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Post by Wisconsin Terry on Oct 21, 2021 8:28:20 GMT -5
I have a 450 that I can’t seem to get spark. I disconnected the kill switch to verify that it wasn’t a problem and I checked the continuity of the other wires which turned out fine. I put an ohm meter to the original coil, which was the blue one, measured 220 ohms. I bought a used one online that measured zero so I struck out with that one. I found a “new old stock” black one online and it also measures 220 ohms and I can’t seem to get spark to the plug. In my other saws the ohm reading is around 8000. Just wondering if I’m missing something? This is starting to get very expensive. It seems strange they both measure exactly the same. I already tried cooking them with no change afterwards. Do I just keep trying to purchase another coil until I find one that works or is this a normal reading and there is a different problem?
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Post by edju1958 on Oct 21, 2021 10:36:49 GMT -5
The problem you're having with no spark could be caused by a bad transformer on the rear of the saw that covers the spark plug.Those have a tendency of going bad & they're tough to find & can be expensive as well.There's really nothing to a transformer either,just a bunch of foil wound up in a pile of plastic.A very poorly designed piece of equipment IMO.A transformer from a 360,450,550,etc.all interchange.
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Post by lesorubcheek on Oct 21, 2021 12:11:38 GMT -5
Checking for a failed switch was a great idea. So, the blue thing at the flywheel is actually referred to as a "trigger module". As far as I've understood, it's not testable using a meter. Here's a link that explains a good bit about the '50 series ignition testing:
As edu1958 said, the thing that covers the spark plug is a transformer. It can be tested with a meter since it's just a primary and secondary coil winding. The only ways I know to test a trigger module is either using one of the Homelite test lamps or by connecting a known good transformer like described in the link, and seeing if you get a spark. Oh, there's also some info on holding a neon bulb next to the transformer, but never tried that.
One more thing, on a 450, the trigger module is blue and this means it has a built in rev limiter. 450s all came with a fixed Hi jet carb and relied on the blue module to limit rpm. Black modules are unlimited and the tan modules are limited to a lower rpm and were used on the DM50 demo saws. Unless you change out the 450's carb with one from a 550 that has an adjustable Hi jet, it's not a good idea to put anything but a blue module on it.
Lots of time, it ends up being a poor connection either with a module ground, the wire running from the module to the transformer receptacle, or the tabs on the receptacle and contacts on the transformer. The transformer's tabs tend to bend down over time, oh and the spring inside that contacts with the plug tip can also get bent down or get corroded or trashed up. These are the areas I'd check first before Easter egging a different module or transformer. Good luck, you'll figure it out, these things can just take some time.
Dan
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Post by blythkd on Oct 21, 2021 19:16:04 GMT -5
I've found the transformer not making contact with the receptacle contacts on the saw frame more than I've ever found bad modules.
The rounded flange on the lower edge of the transformer is pretty good at getting caught on the rear shield of the saw, keeping it from seating up tight against the electrical contacts. I just ran into one of those a few weeks ago. It's best to push the lower edge of the module up tight before you tighten the screws rather than just hold the transformer up to the saw, start the screws and tighten them to seat the transformer. Kinda rock it in at an angle, pushing the lower edge up first until it bottoms out then push the top edge up tight then run the screws down.
Not saying it's your issue, but it might be worth a look.
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Post by lesorubcheek on Oct 22, 2021 16:35:28 GMT -5
I've found the transformer not making contact with the receptacle contacts on the saw frame more than I've ever found bad modules. The rounded flange on the lower edge of the transformer is pretty good at getting caught on the rear shield of the saw, keeping it from seating up tight against the electrical contacts. I just ran into one of those a few weeks ago. It's best to push the lower edge of the module up tight before you tighten the screws rather than just hold the transformer up to the saw, start the screws and tighten them to seat the transformer. Kinda rock it in at an angle, pushing the lower edge up first until it bottoms out then push the top edge up tight then run the screws down. Not saying it's your issue, but it might be worth a look. Perfect recommendation! Dan |
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