Non-Slip thumb throttle

Howdy ya'll. I am working ona 2000 Yamaha Breeze 125. It was in rought shape when I received it and I am working through issues as they pop up. The quad had been sitting for years. I was able to get her running again, but I need your help with the following issue:
I don't trust the transmission yet and I don't want to make problems any worse. So, I haven't pushed things hard at all. Low rpms, less than 5mph in reverse.

Nuetral: Runs as expected
Reverse: She seems to be driving fine at slow speeds. Going into reverse at idle is fine, coming out of reverse back into neutral won't work (the shifter is just stuck). As soon as I turn off the quad, I am able to shift around without any issue.
Forward: It slips. It seems to only transfer power to the wheels on a smooth surface and going slightly downhill. When shifting into forward at idle, there is a clacking sounds during the transition. Shifting back to nuetral works just fine.

Other Notable Symptoms: There was old oil in the vbelt and when I was tuning the carb, it starting blowing out of the CVT cooling vent at the front of the quad. Made quite a mess. There is positive crankcase pressure due to piston blowby, that I have not decided whether or not I am going to fix (customer budget dependant).  Since the oil was old, much darker than the new oil that is in the crankcase, I am thinking it seeped past a bad seal while it was sitting for years. The oil that was in it when I first got it had gas in it.

Thoughts: I am thinking maybe there is an issue with the clutch. I worry about the old oil intermingling with the dry centrifugal clutch. I was thinking my next step would be to take the cover off of the clutch and inspect it.

Let me know what you all think. Any advice and ideas is greatly appreciated. This is only the 3rd quad I have worked on and I have a lot to learn.

Lorne

The 2026 Muddy Creek ATV Motocross National Championship (ATVMX), an AMA National Championship, delivered an unforgettable weekend of racing in Tennessee, combining intense on-track action with a meaningful tribute to one of the sport’s greats, Joe Byrd.View the full article

Okay so I bought this 1997 sazuki king quad from a guy and he had it for a few years. 
He had it registered and on the trails last year but he said it bogged and backfired when he would try to drive it. so it sat for a year. 
I bought it for 800 bucks and got it running that night and it ran great for a few days 
But I parked it the other night and went to start it again and it was really hard to fire up and when I did it was bogging and idling high then low again.
So I took the carb out and cleaned it (ended up doing it twice because it was still doing the same thing) 
Now today I have it running slightly better, but it is still like 20% 
I have been looking it up and trying to figure it out but I can't find the issue, has anyone else had this problem? I'll attach a video of it running and giving some throttle 

Hey everyone, I just replaced the carp on my 98 Kodiak 400 with PN#4SH-14101-00-00. It starts and idles perfect, but once it’s good and warmed up, it bogs out at 3/4 throttle or more… it sounds like it’s bouncing off a rev limiter haha… I tried the air fuel screw, all the way in and out 2-1/2, and it made it a touch better… tried 2 turns and no different. Am I missing something?

Anyone have an assembly? Thumb throttle and cable to carburetor?