bmp01

Huh ! Mine too. Thought it was the filler cap but I'll check this .... bmp01

I think it will be good too. Update when it's done please. DT's, that brings back some memories. I had a secondhand125 air cooled that came with an aftermarket exhaust. On / off power band, noise, blue smoke, piston slap - come to mind. Happy days. There a rule about exhaust port width vs cylinder diameter. I wonder whIch side of the line your DT was bmp01

That's a whole big can of worms you're about to open. ... By the same logic you'd need to change inlet and transfers too, except with the inlet that would be adding material. And in raising the exhaust you are effectively undoing the compression ratio increase. I think if you are contemplating that level of change, rather than blindly following the manufacturers spec you would be better to aim for a known tuning spec, which will be driven by opening and closing timing (angle in crankshaft degrees). Folded into that you need to look at port and passageway areas....... My going in point (with out research) would be to leave timing as it falls with the lowered cylinder, 0.5 mm isn't going to equate to very many degrees. Go wider on the exhaust port would be the next consideration. Exhaust is pretty torturous on these though. Also, consider modifying piston with chamfer to change timing - gives option of a 'u' turn as you can subsequently put std piston in. bmp01

Ok, let me explain it again. .... don't use the hammer to flatten those lumps. Get-it? Well, it looks shiny. Interested to see how it goes now. Regarding the starting thing, it is worth labouring the point as it's a safety thing. Its not the force needed to start the thing - I'm sure you will cope with that. It IS about how much the saw reacts to the the pull cord force. In this respect a lighter saw and especially a top handle one is worse than a heavy one, we all know that. But adding in the higher compression on a small saw really makes things surprisingly jumpy. bmp01

It's Shed tuning, Spud Not commercially viable granted, but fun for those that enjoy that sort of thing. But in fairness if you can run the piston up close to the squish band it will reward you with a little bit of extra oomph but more importantly an all round nicer engine. The turbulence you can get from tight squish is underrated IMHO, a more dependable / reliable combustion process due to the extra gas movement, so even if the mixture isn't spot on (it never is, through the whole rev range) - combustion will be better. So hopefully a more crisp engine response. Just makes the saw nicer to use. Innit.... Starting it might need a bit more care though, especially a top handle saw like this one - you listening MattG? bmp01

Mr Pierce, ye PM need a wee clear out too.... apparently. Anyhow, payment sent. bmp01

No change, I'd still like the 136 please. I'll repair yours with bits from mine or repair mine with bits from yours. I have no desire to hord parts so I'll gladly pass on what i don't need after rebuild. bmp01

That piston looks good. The one i have was grey to black when viewed from exhaust. I recon it thought it was a "double acting piston" with combuston above and below The ring came out in three bits, broken either side of the locating pin. Don't think JB Weld was gonna fix that. Does yours feel like it has reasonable compression? bmp01

ooooh, please, if it has a good piston i could make use of that. The one i have in bits has a broken ring, piston written off blar, blar. PM inbound Thanks bmp01

Got any double sided tape? You want the stuff that is just a bit thicker than normal sellotape. I've got some made by 3M and some used for carpet laying, both work. When you need to remove it, use heat. The key here is a uniform thickness of what ever you use to hold the paper. Yeah, i understood how little you need to remove. I don't think you even need to go very coarse (200 grit?) but cleaning the paper and cylinder regularly to stop it "plugging" will help. And of course none of this is worth it if you make a mess of the cylinder bore so keep the bore and piston OD clean. And keep the paper away from the edge of the piston, say 1mm minimum in from the edge. Just my 2 pence worth.... bmp01

Emmm....not sure about that. On a 4 stroke (what i know best) running lean definitely causes ext temp to go skyward. As you go lean, combustion slows down. Slow combustion means you get less energy converted into mechanical energy - imagine the extreme case where the bulk of combustion is taking place as the piston is way past tdc and travelling down the cylinder, you just dont get the cylinder pressure at the right time to do any good. And if you don't remove the energy from the gases they stay hot - so higher exhaust temps. Pistons and exhaust valves also get toasted. It's got to be the same with a two stroke. Plus, and maybe more importantly the higher engine speed you get with a lean engine means 1) more combustion cycles so even if every thing else were equal that's more heat to get rid of and 2) combustion takes a finite time so at some point the engine is reving too fast for the engine to be efficient (just like the running lean logic above)... and that's more heat out the exhaust. Conversely a bit of extra fuel - running rich - the extra mass of the fuel absorbs some of the combustion heat causing cooler combustion and a cooler engine. I know which I'd rather have. bmp01

You not planning a life in politics then ???

So is this the MS230, that wouldn't run. ..the one where carb had been visited by "Bodger's Inc" in a former life? If i were you I'd do some searching on how to tune a carb before you do much more with it, there is a real chance of damage if its running lean (and therefore hot). There are some good You Tube videos on the subject, you need the soundtrack as tuning is done by ear (or with a tacho if you have access to one). bmp01

So get a bit of sandpaper stuck on the top of the old piston, spin the piston with a bit of wood. 5 mins and those protruding lumps will be gone. Use the existing squish band to guide you in your progress. You're not afraid to get in there and clean up the combustion chamber, this isnt much different. In both cases very careful cleaning required. ... bmp01

CNC lathe.... surely? bmp01

Yeah, Dremel isnt a precision tool, i was assuming you'd blend to surrounding to create clearance not an exact squish number. Have a look at Mastermind's squish machining technique on Arboristsite. He uses a single profiled cutter mounted on a sustitute piston that closely matches the bore size. .... hand operation IIRC. Or for the material you need to remove - sandpaper mounted on the end face of a piston / sustitute piston (end face or piston not flat). By the way, are the 4 lumps lower than the squish (that really would be carp) or is the piston domed? bmp01

Agree on all counts. MS200 has a nice little connecting rod - not much stretch in the two bearing bores, unlike say a 1 1/2" or 2" (38 to 50mm) bigend ... 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