port if the air filter was monsterously blocked.... just like the choke does. Edit: Actually rather than worrying about what we think is giong on with presures and all that, just have a look at the check valve in the flesh as it were. It only checks the flow from reveresing. It does not stop the flow in the forward direction, that is to say fuel flow in forward direction is the same if the check valve is operating correctly or if it is stuck open.