50:1 is actually richer than say 32:1 or 40:1, i didnt know that until just recently. When you talk about fuel mixture ratios, if you have one ''unit'' of fuel that has 1 part of oil and 50 parts of gas, then it would be richer than 32:1 for example because 50 parts fuel is more than 32 parts fuel per one ''unit'', if that is understandable. Reading the carb tuning guide on the main site will expain it better. So, I would try running 32:1 or somewhere around there first and see if that fixes your problem. Also, make sure your air filter is clean, because if it isn't, it will allow less air to get in while the same amount of fuel is being delivered, richening the mix. If all that doesnt work, just try dropping a size or 2 on your jets. Yet another reason to read the carb tuning guide under tech tips on the main site it is very helpful.