I have one of the more recent models with four corner idling (I think it is a 4150 model, I bought about 10 years ago new). I can only adjust the idle screws a 3/4 of a turn out then she starts to shutter and run like crap, even though they suggest starting with them out 1 1/2 turns to start? It idles great the way I have it set up now with the idle mixture screws but just seems odd.!? I have had the carb apart to clean and change the jets and squirters, found some rust debris in it from the old tank, I had hooked up previously now that and the fuel line has all been changed out. I may go with a thermoquad but will have to change my intake to do so, I'm not sure at this point? Thanks for all the information everyone!