diagnose this one!

[NWCS]

customer brought me a saw in that he said lost all the power after about 8 min of cutting on his last job. compression still good. customer has a habbit of letting air filters clog till the saw wont run anymore.. i think he got about 6 hours out of this plug.

 

[havvey]

saw

i would pull the jug or bore scope it don't like the looks of that :yoyo:

 

[ccicora]

What is he running for fuel?

 

[retoocs555]

customer brought me a saw in that he said lost all the power after about 8 min of cutting on his last job. compression still good. customer has a habbit of letting air filters clog till the saw wont run anymore.. i think he got about 6 hours out of this plug.

6 Hours???

 

[NWCS]

customer is running 40:1 Maxima Castor 927. bore and piston are still ok.. i just have to get him to clean his filters now. timing was a little too advanced on the saw also.

 

[ozflea]

I wonder where all the little bits of molten metal that belonged to the plug tip went hmmmmmmmmm.

If it had a blocked filter wouldn't the plug be a tad on the dark side or sooting up instead of looking horribly lean.

Mc Bob.

 

[pbtree]

If it had a blocked filter wouldn't the plug be a tad on the dark side or sooting up instead of looking horribly lean.

Mc Bob.

That was my initial thought - normally when you run a dirty filter, I would imagine that things richen up...

 

[Lawn Masters]

That was my initial thought - normally when you run a dirty filter, I would imagine that things richen up...

Logically thinking, yes. but of course, with Stihls Intellicarb I dont know for sure.

 

[havvey]

plug

Thats what i was wondering:yoyo:

I wonder where all the little bits of molten metal that belonged to the plug tip went hmmmmmmmmm.

If it had a blocked filter wouldn't the plug be a tad on the dark side or sooting up instead of looking horribly lean.

Mc Bob.

 

[klickitatsacket]

the ignition was advanced to far would be my guess, but with out knowing exactly were you set it at, it's a little tough to tell.

 

[lesorubcheek]

Yea, I'd agree with Dean. The only other thing I could suspect would be a bit of the dirt made it through the filter and clogged the carb jets enough for it to run lean. I've never had this happen on a saw, but my mower has clogged before.

Dan

 

[Kenskip1]

Diagnose this??

First off, what make and model is the saw?If memory serves correct, the timing is permanently set on Stihl. How old is the saw? It may have sat a long time.The plugs color looks as it was running fine. How about just a bad spark plug?I would simply pull the muffler and make a through inspection and look at the cylinder. Of course I am sure that you have compleated this task. Ken.

 

[NWCS]

Dean nailed this one. timing too far advanced (about 8 degrees from stock)
its now backed down to my normal spec.
Stihl 044BB woods port.

this is the second plug i know of from the same batch that has had issues.
the other one came apart while pulling the plug boot off, center wire was still in the boot. this one the center electrode is missing to about 1/8" inside the insulator. no cracks or chips at all in the insulator. if this happens again i will not be buying any more Bosch plugs.

 

[ccicora]

What are you running for a fuel octane? No I don't want to start a fight But I am imagining the compression was bumped a bit to.

 

[buzz sawyer]

Any chance there was dirt on the plug seat or the plug was not fully tightened? That will cause an overheated insulator and burned center electrode. I've seen this on cars.

 

[NWCS]

chris: running prem pump gas. not sure what station he buys from. 92 oct i think it is. compression is not much higher than stock. now the 064 i built him that has around 195psi still has the same plug and runs the same fuel.

 

[watt]

This may sound abstract, but if the primary connections of the spark coil were reversed by mistake, it would cause the coil to fire in reverse polarity. This means the spark would jump "backwards", i.e. from the side electrode to the center electrode instead of vice versa as is normal. This would cause accelerated wear on the center electrode; BUT NOT in 6 hours of running! - watt

 

[buzz sawyer]

This may sound abstract, but if the primary connections of the spark coil were reversed by mistake, it would cause the coil to fire in reverse polarity. This means the spark would jump "backwards", i.e. from the side electrode to the center electrode instead of vice versa as is normal. This would cause accelerated wear on the center electrode; BUT NOT in 6 hours of running! - watt

Interesting concept. On cars with distributorless ignition, one coil fires two plugs - one normal and one reverse polarity and you don't see degredation like that. It maybe different with chainsaws. I have seen this type of damage when plugs were not fully tightened or the seat was dirty. The heat generated in the center insulator cannot dissapate to the cylinder head and the electrode melts down.

 

[watt]

Hi Buzz: Thank you for your comment. To be a bit more exact, not all cars with distributorless ignitions fire in reverse polarity. It is only the ones with the "waste spark" type of ignition system and then only one half of the spark plugs fire in reverse polarity. The cars (and trucks) with the distributorless ignitions sytems that use the coil over plug (cop) system, i.e. a dedicated ignition coil for each cylinder always fire in normal polarity. That is the spark jumps from the center electrode to the side electrode. This is the normal or usual manner. However, in cars with the waste spark system each ignition coil is connected in series with two spark plugs and one plug fires from the center to the side (normal) and the other plug fires from the side to the center electrode or reverse polarity. Spark plugs with very small center electrodes, i.e. platenium type, are much harder to fire when operating in reverse polarity. That is why standard type spark plugs are recommended and platinum type are not recommended in vehicles with the "waste spark" system. I hope I have not totally confused you! Cheers- Watt