bmp01

I can see the logic in that. Should be the simple start mech but even so could be something that binds when it's under load and doesn't when the plug is out (no load).

Ok. So, what was the reasoning with putting oil in there in the first place?

Just a thought on the hydraulic lock theory suggested here with loil below the piston - if the saw is held completely upside down, the piston will be like a cup holding on to the oil. To get that fluid out, place the saw on its side (either the chain side or the pull start side) and turn the engine over, this should allow the liquid to flow through the transfer ports to the top of the piston. Then you can turn it upside down again and drain from the spark plug or if the exhaust is still off you can drain it from there....

Good result, another one dragged back from the grave ! I have to say that's brilliant service, running saw AND a detailed diagnosis report. Don't see that too often. Did i mention I hate accelerator pumps before now . .... I did ?..... Oh ok, I'll shut up then. ....

It could. ...... but then again it might never, ever ...... run again..... I get the feeling is either goosed or something daft. And before long it will be more economic to just swap the engine (and carb) for some aftermarket parts.

If you read the first post through he says it was hard pull over and that's why he put some thin oil down the plug hole. .... it subsequently loosened up (or he just got used to pulling it over). Maybe the O.P. can confirm that's true AND if the brake was on or off and if the ignition module had been gapped correctly at that stage. Actually just take the 5odding ignition module off, take the clutch off, and show us a picture of the piston through the exhaust port....... bmp01

Micky, It probably would be quicker/easier to get some one to look at it for you. But before you do a couple of quick things to put to bed: -Post a picture of the piston as seen through the exhaust port (now you've got exhaust off). -Really make sure you've got the chain brake disengaged. -Pull the clutch drum off ( its the thing the drive sprocket is joined to, held on with the 'E' clip) and the bearing inside. You need the chain brake disengaged to do this as the brake band will grip the outside of the clutch drum. Do NOT attempt start the saw like this (ignition off please while you pull the cord) we're just trying to find out if the clutch was making the saw hard to turn over. Maybe there will be a clue in here. By the way, not every MS181 has the Stihl easy start mech, but it's a small displacement saw that should pull over pretty easy anyway. bmp01

The thing is the oil filter is more of a rock catcher than a filter. And the stupid flippy cap filler hole - is designed to catch (and trap) saw chips - its pretty difficult to imagine any oil pump having a long happy life. At least on the 170 / 180 you have an oil cap that covers the filler hole.....

Cor blimey, where to start...... What were storage conditions? Warm and dry or cold and damp etc? 1) Saw should not be hard to pull over just because it's been stored. 2) Coil should not go bad just because it's been stored. Have you got any evidence of corrosion on the outside of the engine, rusty steel parts, dusty white deposits on aluminium? Has the clutch rusted up, or is the chain brake on? Can you pull the chain round easily by hand? The oil you put in the cylinder will be causing a really good seal around the piston whereas the (dry) piston ring would allow some gas past. In addition, if there is enough oil in there, you will also increase the compression ratio. That is why it is hard to pull over. I would add some petrol to the brew, pull it over with out the plug in - then turn the whole saw upside down and pull it over. The intention being to empty out all the oil. IF you get it to a state where it pulls over sensibly with the plug in, then you can move on. A squirt of fresh 2 stroke mix down the plug hole, see if it coughs. ....

Yep, that skinny chain cuts a narrow kerf, makes the most of the 170's power - but really fragile. Every thing is fine in clean wood but hit a stone and the teeth fall off. 180 has a few more cc's and little more power. Carbs have idle speed adjustment only. Not had any trouble with oil pumps personally, but known to be weak, block up and wear out at high miles. It is the same pump as the Stihl pole saw. bmp01

If I'm reading that correctly a modified exhaust isn't what you need, or at least not straight away. The first thing your saw needs is some maintenance and a tune up. Either that or the 2 stroke your using isn't fit for purpose, could be an old fuel/oil mix ?? What you've described sounds like your saw is running rich - too much fuel in the air / fuel mixture. Is your saw chucking out blue smoke? Engine maintenance, clean the air filter, new spark plug, general clean and check the carb doesn't have the choke suck on.... Carb tuning has potential to 8ugger your saw if not done correctly, do a search for correct procedure. Exhaust mods, can be as crude as just making bigger holes, drill, files, Dremel. .. that sort of thing. ATB, bmp01

There are always exception to the rule but generally speaking exhausts are not interchangeable. There are plenty of modified exhausts aimed at improving engine performance but mainly these are the original exhaust which is then modified by tuners (or diyer's). 99% of the time the aim is simply to reduce the back pressure on the engine - think bigger exit hole(s). The 1% of the time a tuned pipe is used to create pressure waves to help pack as much fuel and air into the combustion chamber as the exhaust port closes (trouble is the required pipe length is too big to package sensibly for every day use). The benefit of a modified exhaust (or muffler mod in US speak) is dependant on how strangled the exhaust is in the first place and another general rule - older saws were less strangled than modern emission regulated saws. The recent tend has been to make an exhaust with a small exit hole and convoluted path for the gases to travel through - with the intention of reducing the amount of air and unburnt fuel being spilted out the exhaust (during the scavenge stage of the 2 stroke cycle). The attached picture is an exhaust for Stihl MS211 / 181 /171. Original exhaust has an internal passageway plus small exit. The modified one has 2 outlets, my intention was primarily more passageway area. The internal baffling was also removed. Back to back testing confirmed a big performance gain. After the basic stuff like saw maintenance, in particular a sharp chain, the biggest performance gain is usually through exhaust mods. Please note: the carburetor must be retuned to ensure correct fueling after exhaust tuning - otherwise you are likely to seize the engine.

Forest, Was that second new chain similarly affected ? Your dealer ought to hear about this and if he's got any lead in his pencil he ought to get onto Oregon swiftish. I'm not going to say too much but the implications of running that setup are not good - we have a responsibility to do something about it. bmp01

Chain is assembled from a long length of chain, cut to length and a joining link used to complete the loop. Operator is making up X quantity of chains of the same length and the bag of joining links he uses are the wrong ones. If the chains are coming direct from Oregon then that's pi55 poor quality control. I bet it's not Oregon though. Be interesting to see what packaging the chains came in.

Can you imagine the responsibility in the shop in tracing a batch of chains that are all wrong. I could easily see some engine damage from running such a setup.

Just go and put a pen mark on the chain where its clicking, wind it round and round. I can pretty match guarantee its going to be that link every time.

But if all the chains are coming from the same place. .. are they all wrong???

Come on guys, there's a link in that chain with the wrong pitch

Well, isn't the evidence right there in your picture? That drive link is different to its neighbours. .... looks like an assembly link to join the chain loop. Is it this link every time the chain goes round? Edit : Even the distance between rivets looks different.

Your carb looks straight forward, fuel in past the metering valve, fuel into engine via the single brass insert jet and fuel to primer via drilling and brass pipe. Are there any other drillings or jets coming off of the metering chamber? If not then doing the suck and blow test through the brass insert (WITH both the adjuster screws fitted and adjusted to 1 turn out) should tell you if the one way valves are working. I would repeat after feeding some WD40 into the same brass insert - sometimes that can "wake up" the valve. Blowing through the adjustment screw holes doesn't tell you anything..... A carb rebuild is usually limited to replacing the diaphragms, the little gauze filter and the metering valve / metering arm. You can replace the little aluminium plugs but it's only necessary if the passageways below are blocked and you need to gain access to clean them. So, normally it's take carb apart, clean, reassemble with new bits. ...not too hard. So anyway, you did check the diaphragms for holes ??? bmp01

Good observations. So was the metering chamber full of fuel or not? Take the pump side apart too. Fuel or not? Is the pumping diaphragm intact? IF the pump side is good, AND the metering diaphragm is sound, then the only way the air is being drawn into the fuel is through the jets in the carb. ....normally in the running engine the're flowing fuel into the engine, it's only the one way valves that stop the purge system from drawing air backwards through the jets. ....

You'd struggle to start the engine in that case. ..... the man says "it bogs" so presumably it does run when hot just badly. Deano, Wind the low speed mixture screw out a 1/8 turn then another 1/8 turn. ... Oh you've done that already? Can the engine be persuaded to higher speed when hot, if you accelerate it gently? If it were only the one carb I'd say damned accelerator pump (in the carb) but tried two carbs so I'd say damned accelerator pumps Unless one or both carbs have been tested on another saw and proven to be good, I'd say they are still suspect. Good luck, make sure you find why it seized in the first place or is going to happen again.

Ah, but did he? You're probably right but i wanted to confirm the fuel in the pipe was getting all the way to the primer and not just shuffling back and forth - seems pedantic maybe but sometimes it's not 100% certain which way fuel is flowing when it's pulsed with a primer. .... or maybe that's just me

I should have paid better attention to your original post. .. so it's been apart already . Two questions, 1) Are you seeing fuel in the primer bulb? If so, that should have filled the metering chamber with fuel.... and it should then at least cough on 2-3 pulls. If no fuel in the primer bulb then, did you get the fuel lines swapped over? Or the filter is completely blocked or the metering valve isn't opening (metering gasket upside down? Check metering lever setting). 2) Is the choke mechanism operating as it should? You need it to create the vacuum to suck the fuel in. .. If you do take the carb apart again, confirm all jets etc are unblocked with something like WD40 spray through one of those thin tubes. DON'T use compressed air at full pressure that will knacker the one way valves (one in each of the low and high speed circuits). I've got a short length of silicon hose which is very soft and can be pressed onto the entry to the drillings and sealed by hand pressure - blowing (and sucking) confirms drillings are clear and one way valves are working .... (or not). Doesn't taste the best but you learn a lot At some stage it might be worth popping some fuel down the spark plug hole, just to confirm the engine will run once the fueling is sorted.... Let us know how you get on. bmp01 -

Nope .... but if you are lucky you might avoid getting some of the surrounding crap down the holes If you're unlucky things are going to take a turn for the worse You could wind the screws in gently, then back out 1 turn each (typical factory setting) but don't hold out too much hope. ... Most likely the carbs going to need a going through, inspect and clean plus maybe new gaskets. You should also check the rest of the fuel hoses, filter etc. Thing is, if you can't get fuel to the saw with the choke on, then some thing is blocked or stuck - your not reliant on the pumping side of the carb under this mode of operation. bmp01