So my 1981 mx175 is doing the missfire idle and if I give it any gas Boggs out and is flooding. So I’ve cleaned the exhaust new coil and plug and  changed the 2 coils on the plate but my question is how important is the coil lighting 1 the bigger copper one ? I haven’t replaced that. 


 

Lighting won't matter like the older points models which had the points source coil earthed through the lighting coil.
You say "Bogs Out" & is flooding. So do you mean goes super rich untill it stop then fuel pouring from somewhere--carb.
Or is it gasping as in lean & getting air but no fuel so it stops.
Sorry i'm reading between the lines.
So was it doing this before the coils & parts swapping.
Could it be a crank seal?, Right side & she'll smoke badly & be gaspy on the throttle if it runs at all.
Left side just gaspy or if its blown right out of the case it won't even try to run from my limited experience.
Possibly left side on yours is well retained by the stator plate but not sure without looking.
Anyway, you changed coils so that would be obvious if out.
Right side will have a retaining steel plate covering part of it but if its been flooded with 'a lot' of fuel in the crankcase--[not talking trans case]--but crankcase with fuel left on & a carb float valve fault then it'll overflow into the motor.
Kicking with lots of fuel in there can force the seal out & bend the plate on the right side. Anyway--all a wild guess on my part. Need a bit more info please.
In saying 'that' i think MarkT is hot on ignition faults of those--if it 'is' ignition.
Just stretching my imagination a bit further you say the big coil. The parts pic on cmsl shows only one big coil which is ignition & i doubt in reality that its as big as the parts drawing shows.
It doesn't show a lighting coil at all on the plate.
So yours does have a lighting coil? If so, then you've replace the ign source & the pulser little coil? So should be all good, plus ya did the plug coil & plug.
In theory it only leaves the cdi box. I'm not saying it's 'that' but they're generaly reliable boxes on yamaha.
images.cmsnl.com/img/partslists/yamaha-m...gyau0944a-8_645e.gif
Parts list shows a pic of what id expect to find with #4 below.
www.cmsnl.com/yamaha-mx175-1981-b-usa_mo.../partslist/A-08.html

So yes the bike will fire up first kick Iv replaced the cdi box and no difference the pulse coil and the other coil that’s not the big copper one. The seal looks ok on the left side. The bike has fuel coming out of the exhaust it will idle but any rpm it’s misfires and just Boggs out. 

OK I now think it's severely flooded up if you have fuel coming out the exhaust. So seeing it will start, just restart it but DONT open it wide open & drown it but slowly very slowly bring the throttle up. That's if it will run slowly in the first place.

Sorry I've been away for a few days...  I've seen this before and I can tell you it's not the CDI box.  I suspect it has something to do with stator or flywheel but changing stator components did not work.  It is not uncommon on that model.

But just to make sure, here's a video of the problem I spent hours and hours trying to fix for TerryM.  It's definitely ignition even though it sounds like it's flooding.   

I installed his ignition on my good running 175 and had the same "flooded" running.  We got Terry a new ignition and his MX175 ran perfect again. 

Here is a quick video showing how bad ignition would start and idle but bog out under throttle.  Then run fine with different ignition. 




 

Just to add a note after watching video again...  my "spare" MX175 ignition had both the source and pick up coils replaced.  Doesn't bog like it did but still runs erratic as heck and has no power.

From other threads on here...  the MX175 ignition in 80-81 appears problematic.  I've personally only seen one that didn't act up out of about 5 or 6 bikes.  In contrast, I've seen and owned many of the 80-81 DT175 CDI's I've never come across a bad one.  (Same CDI box so it's not that)

Hey thanks terry the video is exactly what mines doing so I did the ohms test on pulse coil it was within spec the other bigger white one the source  coil ? It’s supposed to be 300ohms plus or minus 10 percent both of mine are reading 250 ohms assume that my problem. 

Good luck.  A new source coil did not fix Terry's stator  Did not make any difference at all.

Here's the specs.  Note the temp and generally Yamaha used "analog" meters which sometimes read different than some digital meters in my experience. 

I just listened to the video which I realize isn't yours but if yours is running like that which sounds like 8 stroking which is pretty much what kids PW50's do on the start possition for safety. So are you by any chance running a cdi box of another model with a red wire left over spare.