bmp01

True enough. On these engines the reverse airflow is controlled by bottom edge of piston closing the inlet port. You will get a bit of reverse flow. A worn piston will make this worst - which is why Spud says check engine wear....compression test. .... You can check the one way valve in the main jet with the carb on the bench. Take cover and metering diaphragm off, blow and suck through the high speed passageway using a soft piece of rubber tubing, its quite obvious if one way valve is defective.

The 10000 sales thing - do you know if that's a fact ? Reason I ask; I've been on their website - every item they sell supposedly has sales numbers in the ten thousand region....and feedback of single figures. I don't believe they make, let alone sell, 10000 ms180 clutches (or what ever it was) but of course people do (believe it). And through internet whispers it appears to become fact.

TFFT !

Yeah, running fine for 20 mins is way into hot running..... anything beyond 1 min of running (under load) is hot. Sounds like plugged accel piston is OK. Areldite under the welch plug ? ? ? Surely not..... After 20 mins there's plenty of heat soak, hoses, intake boot, engine mounts all get a bit softer. Have you tried another quarter turn on the low screw when it misbehaves - might give you a clue if its definitely a fuelling issue. How long does it need to cool down to then operate correctly ? Edit: Could be the diaphram or pump in the carb need refreshing after that time sitting around in garage. Just thinking heat soak into the carb is changing their behaviour and therefore the fueling after 20 mins ??

And you've re-tuned the carb ? What did you do to disable the accelerator circuit ? Are you 100% sure its an air tight seal ?

Not you Khriss, had a chat with Mr Punk via messages.... I'm well beyond the "before you know it" stage.... Need to find a way back. .... which in the first instance means not adding to the pile.

Interest withdrawn, thanks for pointing out the error in my ways mister ?

Yes please, could do with a few spare parts off that. ... Edit, Message sent.

And how do you imagine you'd deal with a service shop repair where the replacement piston comes from a batch that was significantly different to the original batch ? Or how would you get over saws running on pi55 poor fuel (low octane) when all the saws come pre-tuned from the factory ? Plus a million other exceptions to the saw being run in its correct operating window. The thing is the manufacturers have been at it for a little while, they've done a few iterations by now and they know where they are in terms of tolerances, performance vs risk etc. They've forgotten more than you or I imagine we know. And no doubt they'll continue to hone the product with each new iteration for the end user to marvel at, not forgetting they are in the game of competing to sell better kit at each model change and at an economic price.

No I haven't. Got the little top handle one though, came secondhand broken and for cheap. Came with the original 4 chains. ... no doubt that means the chains are poor quality. If i was going to use it regularly I'd get a decent chain for it. As it is, its good for giggles every once in a while - opposite end of the weight scale. Its as cheap as chips but it cuts ok for the cc's.

My thoughts exactly. Saws don't start struggling, if it was ok to start then either the woods got bigger/harder or saw maintenance is lagging whats required. No 1 on the list will be "how sharps the chain ? ". Pro saw will be lovely new and a good chain will last better than cheap one but you've still got to maintain it and sharpen chain, might as well learn on the saw you have.

Nice example there wyk, and that's a 65 cc saw. Presumably that was enough pulls for pressure to reach a maximum. Where's the valve on the Procto, which end of hose ? 200t is half the capacity (near enough), gonna have bigger effect.

You've hit the nail on the head there. Plus where the one way valve is in the tester - if your wee chainsaw engine has to pressurise a length of hose before the valve then you get the wrong answer.

Glad it was as simple as that and you got it sorted. Good result. Please do revisit your compression tester on a few other saws - for your own reference.

If you have a question mark about the compression tester, try it on some other good saws just to get a feel for where the 200T is in comparison. 150psi isn't outstanding, 200T's aren't high from factory either. I was trying to say if fueling is a bit wayward then high compression helps - in the context of fuel preparation. Plus it's a ball ache to pull it apart again to delete base gasket (did you check squish clearance when you reassembled ?) Presumably your new carb is the latest and greatest version of original, Spud or someone with part number experience will know. With the other running issues, ie different engine speeds depending on saw orientation I'd be looking at the metering arm setting in the carb, that can throw up some weird behaviour if it's a bit low. (I'm assuming you've checked there is some play in the throttle linkage and the engine mounts aren't shot etc).

Used to be known as fuel preparation (or lack there of). For decent combustion in a petrol engine the fuel needs to be spread evenly through out the fuel/air mixture in near vaporised form. Carburettors do an approximate job at best - you rely on a bit of the fuel preparation to happen as the gas is drawn into the cylinder, the turbulence and heat help vaporise the fuel. If you think about the low speed or idle circuit in the carb the fuel is drawn through deliberately tiny jets into a turbulent flow of air as the air comes past the butterfly valve. As soon as you open the throttle the fuel comes from the bigger main jet into a less turbulent air flow. I suspect without the engine temperature to help atomise the fuel, preparation is poor enough that combustion struggles. 150 psi isn't that high either, higher compression is more tolerant of poor mixtures. Compression might go up a tad as the engine beds in. If it's only from a cold start (ie doesn't happen after a hot start) I'd say that's what it is. Alternatively could be something to do with the dreaded accelerator jet but on a brand new carb should be OK. Does the new carb have exactly the same part number as the old ? Lastly, if your on old fuel you might have lost some of the more volatile elements of the fuel - just the feature of the fuel you need under cold conditions. HTH. Edit - big fat spark helps with poor combustion issues too.

.... don't know the answer to your questions, didn't see much point commenting.... Think you're going to be very lucky if you find someone who has experience with that saw, doubly lucky if said person knows answer to your question. Homework time ...

Did you clean out the ring grooves with solvent or just check rings moved in grooves ? The fact that the saw ran at all tells us there wasn't a mega amount of friction. If it idles on std carb settings (ie carb idle speed screw not wound in), that says the small amount of combustion energy is enough to overcome the normal engine friction at idle. Any extra friction in the engine is most notable at idle where the combustion energy is tiny. Does it pull over noticably easier now ?

Err ...chain pitch. ... Just because life is what it is and not simple or straight forward there are several pitches of chain. The common ones: 3/8 Low profile, 0.325 and 3/8 std. There are others: 1/4 and 0.404 The pitch is the distance between rivets, measured in inches. So you originally had 3/8" (probably low profile) and you've bought 0.325" bar and chain. The drive socket, bar sprocket (if there is one) and the chain all need to be the same pitch. Typically, one would buy the approprite bar and chain to suit the drive sprocket and save the hassle of swapping sprockets. Also worth considering, a 0.325 chain will be bigger than a 3/8 low profile chain - taller, wider cutting teeth which require more torque and power from the engine. The length of bar is a consideration too but if you are milling you will not be using the full length of the bar so maybe ok in a hobby milling type application. ..but don't expect rapid progress.

Dinosaw - you're quite right that wouldn't work. Material removed from the housing and from the engine pan to get crank back on centreline. Spud - that's how it goes into housing. The plastic bosses for the bolts are a good deal thicker than surrounding plastic. So far so good, done something like a dozen tanks of fuel clearing up a fallen oak. Engine has had a bit of work, could do with a tad more compression (i got that wrong, 24 thou squish) but its not bad for what it is.

Ah-ha, my pictures weren't clear then ! What you see in those pictures goes straight into the housing as is - compete with fasteners. Further set of nuts to clamp the engine into the housing rather than the std bolts. This was a solution I put together after those long bolts came undone in use - big air leak.

Brake band is number 10 and lever to operate it no 11. Brake band would squeeze the clutch drum 12 to stop the drum spinning. I know exactly the noise you're talking about when you refer to a skate board wheel, noise from my youth. Can't help but feel that would get downed out by the engine. Even the blades make a racket. You could take the blades off and run it again - see if you learn something....

Sorry, think I had my head up my backside back there. Clutch bearing is in the housing 1 below the clutch drum, item 3 in picture below ? Ball race bearings usually pretty quiet from new usually get louder with age but hardly, not much being in. I struggle to believe you'd hear a bearing above the engine. It's more likely to be gear whine ... If the old bearing was totally knackered, clutch won't have been running true, might have implications for the gear. Or maybe the brake band rubbing on the outside of the drum ?

Assume the crank is still OK ? The bearing is spinning at idle and up to point the clutch engages in drum. Once engine speed is high enough the bearing is stationary, is that consistent with the nose you hear ? A word of warning, don't run the engine above idle without the clutch drum fitted, otherwise theres nothing to stop the clutch weights from ever expanding.

For a short while, yes. Then it becomes something else. Just like all of them accelerator piston circuits. Aftermarket carbs although hit and miss on quality don't have this feature.