125-200cc 8 miles per plug, this is getting old...

Yep the 3rd one I tried in Bens bike, it lasted 30 seconds. I may try another one and put it in a bike that is all warmed up. If that doesn't work the plug cleaning tool may not get used much.

It is getting narrowed down, but still has been a frustrating guessing game.

I already replaced the plug cap... Stock and NGK are both 5kΩ resistor caps.

Later,

Did you check the kill switch wiring? I cant remember if you mentioned that or not.

It wasn't the right side crank seal...

9 miles tonight, fouled after about the 4th heat cycle.

Tear it down tomorrow to put a ring in it, change the reeds, and pull the kill switch.

Still runs great, until it doesn't.

Later,

Damn Jake this motor is snake bitten. I imagine when the problem finally is solved it will be an interesting cause, doesn't make it better just interesting.

Did you ever try trying a hotter or colder plug? Maybe the motor needs a 7 or 9 heat range to stop fouling...

Another WAG, what about the needle and seat? Could they not be closing properly? Did you double-cehck the float height?

Worth a shot, at this point if you told me you were 25.6% certain that changing my rear tube would fix this issue it would be worth trying...

My cap is an aluminum tusk cap with the short vent hose with the aluminum cap, it is worth a shot.

I am constantly thinking about this thing, wondering if it has a loose case bolt and is pulling oil between the case halves when sitting. Or if it has a pourous casting or something.

I changed the whole carb, doesn't everyone have a spare TMXX laying around? :-)

I checked the float height on both carbs, they are both set at 8mm. I don't get any leaking out the over flow on either carb.

Later,

have u tried swapping complete motors from a spare bike, and leaving your electrics?

I am 25.6% sure it is the rear tube... Interested to find out how this ends. Good luck and keep up the posts

No that is crazy talk, I put all my electrics on a different bike and it ran fine...

Later,

As a side note I have got to spend some quality time riding with my nephews. This field is what I grew up riding in from the time I was 5 years old. I have many many miles riding around in circles out there, it can get old at times. I realize though just how lucky I am to have this available to use 2 miles away from my house. My brother bought the property from my parents and had 4 kids that are growing up just like we did. If I had to load up and drive to a riding area there is no way I could justify changing one thing at a time to figure out the exact cause. I would have gone with the shotgun approach, changed everything and hoped for the best.

I got this photo last night with my phone of my nephew airing it out on his xr80, he has been on this bike a little over a month and is really hauling the mail.




Looks similar to the one my dad took of me in the same fIEld almost 30 years prior...



Later,

Try a NGK BR9EIX

http://www.motorcycle-superstore.com/1/4/70/11064/ITEM/NGK-BR9EIX-SOLID---Iridium-IX-Spark-Plug.aspx

all i can suggest is to check and clean the powervalve mechanism and vent lines on the powervalve and engine.have not read through the whole thread so sorry if you have done this already.

I would try a hotter plug too, its not oil foul that kills them plugs i think. Heat range is important or they foul.

I have tried a 8 plug, it fouled it too. I think changing from the factory recommended plug is a band aid for a hatchet wound. I only used them because it is what people had to get me back to the truck.

Some photos from the tear down...

Odd pattern on the cylinder head?

Odd markings on the bottom of the cylinder...



Ring end gap is between .35 and .40... Checked above and below the ports.


Later,

Yea... That's oily and full of carbon. A hotter plug only releases less heat through the plug itself and is not going to help you here. Is that 2T oil or crankcase?

That is a strange burn pattern on the head and the oil head indicates you may have a crank seal issue?

PS..What the heck are those gauges int 4th pic??

I changed the crank seals, I wonder if it is pulling oil between the case halves, I pulled the stator tonight and tightened the case bolts as a test.

I am still confused, it has never smoked like it had a crank seal issue. I was told to put some castor oil in the crank case and I would be able to smell it if it is burning crank case oil. I still don't think it is fixed... Just pulling the plug after a 5 minute warm up with the new ring it didn't look great.

I believe the gouges in the 4th picture are where they grind the seams from casting, I have seen them in every one of these 125 engines I have had apart.

The compression numbers are up though. I may try to ride it tomorrow if the rain holds off a bit.



Later,

Oh Jesus, here we go.. Another fair weather only rider...