Stihl MS261 mtronic

[spudulike]

3 hours ago, Muddy42 said:

Where are you? Someone nearby might lend you a mityvac. If you still can't tell where the leak is coming from with the mityvac, no leak can hide from a dunking in a bucket of water.

 

I've often wondered if you could make a basic pressure tester with a bicycle pump.

Yes, that was my first pressure test rig.

[pleasant]

use the carb spray or brake cleaner trick. Get it started and if you can get it to a set speed on idle, then using one of those thin long tubes on your spray can gently spray around the machine in areas, such as the flywheel, clutch area, manifold...avoid anywhere near the air intake though. If you have an air leak the revs will increase from where you have it set as it will scavenge the carb spray and will richen you fuel.

 

it's a start if you haven't got leak down equipment

 

 

[BlueMax]

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.

[BlueMax]

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

[BlueMax]

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?

[BlueMax]

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?

[Dan Maynard]

Top tip, the clutch is a left hand thread.

 

Good that you're homing in on the problem. I think have the cylinder off next, check out the piston and cylinder as may have been FUBARd by the air leak, or may be ok.

 

If it needs piston and cylinder then work out price and how keen you still are to carry on before doing anything else. On the other hand could be the cylinder cleans up and a new piston not too expensive so still viable.

 

Cylinder off, imo.

[adw]

Your very brave running that saw with no drum and clip on, the clutch is spun onto the crank and can and will spin off on the over run destroying everything in its path.

[spudulike]

13 minutes ago, adw said:

Your very brave running that saw with no drum and clip on, the clutch is spun onto the crank and can and will spin off on the over run destroying everything in its path.

And the clutch could open up taking out the brake band and anything else in its path!

Should have removed the clutch then done the test.

[BlueMax]

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.