bmp01

Ok, that's it then, sorted. Quicker and easier to do - than to explain it ..... again.

Pretty straight forward..... takes me back to the days of setting the timing by rotating the distributor back and forth. .. remember them ??? Back to the present, that strobe test would be worth while. But you need to know what the spark advance should be in the first place before you can draw any conclusion.

Yeah you're right, my comment was incorrect, my intention was to keep away from max rpm while checking the coil (to avoid any misleading behaviour) which is still the right approach I think. Worth noting: In and out of 4 stroking due to fuel mixture does cause engine speed to oscillate somewhat but with an electronic tach which averages several revolutions you get a sensible speed reading. Compare that with an rpm limited coil dishing out spark cuts, counting sparks with electronic tach to determine rpm just don't work. (Ironically though, the engine speed is precisely controlled by the electronics at that stage and the mechanical bits are seeing a constant rpm ). Spud - any idea if the 024 coil has an advance curve in it or fixed timing?

Sorry to hear some bu88er has messed up your happy setup. Regarding the 181 its not a high torque saw, generally needs to be kept spinning fast and not loaded up - so don't push on it. The wider chain is what it is - you will be removing more wood with each cut compared to the micro chain and need more torque to do so. I've always been pleasantly surprised how well those thin chains cut but the down side is they are very fragile. Even though you are used to the low power 170, try the 181 with attention to a light cut aiming to keep the speed up. And keep a good eye on a sharp chain. Give it 3 or 4 tanks worth to loosen up.

You might get some weird numbers at max rpm even without a limiting coil - if the saw is 4 stroking the real rpm will be all over the place anyway. But upto 10000 (let's say) rpm should be pretty stable. With the age of saw it's quite possible the spark plug lead is past its best too. Expect you can you change the lead by itself on this coil. Thing is, from your video sound track it didn't sound like there were misfires during the cut, just low power.... What about spark advance - i don't know if these coils have an advance curve built in or fixed timing but a retarded spark would considerably reduce power. Same would happen if the flywheel has lost its timing or been messed with.

They don't sound hugely different in terms of how they react to load.... play back through any computer isn't going to be ideal and can't tell what load you are applying. But here's what i thought. -Neither saw seemed very responsive, they don't rev up crispy. -Sounded to me like the second saw (251) was a bit low on revs and quite a heavy 4 stroking out of the cut. (I know you're not questioning this one, but to me that's not where it should be). -Yes, the 240 is a lower engine speed still and struggling. Have you considered bar and chain differences, is it worth a chain and bar swap between the two? How you have set the raker heights on the chain(s)? Its as if the rakers are too low. But then if the engine is gutless i guess its going to behave like that. Probably a red herring but worth an ask. Did you get the compression test done? Unlikely to be any silver bullets here, going by Spuds opinion but it don't do any harm to consider a few alternatives Also, didn't you say the saws behaviour was essentially the same when it was on Stihl pot and piston ?

So, how it works. .. Under choke conditions the choke blocks the inlet track (duh !) which causes a big depression in the carb port AND in the metering chamber (via the tiny jet holes). It's a much stronger depression with choke compared to normal running condition. It's the depression that sucks the metering gasket down onto the metering arm thereby opening the metering valve. Quite simply the bigger the depression the further the valve opens. If you are marginal on opening the metering valve you can see the height of the metering arm or the size of the 'pip' on the gasket are important. If the metering gasket is up side down. ... there's no 'pip' on gasket, so need big depression to get any movement of the meterIng arm and valve. HTH.

+1 Having the metering chamber gasket the wrong way up does exactly what you experienced. ...runs on choke, runs on fast idle then dies, repeat as often you like. Don't ask me how i know this. If the metering arm height is set too low it could do exactly the same. Just saying .......

That's a whole lot of ally swarf and big chunks to collect on the piston must happened pretty quick, a few seconds only, maybe as saw slowed down. It's piston crown is cracked through. ...? I'm not sure if i can see a cracked piston there or not. Would that be primary or secondary failure? Crankcase is brown, piston is same colour above and below the ring so I'd guess combustion gases below the piston. Edit: but the ring is stuck so that might be a red herring. .. Don't know what that other 'stuff' is on the piston, looks like chewed up green plastic, bearing cage? Is there any ally below the piston - can't see any, but blurry though. Good puzzle, another clue please....

Thanks for replies, balanced opinions based on usage I'm guessing. Right then, had a chance to give the saw a once over. It's actually 2002 model, nearly complete, missing an AV mount under the exhaust. 25" Bar and chain, chain has had it, needs a new rim sproket too, otherwise and cosmetically pretty good. Unfortunately, the compression tester says, 135 psi (125 to start, with decomp button in). What i can see of the cylinder through the spark plug hole (exhaust side) looks nice and shiny. The plug was well carboned up. Running at idle, it rattles just a little bit, not imminent death but just enough to make you wonder. Is this typical? Blips nice and revs out fine. I guess if it's a genuine healthy cylinder and needs either a set of rings or a piston that's ok - are there any external casting marks to identify the cylinder? Thanks, bmp01

Jeez, really ? We better not think about the cost to get to a dealer to collect Aspen then ....... or the time wasted waited for a delivery. Don't get me wrong, i think Aspen is a good product but it needs to be sold on its merits.

Spud, Thanks for that, rather encouraging. Fingers crossed then. I'll check the compression and pop the exhaust off - just to be sure.

Hello, I'm out of my depth here - are there any model specific weak points on a Husky 395XP, 2004 vintage ? I'm told the saw runs fine, idles ok has decent compression etc pictures show the plastics are decent. Are there any weaknesses in the chain drive, oil pumps, chain brake ? Or anything else critical / expensive that wears or fails? Thank you.

Was the cylinder and piston assy a genuine part - the one that failed? Not often you see that. .... After market circlips and rings on the other hand are less reliable, some builders substitute these parts with genuine ones. Personally i don't like circlips with those extra "grab here" features on them - the extra wire mass is subject to the same accelerations as the rest on the piston and that means there more likely to move / fret / break.

No fuel through the low speed circuit in the carb? Has the 'new' carb been proven work properly? Do you manage to the saw start with the choke enabled? Will it then run briefly at low speed or not at all ? bmp01

I would be tempted to pressure test the saw before you pull it apart, nothing to lose and maybe learn something useful.

All aftermarket pistons are cheap really, even decent Meteor brand. Time and effort to clean up a genuine cylinder etc, 10 pound cheapie or a 25 pound Meteor piston....... I don't feel the need to experiment with cheap

As per previous comments, if you don't fix the route cause its going to happen again. It would seem you never quite got the saw fixed in the first round of repairs so you'll be looking to dig a bit deeper this time. Air leak is favourite, so make sure you pressure test the repaired saw or get someone to do it. Only useful thing to add, if the original cylinder isn't trashed too bad it can probably be brought back to life by removing the aluminium deposits. Takes time but if you end up with a good, genuine used cylinder I'd take that over a replacement one. ... do a bit of research on here for 'how to....' It's a good saw, worth the effort.

Going through a rather tired MS171 which came to me as a box of bits, nothing very exciting. Reason for posting - noisy crank bearing led me to remove and disassemble the bearing, idle curiosity. Picture is worth a look. Look at the ball sat on the blutak - the outer layer has disintegrated. Poor quality steel I imagine. Bearing is Chinese, with C4 clearance, i thought these were C3 clearance so might be an aftermarket item ? bmp01

Jeez, that's some oil slick Yeah, I can sort of see the problem, exit in the exhaust is quite high up, higher than the exhaust port. And there's a stupidly small internal passageway inside the exhaust that would stop the oil draining even when you tip the saw forward. Ho-hum. Easy in hind sight innit... So, how big was that mysterious blue cloud over Heanor today then ?

Nice one Micky, good result. As to your question, took the plug out and span it over with a drill ......

Did you get much oil out of it? Put the clutch drum back on (if you haven't already) before firing it up.

Piston's Peachy. No problems there. Strange exhaust port though, bit difficult to make out the shape, not seen one like that before. .... Is it a genuine cylinder I wonder ? bmp01

Ok, thanks for clarification. ... seems i misunderstood, got the wrong end of the stick, etc, etc. As others pointed out, if it turns easily with the plug out, there is no need to be looking at clutches, chain brake, ignition coil foulIng the flywheel - my mistake, apologies. Still worth posting a picture of the piston seen through the exhaust, or at least confirm the piston is good. You should see the faint machining lines running around the bottom half of the piston, so below the piston ring. Any vertical lines are damage. There's a thread here just recently "Does this cylinder need replacing" with some good pictures in it. So have you managed to get any gunk (oil) out of the saw ? Keep us posted. I'm close to Jn 16 on the M1, bit of a trek but happy to help ... bmp01

And 3 pounds of that was for the accelerator pump parts