BlueMax

An update, thanks for all the help and suggestions. The machine is now stripped completely. Turns out than the worm gear for the oiler was frozen solid. Possibly the mating gear that rotates with the clutch was stripped, as it’s completely smooth and has no teeth to rotate the worm .The bearing behind it was all shot, it actually was missing at least one ball and the plastic ball spacers and the seal were non existent. no wonder it did not run well or idle, it’s like having a swine carb to suck air through! Difficult to tell which caused what to fail first, the frozen oil pump or the busted bearing. The oils tank had a lot of crap inside as well-possibly old oil was used at some point rather than chain oil. the crank appears to be fine, as I think the lack of a ball or two was making it run eccentrically, as shown by a bit of wear in the inner race of the case.the pistons, rings and cylinder all appear visually fine with no obvious signs of wear. Now I face a rebuild and should be good as new. Thanks for your help. ( and by the way tying 3 knots in a small bit of cord and inserting via the plug hole to use as a piston stop is a brilliant hack!)

Thanks for the tips, and yes I knew I should have whipped off the clutch, could have opened out at high speed. But just wanted to do a quick check and knew not to rev!! Starts on choke and died instantly with the cleaner.

So a question, now it looks like complete strip and replace bearings. Assuming nothing evil with crank/piston. Do I just need the 0322 +1560 seal and and the 4262 +1600 seal. Is the 007 1000 gasket set worth it or just the cyclinder and crankcase gaskets if the others are ok? Anything else worth doing at same time?

I think, I found the issue👍but not so good news. Video attached .I tried the steps in the video posted by ‘pleasant’ and sure enough once it started a quick spray of brake cleaner near the clutch/ oil pump and it instantly dies, tried it three times( with old ignition unit )and same result. So back to store for a refund(maybe) as that was expensive and now how to sort a bearing air leak. I feel like I might be making progress. Thanks for posting the video 👍 any tips on pulling the clutch and replacing bearings etc? IMG_1570.mov

Can’t get I to fire at all now 🙁What I have found is that the clutch side is very oily, see picture, is this normal? I am now wondering if I do have some of bearing seal leak. It’s not wobbling but definitely more oil that ideal, this was after a surface wipe! if I can get it running was going to try the brake cleaner test as I have some

I am pretty sure it’s not an air leak, but will double check especially the decomp. With the plug removed the pressure on the ‘thumb’ is quite strong and I can defiantly tell the difference pulling it over with the decomp in and out. I cleaned and made sure the carb to cylinder block rubber mount was clean and bolted tight with no deterioration in the seal, I then cleaned and made sure the carb to rubber throat was clean and tight( I opened out the plastic holes a bit in the air filter mount to fit my socket easier) to ensure I could make sure the two nuts carb mounting nuts were tight, including the odd shaped metal washer/seal. I am wondering if the main/idle jets are still partially blocked? When I stripped the carb I could blow through the two jet holes at the end of the solenoid gallery with my airbrush compressors(50psi) but the flow was not great, how restrictive are the jets? Seems to me that if it idles great on choke for an entire tank if needed then it has more vacuum to suck fuel and at WOT it has more vacuum so it could be too little fuel flow at idle( or too much air due to a leak), does the electronic solenoid do much at idle to control fuel? All the parts are genuine and match the stihl part numbers for MA261 as far as I can see. I guess next step is a replacement carb, but as I have replaced the diaphragms and solenoid and loom seems a waste.

I will ask, but pretty sure bought from new. My son is a trainee for a sole trader Tree surgeon, and this is one of his saws, he only ever uses Stihl and buys genuine spares. I think it was bought new, used a fair bit then started to be unreliable when climbing. He is not mechanical at all, and possibly did not maintain it well, and so just left it. I volunteered to help ( free labour, I am a bit of an engineer and I spent many years fiddling with model 2 stroke engines in my youth) to try to resurrect it as they need another saw and can’t afford to buy a new one as he just had to have his Kubota chipper engine rebuilt. As you can see I started with the service items, cleaned lots of wood dust out, then did the filters and plug, no joy, then solenoid, no joy, then carb diaphragms, no joy, etc. I havw checked all the bolts are tight for the carb and throat. I can’t tell if it’s making power as I have removed bar for safety while I fiddle. I don’t have the tools to check compression and vacuum so am I at the end of the road for home fixing?

So, the latest. I tore down the carb again, made sure it was squeaky clean, checked the jets where the solonoid site by blowing air form a compressor through. I checked the impulse path all the way through the carb mount and it’s clear. I have bought a new wiring loom form solenoid, and also a brand new genuine ignition module. None of this has made any difference!!! I have tried both reset procedures, I don’t think it’s the new method as if yiu let it idle for 30+ seconds then WOT is stays WOT without any change in revs, so I tried the first method. I am really stumped. It will run on choke and WOT but nothing in between. It will not idle or start without choke even when warm. I am now completely out of ideas as to what to try next. It’s now had a new ignition, solenoid, loom, carb diaphragm set, carb gauze filter clean, fuel and air filter and plug cleaned and set. I have spent a lot to date and achieved nothing, What do I try next?

So the latest. I tore down the carb, removed the gauze filter and cleaned, removed the fuel pin and tiny spring and cleaned, flooded the main body with carb cleaner in every hole I could find. Rebuilt the carb with a new membrane kit (both sides) as the old one looked a bit worn. So I have a new air filter, plug is clean and gap correct, new white solenoid, set gap on control unit to business card width. New fuel filter. Clean fuel. it starts easy on choke now and run smooth…I tried the reset approach, I have the early mtronic so run for 90 seconds on choke and switch off. But as soon as I knock the choke off it dies, it simply will not run on idle at all. I can run it WOT and it screams but as I ease off to starts to chug/bog at half throttle and then dies below that. I am now stumped. Any ideas welcome.

Yup😬…and I bet if I buy a new carb I will afterwards discover a previously unknown break in the solonoid wire or something! Pretty sure it’s fuel starvation at idle.

I have removed the bar for safety to work on it. So the latest is that it start quite easily on choke and will run forever. If I grab the throttle and hold it WOT, with choke off, it will scream for as long as I hold the throttle WO. I can reduce the revs slowly to about half and it’s ok but then as I slowly reduce revs more it start to sound a bit rough and if I go to idle it stalls.if I go from choke straight to idle it stalls. It feels like it might be starved of fuel at idle. If it had an idle jet I would rich it up, but it doesn’t so can’t. As the solenoid is new could the mtronic chip be duff? Fuel is fresh and 50:1.

MS 261 stalls when taken off choke. Spark plug checked and clean, new white solenoid kit installed with new fuel filter. New air filter. Carb taken off and soaked in carb cleaner overnight. instructions followed for resetting by idling for 90 seconds and then shut down. Starts fine and runs on choke but as soon as choke removed it stalls. With cover removed and air filter removed I can see that if I slowly release the choke it’s ok until about half way and then just stalls. Can be run at full throttle sometimes, without choke, but as soon as throttle down it stalls. This is frustrating me, any ideas what could be causing this as a new ignition pack is a costly way to check.