What's on your bench today?

[GardenKit]

Been working on two more MS200s -full refurbs plus a 357XP that needed a new cylinder, fortunately had a scrapper with a good cylinder. All is now good and all are running well.

 

Had a KM55 in with a bad coil - tried aftermarket but it is backfiring like it has been on beans for a week:blushing: Checked the flywheel key and that is fine so all I can put it down to is the coil isnt right.

 

I have noticed that most coils line up with the flywheel magnets at around TDC or circa 25deg before TDC, This unit has this happening well after tdc so expect the aftermarket coil is triggering after TDC causing the backfiring issue.

 

Now have an OEM coil on order and hopefully this will sort the issue!

Those Stihl coils have always been rubbish Steve. As Wisco says, they have superseded them several times and they are still rubbish.

 

It seems that Stihl can never fix anything properly.

 

And you backfiring is indeed the result of using the wrong coil for the flywheel.

[spudulike]

Those Stihl coils have always been rubbish Steve. As Wisco says, they have superseded them several times and they are still rubbish.

 

It seems that Stihl can never fix anything properly.

 

And you backfiring is indeed the result of using the wrong coil for the flywheel.

 

From the design of the engine it looks like the coil and flywheel magnets align after TDC so the spark must be timed at around 300 degrees after this point. The aftermarket coil triggers immediately so is sparking on the downward stroke hence the backfire.

 

I have a secondhand 4140 1303A on order and this coil is used and now superceeded by 4140 1308 on models after 2001. My unit conveniently has a big scratch through the date but looks to be 2006. The aftermarket coil has 1308 on it but reckon it isnt as it hasn't got this strange delaged spark that the OEM part must have - fortunately only cost £12 but still annoying!

[GardenKit]

Pretty sure from memory that the flywheels changed at the same time as the coils.

 

Will check in the morning.

[bobh]

I'm sure this has been covered before somewhere way back in this thread but is there a way of testing coils?

[spudulike]

I'm sure this has been covered before somewhere way back in this thread but is there a way of testing coils?

 

Stick your tongue up the plug cap and spin over the engine, if it throws you across the workshop, all is OK:lol:

 

I just put them on the engine, plug up the cap, earth the plug on the cylinder and pull it over. It should spark.

 

I usually measure the continuity between the plug cap and the kill contact just to make sure the HT lead and spur connection are OK but it doesn't ensure the electronics and the rest of the coil are OK.

[GardenKit]

Stick your tongue up the plug cap and spin over the engine, if it throws you across the workshop, all is OK:lol:

 

 

I know spud is normally right, but this time I have to argue:sneaky2:

 

Do not try this at home kids, unless you have a paramedic to hand.

[bobh]

It'th two late

[bobh]

Forgot PIC

[GardenKit]

Thats what you get for sticking your tongue where you should not Bob

[div_h]

It'th two late

 

Never tried it but my tradesman said years back, if you grabbed someone's hand then touch an HT lead (on a car) they would take belt and not you? I've had a few moments touching HT leads 😜