Stihl 021 High speed jet?

[Don_N6CRV]

Hello, I have a Stihl 021 that seems to miss in the middle of a cut. It starts fine and idles fine. Seems to have good responce when goosed. It has a new plug and the air filter is clean. I don't see a adj for the high speed jet, is it a fixed jet? I pulled the plug and it was light brown on one side of the tip and darker on the other. Using Stihl oil mixed at 40:1 Any thoughts would be of help.
Thanks.....Don

[Kevin]

Hi Don;
Is the muffler and screen clean?
I believe the 017 had a fixed high speed jet and the 021 had an adjustable high speed jet.
Is that the original carb?

[incognitive]

The things mentioned sound good.  Depending on vintage it may have only the low-speed jet adjuster, if you don't see one for the high side then that's what you got.  Might try having a look at the tank vent to make sure it works okay.

[Don_N6CRV]

Hello Kevin, yes the muffler and screen is clean, I did add 3 1/4" holes to the front of the muffler but that did nothing that I could tell. I beleave the carb is original as far as I can tell. I do make sure that the chain is sharp and the bar is getting oil. It cuts good but you can hear the miss. It can keep up with a Husky Rancher 55 in all but the really big stuff so it must not be to bad of a miss. It is just that I know it should not be there. I can not tell you how old the saw is as I got it used but this is the second year that I used it. The piston looks good thru the muffler port but if it helps I do notice that it does have a kind of brown tint to it instead of silver as you would expect. I will check the vent on the tank. Thanks for the help
Don

[Kevin]

It could be a bad piston ring or a carb problem also.

[Preston]

Check your spark plug wire sometimes it will rub a pin hole in it and cause it to miss when it is warmed up! Another thing that might help is check your wiring on the ignition behind the pull cover! There has been times when I have gotten a saw after a few years the ignition went bad! It would start and runn just fine but after warming up it would start missing! That really sounds like thats what it is but not sure! Start with the plug wire! Ignitions usually never go bad but you always have that one that goes bad!!

[kenskip1]

Don,
 When was the last time you changed the gas filter? Ken

[jimc]

I've seen coils go bad where the insulation breaks down causing a hi speed miss-especially after things get heated up..
try closing up the plug gap (.015 or .010) . also try misting the saw with water while running - bad plug wire, terminal  or coil insulation test.
try another plug or put yours in another motor.
Try cracking the gas cap loose and running under a load -1/2 tank or less if your smoking.
Get an inductive timing light hooked up and you can check for ign. miss too,
Good luck

[Don_N6CRV]

Hello Ken, I never have changed the gas filter. Jim I will try the plug in another saw. Will also try cracking  the gas cap and see what happens. You all have been a big help.
Thanks Don