ms261 problem. back firing

[WoodED]

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:

 

when i meet you guys il buy you a pint.... sound

[spudulike]

when i meet you guys il buy you a pint.... sound

 

Sounds like a deal, let us know how it goes, use the Stihl double ended piston stop (not the metal one) or rope to take the nut off and do it up. Nice cheap repair:thumbup:

[Matthew Arnold]

Slight derail but what would cause an MS341 to phut/fart back through the carb creating a little cloud of vapour coming from the air intake when started once warmed up?

[spudulike]

Slight derail but what would cause an MS341 to phut/fart back through the carb creating a little cloud of vapour coming from the air intake when started once warmed up?

 

Is it doing it on idle or when running at speed, what you describe sounds like blowback from the crankcase in to the carb caused by the piston on the downward power stroke forceing fuel vapour back in to the carb - only seen this on an 024 that was running a bit rich.

 

If the 341 is high mileage, then it could be worn piston skirts causing the issue - If the inlet ports have been widened, it is possible the piston skirt isn't sealing the port properly - Oops:thumbdown:

 

A couple of other things to check based on the possibillity of getting strange ignition timing - check the flywheel to coil gap - should be a typical business card thickness and also check for any wear or damage on the HT cable and ignition cut out wires - it is possible it is effecting the spark timing.

 

Bit strange that one - I have known it on fourstrokes where the inlet valve seats are shagged but these are two strokes:confused1:

[WoodED]

once again spud you were spot on.. wipped the nut of the flywell and you could see straight away that the flywheel key had shered of and the flywheel had rotated 30-40 degrese around to the right.

top man

[spudulike]

once again spud you were spot on.. wipped the nut of the flywell and you could see straight away that the flywheel key had shered of and the flywheel had rotated 30-40 degrese around to the right.

top man

 

Glad I could help, just need to get hold of a key and fit it now:thumbup:

[Matthew Arnold]

Is it doing it on idle or when running at speed, what you describe sounds like blowback from the crankcase in to the carb caused by the piston on the downward power stroke forceing fuel vapour back in to the carb - only seen this on an 024 that was running a bit rich.

 

If the 341 is high mileage, then it could be worn piston skirts causing the issue - If the inlet ports have been widened, it is possible the piston skirt isn't sealing the port properly - Oops:thumbdown:

 

A couple of other things to check based on the possibillity of getting strange ignition timing - check the flywheel to coil gap - should be a typical business card thickness and also check for any wear or damage on the HT cable and ignition cut out wires - it is possible it is effecting the spark timing.

 

Bit strange that one - I have known it on fourstrokes where the inlet valve seats are shagged but these are two strokes:confused1:

 

It does it when you pull to start it when it has been running for about 15 minutes flat out. Its about 4 years old and has done for the past 3 months. HT lead and earth leads are all good as just been replaced to try and solve issue. Will check the flywheel coil gap tomorrow morning and let you know the outcome.

[spudulike]

It does it when you pull to start it when it has been running for about 15 minutes flat out. Its about 4 years old and has done for the past 3 months. HT lead and earth leads are all good as just been replaced to try and solve issue. Will check the flywheel coil gap tomorrow morning and let you know the outcome.

 

It may just be a dodgy coil but worth doing the normal checks before trying another coil unless you have two of these saws.

[Matthew Arnold]

It may just be a dodgy coil but worth doing the normal checks before trying another coil unless you have two of these saws.

 

We have two but it is only the older saw (older by a month) that is causing the problems. It occasionally floods easily when started from cold but the compression is good and the piston doesn't look scored.

[spudulike]

We have two but it is only the older saw (older by a month) that is causing the problems. It occasionally floods easily when started from cold but the compression is good and the piston doesn't look scored.

 

The flooding from cold can be linked to a needle valve in the carb not shutting off properly - it can cause fuel to leak in to the crankcase if the saw gets hot from being cold as the tank can pressurise and force fuel past the valve - depends on what sort of breather the saw has - one way or two way flow!