bmp01

Tiny bit more. But can be done at the same time as the existing squish and cylinder bore machining. No reason why the CNC cutter path has to machine the squish flat either. bmp01

It should be, it's a machined band, cut at the same time as the boring opertion. Disappointing to hear the combustion chamber of MattG's 200T has lumps in it, presumably in board of the machined squish. Time for Dremel work? Equally disappointing the squish is in the 1.0 mm range, poor effort. bmp01

Is the 200T subject to the same sort of tolerances as the rest of the range or do Stihl make a special effort on these? How about shooting for 0.45mm (18 thou) as a starting point for your mods bmp01

If you take a std Stihl carb and disable the accelerator pump, what's the difference between that and a Stihl carb that didn't have an accel pump in the first place? Was it anything obvious? I can imagine more drillings into the carb port (close to the butterfly) fed from the low speed circuit. The jet for the low speed circuit may be a different size too but that's so small i don't know how you'd tell. bmp01

Hello, Glad you got it sorted. Did your diagnosis include taking the old carb apart ? Accelerator piston scored and O ring undersize ? No ideas about the life of new carb. Does that have a accel pump in it? bmp01

Or if you have enough thread you could loctite a grub screw above the correct screw. That assumes its proper engineering thread in metal, not some self cut thread rubbish. bmp01

Epoxy, JB Weld. There are fuel proof versions which should be ok with oil. I presume its just to seal the leak and there's no structural implication. Somewhat awkward to find in UK, i got some from Opie Oils when i was buying oil for the car. If you can access the holes through the filler cap you might even be able to do the job with out disassembly, I'm thinking several flushes with fuel and then degreaser like brake cleaner.... unless you want to take it apart again... bmp01

Yeah, we can add a second line to the expression... "If it works, don't **** with it" Such as, "But if in doubt, rip it apart" Works for me bmp01

Another vote for pull cord rope stuffed in the cylinder - i like the idea of distributing the load with something a bit flexible, much like what the running piston sees with combustion pressure. A solid piston stop is the direct opposite. bmp01

Result ! Thanks for the update. Soooo, why did tightening the bar nuts cause the chain to not run smooth? Do you think it really was an alignment issue between the sprocket and the bar - because the sprocket had restricted sideways movement? Or simply the wire getting into the rollers of the needle bearing under some conditions? bmp01

Inside the tank I can just see the ends of the studs, as in round, end of a thread. But actually i don't think the studs can put any sideways defection in the bar / cover. The shoulder on the stud would have to be unwound about 5 mm before it stops the cover going on. You can see in my pictures above there is a recess in the cover, for the stud shoulder to pass into if indeed it were far enough out to come through the bar. Your picture is showing the studs are either screwed right in or almost all the way in. bmp01

Just been out to take the cover of my MS260. Got another idea for you what about the nylon chain rubbing strips pressing on the chain? Have a look at the attached pictures. The nylon strips are pressed into the cover, but they are pretty loose. So easy to remove and easy for wood chips get behind them and move then out against the chain. ... I think that would cause a little bit of drag on the chain. bmp01

It's not obviously out of line but we're only looking for a fraction of a mm, can't see that in a picture. Put both bar nuts on the back stud, lock the nuts together then try to tighten the stud into the housing. If it moves you know it was loose. You'll have to remove it and loctite it in. Repeat on the front stud. ... bmp01

Sounds like a diagnosis. Have to wait for new sprocket to make it conclusive. The bolting it up thing is a puzzle though. It sounds like the wear pattern is not in alignment with the chain but that would imply a change in the position of the bar or position of the sprocket. Even a spur sprocket can move a little so youd have to be out by quite a bit. And youve changed no components? Couple of other things to try... -Assemble the saw with the bar but without the chain, tighten down the side cover. Does the clutch still rotate freely? I'm sure it will but worth the time it takes to check. -Back to normal assembly - If loose chain tension makes no improvement (it should have), maybe its nothing to do with sprocket. Are you pinching the chain drive links between the bar rails when the cover goes on? I know its across two bar and chain assys but are they all std components? New or old? Any damage to bar rails or where the chain enters the bar? Is the the clutch cover flat? Whats the wear pattern like on the clamping faces... that sort of thing. bmp01

Yes. Just so long as you don't get one of the ones pileswasp and eldon are on about

What we're the symptoms with this 'off centre sprocket' - a description might help the OP to determine if it's the same issue. I can imagine a frequent tight - loose - tight - loose etc type feeling as the chain is pulled round.... bmp01

Doh , I missed that. Thanks for highlighting it. 2 excessively tight spot chains then Actually, lets see what the result of loosening the chain is. Also, If the chain tightens every 7 drive links (one rev of the sprocket) then sprocket is at fault. bmp01

Back off a bit more, you don't need to run it like that but let's see what happens, you might just have a chain with excessive tight spot ? On another subject i had a cheap pole saw that was going tight and clicking, turned out 3 or 4 of the drive links were burred over at the edges. Was an Oregon chain, 90 % good links, and almost new. Needle file, burrs removed and all good....well, as good as it was going to be. bmp01

I guess you've tried backing off the chain tension a fraction and got same result? bmp01

Nope hand reamer, just to remove scoring, so oversize by 0.2mm say, reamer cost insignificant over 10 carbs or more. Batch of pistons, in plastic not plated brass, fiver each.... even if they were 10 quid each, your still saving heaps over a new carb. No use to me though, every saw i look at is different ! Working accelerator pump might be as manufacturer intended but the whole arrangement is a bodge to allow lean idle for emissions purposes, isnt it? Fold in the amount of PITA engine behaviour you get when the thing inevitably misbehaves and I'm all for deleting it and run idle mixture to give good engine response. My experience is over approx 10 carbs (various engines) so no way is it conclusive. Totally accept your point re MS200T engine response too. bmp01

Ok - you know better than me. What's the alternative though if the accelerator piston and its drilling are scored? -New piston and o ring is a temporary fix at best. -I guess you could ream the drilling and make a bepoke oversize piston, actually that's quite realistic if you do loads of them. -Or punt for replacement carb.... minefield - cost vs quality ... bmp01

Ah-ha, 201 is a strato saw, no way the carbs are going to be the same then. I'd go with blanking the accelerator piston circuit on the original carb then. Nothing to loose, you can always get a new carb later. ... bmp01

Don't suppose the carbs are inter-changeable between the 201 and 200 are they? Would be good to swap a known good carb on to the 200 .... bmp01

Don't want to pi55 on anyone's bonfire...but....the lever being 2mm too high - that would have flooded the engine (direct opposite to what you experienced). I bet there are more gremins in there somewhere and someone tried to cure the symptoms of no fuel by wrongly adjusting that lever. Personally I'd go through the rest of the fuel system and make sure it's right. bmp01

This is well worth a look, Zama Technical Guide. You'll find the setting info for the metering lever in there. http://www.zamacarb.com/pdfs/TechguideSO.pdf&ved=0ahUKEwiUlZudk7XTAhXIJlAKHb3RD18QFggeMAI&usg=AFQjCNGLlvPYMb6LZUNDqoT_UovEWcER1A Just one question, that silver cross head screw inside the metering chamber, does that look messed with - has someone been in that carb before? bmp01 Edit - metering lever looks like it is very high in your picture, is that just the cameras perspective or has that been messed with too?