Yamaha 200etln 2-stroke bad coil?

[Jprevat]

Pretty sure I have a coil going out but wanted to check with yall before I ordered parts. The way I ohm'd these was to attach the negative clamp to the lead going into the coil from the CDI and the positive to the contact in the plug boot.

They all read about 2.50k ohms but one came to 6.57m ohms. I'm assuming this is the problem coil.

I was running it on the hose and would get a heavy cough through the exhaust intermittently and the engine would idle up for a second before coming down again.

 

[Jprevat]

Quick video at idle.

 

[boscoe99]

It probably won't matter but I would retest the coil using the Yamaha specified procedure. From the ground point of the coil to the output lead to the spark plug. With the plug cap removed.

 

[boscoe99]

If the coil passes the test using Yams procedure, but does not pass using using your procedure, the problem might, repeat might, be in the connection point of the male bullet terminal to the wire. You might get lucky and find a poor connection that can be repaired. In lieu of buying a new coil.

 

[Jprevat]

Thank you so much for that. I will pull a few coils and bench test them to see what's really going on.
This engine sat far too long with no attention from the PO so now it feels like one thing after another.

 

[Jprevat]

So it turns out the wire inside the boot end of the coil was corroded. Seems like it still has the same surge in idle though. I'll be changing plugs before the weekend to see if that's my weakpoint before I take it in to have the carbs checked out.

 

[Jprevat]

This was taken right after the new plugs went in today. Seems much worse when engine is cold. Seems to be a fair bit of soot in the hub too. Starting to think the carbs are over fueling.

Rough Cold Idle

 

[Jprevat]

So I turned opened the mix screw a quarter turn and it is running much better on the muffs with minimal backfires. I'll give it another quarter turn tomorrow and see where that leaves me.

 

[Jprevat]

Reset all the carbs to factory spec and tuned until coughing through exhaust stopped. Idled great but after I let it sit for an hour and started back up coughing resumed.