Stihl electronic ignition unit failures

[blazer]

A while ago I posted a problem with a MS280 ignition problem and later a starting problem with a FS100 which again turned out to be the electronic ignition unit. Measuring both units with a DVM on the LT side they both gave a reading of +2M ohms both ways, whereas the new units gave a reading of say +6Kohms, so any unit that give a 2 meg ohm reading is faulty. Both units are 10 yrs old with light'ish use, I'm not moaning about Stihl products but it may help with anybody with a simular fault to check the low tension side of the ignition units, both units are slightly different so I couldn't swop to test.

 

The symptoms were simular the MS280 kept cutting out or would run for a while then cut, suggesting a blocked carb but then it ran for 30 sec and died - no spark. The brushcutter was a sod to start but ran ok but still had a weak spark, so again I thought it was a carb problem.

 

Both units are now starting first time and running well:thumbup1:

[gensetsteve]

If you allow the engine to tick over for a minute or so after heavy work I have a theory it helps extend the life of the coils. Shutting a hard worked 2 stroke down leaves alot of heat which travels up the crank to the flywheel. I would also think leaving an engine to tick over allows a better coating of oil for the bearings on restart. When i start my saws I tend to allow them to idle on the ground for a while then pick a small log and use 3/4 throttle. Just feels a bit cruel on a frosty morning to plough into a 2ft but 10 seconds after starting.

[Mesterh]

If you allow the engine to tick over for a minute or so after heavy work I have a theory it helps extend the life of the coils. Shutting a hard worked 2 stroke down leaves alot of heat which travels up the crank to the flywheel. I would also think leaving an engine to tick over allows a better coating of oil for the bearings on restart. When i start my saws I tend to allow them to idle on the ground for a while then pick a small log and use 3/4 throttle. Just feels a bit cruel on a frosty morning to plough into a 2ft but 10 seconds after starting.

 

 

Isnt that bad for the engine though?

 

I always thought that 2 strokes dont like to be left on tickover as it starves them of oil.

 

Plus I would imagine that its even worse these days as they run so lean for emission control etc.

[gensetsteve]

Isnt that bad for the engine though?

 

I always thought that 2 strokes dont like to be left on tickover as it starves them of oil.

 

Plus I would imagine that its even worse these days as they run so lean for emission control etc.

 

It could be, my thing is big diesels and it could be because we cancel the load for a few minutes to save the turbo before shut down. Maybe someone like spud could advise. I would have thought any oil round the bearings is more likely to evaporate if the saw is cooking with no air flow. You could be right especially with the new saws.

[Megatron]

A saw is tuned/jetted mainly for operation at idle and full throttle. Letting a saw warm up on idle should be fine, in cold weather if you don't warm a saw up you can cold seize it. The piston heats up and expands faster than the cylinder. Warming a saw up on part throttle is not a good idea in my opinion as depending on the model carb and the exact throttle plate angle, this can cause the saw to run lean.

 

I am aware that "modern" saws are tuned leaner (at idle and full throttle) but it should still idle without starving the saw of fuel and oil. If you are milling a long hardwood log it is common place in my experience to stop periodically to allow the saw to return to idle and cool.

 

As a general rule the ignitions on chainsaws don't like heat! Keep the holes in the recoil housing, the flywheel fins and around the ignition module free from crud. (and the cylinder fins, to keep the cylinder cool)

[Mesterh]

A saw is tuned/jetted mainly for operation at idle and full throttle. Letting a saw warm up on idle should be fine, in cold weather if you don't warm a saw up you can cold seize it. The piston heats up and expands faster than the cylinder. Warming a saw up on part throttle is not a good idea in my opinion as depending on the model carb and the exact throttle plate angle, this can cause the saw to run lean.

 

I am aware that "modern" saws are tuned leaner (at idle and full throttle) but it should still idle without starving the saw of fuel and oil. If you are milling a long hardwood log it is common place in my experience to stop periodically to allow the saw to return to idle and cool.

 

As a general rule the ignitions on chainsaws don't like heat! Keep the holes in the recoil housing, the flywheel fins and around the ignition module free from crud. (and the cylinder fins, to keep the cylinder cool)

 

Cheers for the info.