Makita 7300p / Dolmar DCS 7301 ignition issues

[delooper]

Greetings,

I have a Makita 7300p which I believe is also a DCS 7301. It's a fairly lightly used saw that recently developed an ignition issue.

Carburator works great, the cylinder fills up with a nice fine misting of carburated gas when you pull the cord. The spark plug is new. It throws a spark -- but the spark looks weak. You sometimes hear one spark catch, but then nothing.

The kill switch works perfectly. The exhaust filter / muffler is clean. The fuel filter is clean and works great.

I think the problem has to be the ignition coil. Does anyone know if there's a reasonable way to bench test the coil? I pulled it out today but it's unclear to me how it should perform. It appears people mostly do resistance tests on them but I don't know what to compare it to. I have a new coil on order, so at worst, I'll be able to compare it to a new coil. But it looks like the part number has changed so I likely won't be comparing apples to apples. The item I ordered is coming with a different flywheel.

Any sage advice would be welcome.

 

[Rob Stafari]

Try a different spark plug. Had one show up with a brand new NGK in it doing the same thing. Finally tried a different plug from a known runner and it fired right up. Threw the brand new plug straight into the trash can... I was about to swap coils till a friend who used to moonlight in a Stihl shop told me about all the new out of the box plugs he had problems with.

 

[delooper]

I've tried two sparkplugs in it, with the same result. I had a new NGK in it, and the original (NGK). Also tried cleaning off the original a bit. I have another new NGK on-hand but didn't think to try a 3rd plug in it.

If I have no luck with the new ignition coil I'll certainly try your suggestion. Would not have thought of that, thanks. Would make me feel silly buying a new coil if it's just the sparkplug.

I've only had trouble with this saw once before, and it was bad gas. Got fresh fuel in it. I've cleaned the carbs and replaced the gaskets. Running out of ideas.

 

[delooper]

The new coil arrived a couple days ago. Finally had time to get it in today. As you can see, it came with a new flywheel.

Putting the new coil in was mostly straightforward. Happy I had some automotive feeler gauges lying around, otherwise setting the 0.3mm gap between the flywheel and coil might have been a pain. Getting the little sparkplug holder through the coil wire and getting the insulator on it was a fussy little step, too.

I buttoned the chainsaw up shortly after this picture, and it fired up on the first pull. So I'm fairly certain it was the coil.

 

[delooper]

Is you look at my old coil picture (the 1st from the top) you see it slighly delaminating. But it's not rusting. What's going on there? Is that a manufacturing defect? Could that have been caused by overheating?