“Coming in” speed for chainsaw mags (coils)

[av8or3]

Observed a very interesting phenomenon today repairing a Sachs-Dolmar 166 ignition. Always when starting this saw cold I would wear myself out trying to get spark. Once the saw popped and started it ran fine. Easy peasy to start hot. It’s a free standing coil ignition so it’s Really Not rocket science. It either works or it doesn’t. I was convinced it was intermittently failing, although it never quit running on me. Well, thanks again to a member here I was able to score another coil for my 166. Believe me, it was like Christmas, again! I first checked the old coil for spark by grounding the threads of the (pulled) plug against the cyl fins and yanking the starter. Nothing, took the ground wire loose to eliminate the switch.Still nothing.
Removed the recoil to access the coil and decided to spin it up with my drill before removing it. NOW got spark. Hmmm. I snapped the recoil back on and gave it a mighty tug and got nothing. I replaced the coil with one supplied by the aforementioned member and now I got hot blue spark when I’m tugging on the starter. The original obviously wasn’t happy unless it was spun up pretty fast when first started. I just couldn’t spin this thing up fast enough. After running I was tickled to death. It popped on the 4th pull (tank was bone dry before I filled it) and started on the 6th. Ran like normal. It’s an interest failure. Either the coming in speed for the original coil “moved” or something and the replacement coil fixed the problem by coming in at a lower speed. After this afternoon I’m convinced the saw will be much more user friendly.

 

[Chevboy0167]

I take it that saw has CDI ignition yes?

 

[av8or3]

I take it that saw has CDI ignition yes?

No, it does not. Just a stand alone coil.
Also, I adjusted the air gap down to specs on the old coil previously hoping that would help. It didn’t. I’d be very interested in what happened to make it change. It’s a potted coil, probably not much different than modern ones. Something inside just went bad I suppose.

 

[Old2stroke]

No, it does not. Just a stand alone coil.
Also, I adjusted the air gap down to specs on the old coil previously hoping that would help. It didn’t. I’d be very interested in what happened to make it change. It’s a potted coil, probably not much different than modern ones. Something inside just went bad I suppose.

By "stand alone" coil I presume it is an electronic module coil and no breaker points? This is a fairly common failure mode, the sensitivity of some semiconductor component in the coil is slipping and it no longer produces a spark at low rpm. Have seen it a lot and currently have the same thing with a Poulan PP5020.

 

[buzz sawyer]

Had the same problem with a ProMac 1010. I even reduced the coil gap to .005. Replaced the coil and it was fine.

 

[Chevboy0167]

In other words, yes on the CDI. Capacitator Discharge Ignition. To the OP problem with the old coil, he found no or weak spark until using a drill spinning the engine up. That would indicate a weak Capacitor not fully charging. Or some internal shorting of the enameled coated wire for the coil.

 

[TLG]

Another nice piece you have there sir.
You got a nice honey hole down your way Jim. Thx for posting the saw and issue.

 

[av8or3]

In other words, yes on the CDI. Capacitator Discharge Ignition. To the OP problem with the old coil, he found no or weak spark until using a drill spinning the engine up. That would indicate a weak Capacitor not fully charging. Or some internal shorting of the enameled coated wire for the coil.

Thanks for the explanation. I didn’t know it was CDI , I really always just thought it was magic going on inside one of them. Are all the modern stand alone coils CDI’s? I always thought there was an electronic brain inside that pulled the switch’s , etc. but it never occurred to me it was a CDI. And for some reason I always thought CDI was old technology. Anyway , thanks again.

 

[av8or3]

Another nice piece you have there sir.
You got a nice honey hole down your way Jim. Thx for posting the saw and issue.

Thank you.

 

[Old2stroke]

Thanks for the explanation. I didn’t know it was CDI , I really always just thought it was magic going on inside one of them. Are all the modern stand alone coils CDI’s? I always thought there was an electronic brain inside that pulled the switch’s , etc. but it never occurred to me it was a CDI. And for some reason I always thought CDI was old technology. Anyway , thanks again.

There are many different circuit that control the primary current to produce the secondary high voltage. CDI is just one of them.

 

[Chevboy0167]

The capacitor and transistor switch are built internal into the coil. Hence there is not a quick way to do a proper test with a multimeter on the ohms scale. Unless of course you have a test bench setup with a powered flywheel.

I call it CDI but I may have my terminology wrong.

In a breaker point style, the points are the "transistor", mechanical style switch. And the condenser is basically a capacitor.

I have looked for hrs trying to find a cut up small engine coil to show the internals with little success.

 

[Old2stroke]

The capacitor and transistor switch are built internal into the coil. Hence there is not a quick way to do a proper test with a multimeter on the ohms scale. Unless of course you have a test bench setup with a powered flywheel.

I call it CDI but I may have my terminology wrong.

In a breaker point style, the points are the "transistor", mechanical style switch. And the condenser is basically a capacitor.

I have looked for hrs trying to find a cut up small engine coil to show the internals with little success.

If you go to the trouble of cutting one up, you won't see anything that is recognizable, too many tiny semiconductors and other components. The only way to see what's in there is to dissolve the potting compound which is usually epoxy and is VERY hard to dissolve. Chloroform is the only chemical that seems to work, takes forever and is EXTREMELY hazardous.

 

[Bob_w]

If the secondary has a shorted turn it will measure just about the same, 2k ohms or so, but the power will be drained significantly. Most all of these machines have a capacitor discharge ignition. I used to work for a coil manufacturer.

I think I killed one of my huskys, by spinning it without fuel .... you need the oil. yep I cut a socket, and made it go with a drill. Scratched a piston, I think.