Stihl 021 Runs Great, Then Does Not Run At All

[BrokenStihl]

I have a very odd problem with one of my saws, and was wondering if the experts here can offer a possible solution.

The saw is an older Stihl 021.  It cranks right up and runs fine and cuts well, with no problems.  As soon as I turn her off, set her down a couple minutes, and go back to try to start.......NOTHING.  I am not choking the saw again, but just turn the switch back on, and try to crank.  No sign of wanting to fire at all. 

This happens every time I go to use the saw.  Thinking that maybe she is not getting enough fuel, I remove the filter cover and squirt a teaspoon full of fuel onto the filter.  Still, this does not coax her into firing or showing a sign of wanting to start.  I pulled the plug, and the plug looks fine.....i even wire-brushed and cleaned the plug electrodes well, but of no help.

Is it possible that when the saw gets warm, this affects the ignition, and causes a failure?  However, she runs great up to the point where I turn it off. 

Am I missing something here?  Any suggestions?

[beenthere]

Welcome to the forestry forum.

A squirt of fuel on the air filter?
I'd remove the plug and put a squirt (eye dropper squirt) in the cylinder and test if it is starved for fuel instead.

Then can also examine the spark plug to see what it looks like, and test for spark at the same time.

[old2stroke]

What are you doing with the throttle?  2-strokes do not like to start with the throttle closed.  When you start it cold using the choke, most carbs have a mechanism that partially advances the throttle and keeps it there until you release it by hitting the trigger.  There is usually a method of using this feature without closing the choke plate for hot starting, most common is to pull the choke lever full out and then push it all the way back in, some carbs have a mid point setting of the choke lever that will advance the throttle but not the choke.  Check your owners manual if you have one.  Sometimes setting the idle speed up to the point just below where the chain moves will provide enough throttle opening to start a hot saw without setting the throttle advance mechanism.

[old2stroke]

Showing my age here.  What do you mean by an older saw?  Real older saws used to have a throttle interlock button near the trigger, you would squeeze the trigger, hold the button in while releasing the trigger and the throttle would be held partially open until you hit the trigger.  This was a foolproof system that was too easy to understand so it had to be changed.

[Texas-Jim]

old2stroke the new stihls have a throttle advance as well, when take choke up one notch it keeps saw revved up. But he is correct many saws do not like starting at idle.

[OH logger]

sounds like the ignition coil to me. does it start after you let it cool a while?

[BrokenStihl]

beenthere.......thanks for the reply.  Yep, on all my saws I will squirt some fuel mix on the air cleaner, then do the usual settings, and the saws start with one pull. 

The Stihl has the choke position, then the fast idle position, and then the normal idle position.  After she has been running for awhile, you should be able to turn it off for a few minutes, and then just turn the switch from "off" to low idle, and pull the starter rope once.  Now, once she is warmed up, she shows no sign of a desire to fire and start.

[BrokenStihl]

What are you doing with the throttle?  2-strokes do not like to start with the throttle closed.  When you start it cold using the choke, most carbs have a mechanism that partially advances the throttle and keeps it there until you release it by hitting the trigger.  There is usually a method of using this feature without closing the choke plate for hot starting, most common is to pull the choke lever full out and then push it all the way back in, some carbs have a mid point setting of the choke lever that will advance the throttle but not the choke.  Check your owners manual if you have one.  Sometimes setting the idle speed up to the point just below where the chain moves will provide enough throttle opening to start a hot saw without setting the throttle advance mechanism.

old two stroke....Yep....my Stihl has the low idle, fast idle w/o choke, and then the choke setting.  Starts fine when cold, but will not start after warmed up.

[BrokenStihl]

sounds like the ignition coil to me. does it start after you let it cool a while?

OH Logger.....thanks for your input.  So, you think the coil could be acting up AFTER it warms up?  What is the best way to check the coil?  Maybe pull the plug, and leave the plug wire attached, and then set the base to the metal engine block and pull the crank and look for a spark?

[BrokenStihl]

sounds like the ignition coil to me. does it start after you let it cool a while?

OH Logger......Yes, after the saw hass totally cooled off, she starts fine and runs good.  But if the coil is bad, wouldnt it show signs of poor performance while running? 

[XP_Slinger]

Not necessarily, a bad coil can do exactly what you described.  Its the heat that does it.  All coils get hot because they are nothing more than a giant resistor/capacitor.  If a coil is bad it can run perfect until the heat creates too much resistance for it to build and discharge when it is triggered.  I would pull the plug and check for spark when it won't start.  If the spark is bright blue you're good.  If it is orange, your coil is weak. 

[BrokenStihl]

Not necessarily, a bad coil can do exactly what you described.  Its the heat that does it.  All coils get hot because they are nothing more than a giant resistor/capacitor.  If a coil is bad it can run perfect until the heat creates too much resistance for it to build and discharge when it is triggered.  I would pull the plug and check for spark when it won't start.  If the spark is bright blue you're good.  If it is orange, your coil is weak.

XP Slinger.....Thanks for the input.  I will test the coil, and if that is the problem I will replace it.  I will follow up with the results.  Many thanks!  Looking for the Stihl to run again like it should.

[Texas-Jim]

Modern coils rarely degrade like that, they either work or they dont. I guess its possible but it be unlikely. Theres also no way that i know of to test a stihl coil, you can test fire but make sure its not grounding issue instead of coil.

[NYLoggerJim]

I had a faulty ignition coil act the exact same way years ago.  The engine would start easily and run like a champ UNTIL the engine heat warmed up the coil and the engine would die.  It would NOT restart until the ignition coil cooled down.  This cycle was reproducible so I replaced the problem was solved.  Prior to replacing the coil, you could check all the electrical connections and test the operation of the saw.  If it still fails, time to swap in a replacement coil.

Jim

[old2stroke]

Sorry to keep beating on the same theme, but it sounds like you are still trying to start the saw with the throttle in the closed or "idle" position.  Some saws just will NOT start without a fair amount of throttle opening.  Try this method just for a test; with the chain brake ON, hold the saw by the rear handle with your right hand and rest the tip of the bar on a piece of wood on the ground, then hold the throttle FULL OPEN and try to start it with your left hand.  Not an easy way to start if the saw has a lot of compression.  I have a few saws that will start first pull at idle just after being shut off, but give them a couple of minutes and they need some throttle opening to come alive.  I have a hard time believing it is the coil.

[BrokenStihl]

 

And update on the Stihl 021 that starts and runs fine, but after it is warmed up does not want to start.

The spark was real weak when it was warm, so I ordered a new coil.  The one I ordered was not a Stihl part, and I was really disappointed with the "exact part, exact fit" propaganda on Ebay.  The new coil was a bit smaller, and was lacking a wire coming out of the coil.  There were NO directions with the coil.  I had to assume that the extra wire in the package was just to go from the ground screw beside the flywheel to one of the coil mounting screws.  I tried it this way, and used a business card to get the right gap.  I then tried to start the saw, but nothing.  I checked the spark plug for a spark, and was getting a very weak and occasional spark.  So, I tried removing the extra ground wire that came in the package........after that, I got no spark at all.

So, I looked at the old Stihl coil and noticed that there were two areas of the coil that sit close to the rotating crank, and produce spark.  One of them was pretty grimy with oil/dust.  So, I was thinking that may have been causing the failure.  So, I cleaned it up real good, and put it back on the saw. 

Took it outside to use, and it ran great for 10 minutes.  I then cut it off, and once again......would not start.  Its not a lack of fuel getting to the cylinder, but definately a lack of spark.

So, it must be a bad coil, but the new one I got is also bad.
Guess I will have to buy a Stihl brand coil, and see if that works.

[BrokenStihl]

Old2stroke......Usually these Stihls will start with no problem after they have been running.  I typically just turn the kill switch back to "on", and pull the rope, and then pull the trigger a bit to idle up some. 

On this one, I did try clicking the throttle control to the next position, which is the "half-choke" position.  Still, no hint of a spark to ignite the mixture.  I even tried squirting a teaspoon of fuel on the air filter.....still nothing.

[old2stroke]

Looks like you have zeroed in on the problem.  Have you tried CHAINSAWR (one of the sponsors) for the right coil?  He has been a huge help in finding ignition parts for me.  Always the right part and a reasonable price.

[XP_Slinger]

Looks like you have zeroed in on the problem.  Have you tried CHAINSAWR (one of the sponsors) for the right coil?  He has been a huge help in finding ignition parts for me.  Always the right part and a reasonable price.

I'll second the  Chainsawr recommendation.  Ive had nothing but success when getting parts from them.  Glad you've narrowed it down and are on track to getting your saw running properly.

[BrokenStihl]

Thanks XP and Old 2......will check out chainsawr's site for parts.

Still scratching my head about this coil issue.

[limbwood]

You might try a new plug just for the fun of it, you never know.

[XP_Slinger]

Thanks XP and Old 2......will check out chainsawr's site for parts.

Still scratching my head about this coil issue.

How so?  Because of the bad Fleabay part?

[nuke1]

i'm an old fart but I can't get used to the idea of squirting fuel on an air cleaner instead of in the carburetor or in the cylinder and unless it's a brand-new air cleaner Im just thinking about debri

[Kuzuryuu]

Hi! I know the topic is quite old but given that I have the exact same problem i took my chances. Did you solve the problem?

Thank you very much!

Victor

[Old Greenhorn]

This is an old thread but for anyone who comes across it I just wanted to throw in this thought because I would bet a nickel it may be a solution. CHECK THE PLUG! If it is not a resistor plug, find a resistor plug and change it. The is a classic sign. Resistor plugs will have an "R" somewhere in the part number. It's a simple 2 minute $4.00 thing to check. Good Luck, Tom