Chainsaw Repair

I was trying to get two Stihl FS 130 brushcutter engines going. But both had the same issue. Starts fine, accelerates at WOT, starts leaning at partial throttle, release throttle, they idle, rpm gradually
drops  and engines stall as if running out of fuel. Tried different carbs, coils. No use. Ran them without their mufflers and things improved. No mufflers are not clogged.
After stalling starting with choke does not work, i need to squirt fuel into the carbs or directly onto the piston after removing the plug. I realised they run fine if I have their mufflers removed.
Ok my fuel is at 25:1 or maybe a bit more oil.
Could this be the reason? Not being an engineer, school physics seems to suggest SVP.  Could this be the reason caused by high oil content. Since these engines have dry crankcases they have some similarities with two strokes. I think I have had a similar headache with a tiny 23 cc Makita top handle. I even replaced the carb but no improvement. Compression and spark good, new seals. I gave up a few years ago. I need to locate it and see if it runs without the muffler

Maybe I will try it with half the oil.
But, I usually see this in the  smaller  2 stroke engines, like that 23cc Makita top handle chainsaw (Was searching for it today, unsuccessfully)