Trying to read plug condition--on a 346xp

[old CB]

I bought this 346 as a non-runner, put a new p&c in it, and new crank seals and carb (OEM). It’s just now about broke in—8 or ten tanks of fuel thru it.

Been working up around 8,000’ elevation, which I thought maybe accounted for the weird tuning issues. But yesterday it was running like dog crap and I shut it down. Pulled the spark plug today to look inside. I’ve never seen a plug like this. One side—about 40%—and the tip of the curved electrode is nicely tan, looking like a clean burn, but the rest of the thing is gunky black.

I burn pure gas, no ethanol, mixed at 50:1 (plus some, probably 47:1) with Stihl Ultra.

Any idea what causes this condition?

Also--it's a Champion plug RCJ7Y, so I replaced it today with a Bosch or whatever I had around. I don't trust Champion anymore. Seems like the new plug was better, but I only ran it a few minutes.

 

[Full Chisel]

Put an NGK BPMR7A in it and cut wood.

 

[old CB]

Cool. Thanks. Seems like it ran right with a different plug, but I won't know for sure till I give it some work time.

 

[schmauster]

+1 NGK. Champions arent known to be great plugs. Are you retuning it at the elevation youre working at?

 

[blsnelling]

Forget plug color and tune it by ear.

 

[old CB]

I now keep NGK plugs on hand--they're all I use.

Thanks, Brad. I do tune by ear. But am still baffled by that plug I pulled. Never seen one unevenly colored like that. Curious about what would cause such a condition.

 

[Ryan'smilling]

NGK, and ditch the ultra.

 

[Brushwacker]

My guess is you are running rich, at high end under load it cleans up some from a hotter burn. I've seen more then a few plugs similar in color to what you describe. Even if it looks clean make sure your air filter is breathing properly. Take it off and see if there is a dramatic difference in acceleration and wide open throttle. Those type filters some times seem to glaze up rather then fill up with debris. Other then that, carb adjustment or something defective may cause it to run rich. You might better take a look at your pistons condition through the exhaust also if it doesn't clearly run right after trying the simpler things.

 

[old CB]

Interesting that you mention the air filter. It looked immaculate, but I tried the saw with and without the clean filter and it ran much better without. So I bought a new filter which made quite a difference. I could not see anything in the old filter, but somehow it was restricting air flow.

 

[Brushwacker]

Interesting that you mention the air filter. It looked immaculate, but I tried the saw with and without the clean filter and it ran much better without. So I bought a new filter which made quite a difference. I could not see anything in the old filter, but somehow it was restricting air flow.

I think worn rings ( possibly from the previous top end ) have something to do with letting some fuel spit back through the carb which may have dried up restricting air flow.

 

[Little Al]

Unless you do a correct plug chop the colour of the plug is meaningless any run on from the chop will give a different reading ,doing a proper chop is pretty much a No Go as a saw does not have a mechanical means of freeing the clutch without motor run on at ignition kill ,which makes the chop a waste of time. As Brad says a more reliable method is to tune by ear. Different oil blends used at same ratio also affect the plug colour dependent on the amount or other wise of additives? castor bean oil the famed Castrol "R" will at the best mix for max power running will give you the dirtyest/oilest plug you"ve probably ever come across, but the motor will perform better than the 1000/1 all singing all dancing synth that keeps the combustion chamber "squeaky" clean But in a lot of cases fashion seems to rule over known facts of 2 smoke performance but 'Hey Ho' each to his own.

 

[old CB]

Yes, I'm told that you'd have to kill the motor in an instant to get a correct plug color reading. However, when I pull a plug and it's gunked up black, or nicely clean and tan-gray, it's hard for me to believe that either condition was produced in the 6--8 revs (or whatever) since I hit the kill switch.

So I look at the plug color as an additional indicator, not as a guide to tuning. I tune by ear, or using my tach.

 

[old CB]

I think worn rings ( possibly from the previous top end ) have something to do with letting some fuel spit back through the carb which may have dried up restricting air flow.

Yeah, that makes sense. I could not imagine what would make a clean-appearing filter get in such lousy condition.

 

[blsnelling]

Unless you do a correct plug chop the colour of the plug is meaningless any run on from the chop will give a different reading ,doing a proper chop is pretty much a No Go as a saw does not have a mechanical means of freeing the clutch without motor run on at ignition kill ,which makes the chop a waste of time. As Brad says a more reliable method is to tune by ear. Different oil blends used at same ratio also affect the plug colour dependent on the amount or other wise of additives? castor bean oil the famed Castrol "R" will at the best mix for max power running will give you the dirtyest/oilest plug you"ve probably ever come across, but the motor will perform better than the 1000/1 all singing all dancing synth that keeps the combustion chamber "squeaky" clean But in a lot of cases fashion seems to rule over known facts of 2 smoke performance but 'Hey Ho' each to his own.

Additionally, the part of the plug that needs inspected is the very base of the porcelain, way down inside the cavity. What most people look at is the tip, which is coloured by idle/midrange.