139qmb starting trouble, valve adj oil on spark plug threads

[Sir Scoots-A-Lot]

I have been having trouble starting my scoot the last 2 days. Before that I was changing the jetting and a/f mix, stock 50cc cylinder/head #32 idle #94 main jet very free flow air filter. The last 2 times it started were pretty easy, one time took  maybe 4 tries cranking with the a/f mix about 3.5 turns out and jet needle one notch rich out of 5 possible positions. The last time it started took only 2 quick cranks and I adjusted the a/f mix to about 4.5 turns out before it started. I had installed the #94 main jet about a week before because I was supposed to put in a 72cc cylinder which didnt happen. Before changing the main jet form 85 to 94 and jet needle position to one notch rich i was having a lot of trouble starting it but when it started it would run fine. After rejetting it seemed to start easier and idled alright but bogged/just didnt go badly under any real throttle and my top speed was down to maybe 20- 25mph but I was thinking that was just because the main jet was too big and I thought no harm I will either change cylinder soon or jet it back lower when I got time. I also noticed a mettalic rettling noise starting a week or two ago and I was thinking maybe it was coming from the cvt area, possibly the Bendix starter gear but not sure. So two days ago it wouldnt start after 45 mins cranking and seeing a backfire flash thru the carb and havent been able to start since although in 1 or 2 subsequent sessions trying to start after that it sounded like it was struggling to combust but was weak and needed more throttle to speed up and really catch which didnt happen--then after that Last night I decided to check valve clearance and I found them a bit loose being able to push at least a .005" gauge in the lash snugly so I went to tighten them to about .002" intake and .003" exhaust...tried to start it and sounded normal at first but wouldnt start after 3-4 good tries cranking. I cranked it again and I heard a bad noise kind of like metal hitting metal from either coming out around the carb area or cvt maybe the Bendix if I had to GUESS. I cranked a couple more times with mixed results of the bad noise and normal crank noise but no louck starting. I had pulled the spark plug to double check spark when I was doing the valve clearance before trying to start it up again and the plug sparked ok and looked well worn maybe a little on the dark/rich side with some build up mainly not on the insulator but on the other parts and thats all I noticed of the plug at that time. After finishing adjusting valves (which I noticed both in and ex could squeeze in at least a .005" gauge) and hearing the bad noise I checked the plug again to see if it was wet or fouled and I noticed what appears to be a grayish/dark mix of oil gas and crud on the spark plug threads. I was going to tear the head and cylinder off today to see if I can see a problem with the head/cylinder/piston or rings but its raining too much so had to put it off. Now my wuestion is why is there that oily mix on the spark threads that I hadnt seen before the valve adjustment? I opened the valves again and the intake looked like maybe I made it too tight with barely any clearance, if any at all and exhaust at about a tight .003".

Could the intake valve not having any setting clearance cause the valve to hit the piston, let oil in thru the valve opening, are my valve oil seals maybe going at roughly 18k hard miles and 5-6 years on the engine or maybe it is my piston rings are shot? could i have hurt the engine by running the main jet quite rich for a hundred miles? I have a new plug, battery, cylinder/piston/rings/gaskets/valve oil seal bbk I will be installing asap when time/weather permit me to, but in the mean time I really really appreciate hearingany thoughts or experiences you all have had on this subject.

thanks and happy scooting

-Presto

[FrankenMech]

Review the vids here on how to set the valves.

Your carb idle screw seems to be too far open. It should be 1-3 turns.

Check your enrichment valve operation.