Stihl ms361 surging under full load?

[Neilshep]

Hello

 

I've got this recent issue with my ms361.

 

She starts fine, idles reasonably well has some chain creap that I need to adjust.

 

However my big issue is, under full load she surges revs.. up and down up and down every 3 or 4 seconds.

 

Feels like she's got plenty of power as per normal.

 

I haven't played with the carbs, never had to in my ownership.

 

Any ideas would be appreciated that I could try before I send it to a shop to look at?

 

Many thanks

 

Neil

[billpierce]

Does it surge up in revs or seen to big down a bit at full revs?

[spudulike]

Sounds like the carb is having trouble delivering fuel at high speed or perhaps the clutch is shot. Can't really tell from the description but the fuel issue is more likely.

[Neilshep]

Would adjusting the carb sort this issue out, or is it more lightly it needs a rebuild of the carb? 

 

Thanks 

[spudulike]

It may sort it or just mask the real issue that may cause further damage. If the saw has been running fine for years and is now surging or pulsing something has changed and you now need to find out what. Have you cleaned the breather under the cover where the top handle joins to the side of the saw?

[billpierce]

I've has flakes of fuel line in my carb gauze before which made the saw scream sporadically.

I'd strip the carb, clean it and pop a carb kit in while your at it. Tune up afters.

Have you tried using the saw in different orientations? Does this make a difference to tick over speed?

[Neilshep]

I've checked the breather spud, all looks nice and clean in there.

 

I've ordered a new fuel filter and pipe, going to throw them on when they arrive and then if no improvement I'll move onto the carb.

 

Thank you for the suggestions

[Echo]

Go through the fuel lines and filters, replace if suspect, clean carb well

and put a kit in it, this alone may solve your issue, also ensure there is no

air leak between the carb and the cylinder intake, a leak there will cause your

saw to run lean, rev up and down a little, and it will most likely be there at

idle too, which you seem to say is the case, check or change the impulse line too.

If you can look in the exhaust port to ensure no scoring has taken place on 

the piston, cylinder walls or rings, for any such damage would need sorted

first, I say this because you say the saw surges and seems to have plenty of

power, which can be the case when its running lean, heard it so many times,

saw was perfect, never run better, then no time later the obvious happens,

ceases up because it was running lean.

Hopefully it will be something simple, and as others mentioned, don't run it until

you find the problem, or you could end up going from a cheap repair to a very costly

one, or worse, I think air leak somewhere, if the saw is good enough to be spending money on, then at least change all fuel lines, filter, clean carb and put a kit in it, and check to ensure there is no leaks between the carb and the cylinder, spray some wd40 around that joint or boot, ensure you use the long straw to do this and do not let the wd40 get into the airy breather as that will change the saws sound too, for obvious reasons,

spray it around the base of the cylinder too, while the saw is running of course, and listen for changes in engine tone, or even look out for air bubbles around the case or seals if you have enough panels off to get in at

these areas. It could be simple, and I hope it is.

 

Edited February 7, 2019 by Echo

[Neilshep]

Just a quick update,

 

I changed the fuel line and filter, also rebuilt the carb with a slight improvement.

 

Then I thought, I better get the crankcase seals checked by the shop.

 

Turns out there ok, he gave the saw a service and adjusted the carb.. he did note the ignition module gap was well out? . . So fixed that too.

 

Anyway,  now she's running like new again.

 

Thanks for all your help and suggestions.