ms261 problem. back firing

[WoodED]

was a wet morning yesterday so we stayed in the yard (nice and dry with a kettle on tap ) and did some tool maintanece.

 

my collueges work saw is a ms261 and he took the clutch of too clean out behind it checked the spark plug and them reasembled it. he then tried to run it up afterwards. the saw was warm so didnt need chocking. after about the third pull it just back fires with quite a loud bag. another four pulls and the same thing happens. then chocked it and it doesnt fire but back fires again.

 

the plug looks fine so what could be wrong with it? any ideas.. i am usualy pritty good with problem anaylsis but i am stumbbled by this one.

 

(and no husky jokes ive already given them to him )

[spudulike]

The most common reason for backfiring is a hot curry and too much Cobra larger on a Friday night, the cure is to eat tofu and humus:lol:

 

Back firing generally screams that the flywheel key has been sheared or the flywheel has come loose and moved. I have had a couple like this and it sared the bejesus out of me until I found it.

 

Other possible issues could be a faulty ignition coil sparking incorrectlyor arking HT lead.

 

It would usually mean that you are getting fuel vapour in the muffler and this is getting ignited by a retarded spark (after TDC rather then circa 6 deg before).

 

My first check would be the flywheel key but anything that could cause intermittent spark or a retarded ignition timing is suspect.

 

Good luck - it's a Stihl......go buy a Husky:blushing:

[WoodED]

The most common reason for backfiring is a hot curry and too much Cobra larger on a Friday night, the cure is to eat tofu and humus:lol:

 

Back firing generally screams that the flywheel key has been sheared or the flywheel has come loose and moved. I have had a couple like this and it sared the bejesus out of me until I found it.

 

Other possible issues could be a faulty ignition coil sparking incorrectlyor arking HT lead.

 

It would usually mean that you are getting fuel vapour in the muffler and this is getting ignited by a retarded spark (after TDC rather then circa 6 deg before).

 

My first check would be the flywheel key but anything that could cause intermittent spark or a retarded ignition timing is suspect.

 

Good luck - it's a Stihl......go buy a Husky

 

spud you no i only buy huskys lol.

 

and call me silly but what is the flywheel key?

 

cheers spud,, top guy as usual.

[spudulike]

spud you no i only buy huskys lol.

 

and call me silly but what is the flywheel key?

 

cheers spud,, top guy as usual.

 

The flywheel - the aluminium disk behind the recoil cover has to be held in a position on the crank shaft to ensure the coil sparks at the optimum time - this is refered to as ignition timing.

 

 

The way this is done is to key the flywheel on to the crank shaft with a steel key - in engineering terms - a "woodruff key".

 

The picture below shows a broken key!

[spudulike]

Oh, I forgot.....you are silly:lol:

[Ricbob]

Spud may be on to something there, did he take the flywheel off to clean?

 

when i have done so i found my flywheel had two positions for the woodruff key, my saw just backfired away to itself until i changed the position and it started first time. i know know some flywheels have different positions for different types of ignition coils and electronic.

 

ric

[WoodED]

Spud may be on to something there, did he take the flywheel off to clean?

 

when i have done so i found my flywheel had two positions for the woodruff key, my saw just backfired away to itself until i changed the position and it started first time. i know know some flywheels have different positions for different types of ignition coils and electronic.

 

ric

 

no but he normaly jams the flywheel with a towel or somthing like that to shock the clutch of with the air guy so i think spuds got it spot on.. il have a look on monday

[spudulike]

Spud may be on to something there, did he take the flywheel off to clean?

 

when i have done so i found my flywheel had two positions for the woodruff key, my saw just backfired away to itself until i changed the position and it started first time. i know know some flywheels have different positions for different types of ignition coils and electronic.

 

ric

 

I'm wondering if he used the flywheel nut to lock the crank to get the clutch off and did the key in. My picture comes from an 028 that wouldn't start but would back fire very loudly, after pulling it over a few times and scaring me, I got to the route cause and fixed it!

[WoodED]

I'm wondering if he used the flywheel nut to lock the crank to get the clutch off and did the key in. My picture comes from an 028 that wouldn't start but would back fire very loudly, after pulling it over a few times and scaring me, I got to the route cause and fixed it!

 

bingo.. like i said he holds the flywheel with a thick jumper or a towel to air gun the clutch off

[spudulike]

bingo.. like i said he holds the flywheel with a thick jumper or a towel to air gun the clutch off

 

Oh dear

 

Looks like I know what I am talking about, one day I will get some beer out of you guys:lol:

 

Excluding Burrell - he is doing some machining for me - cheers Martin:thumbup: