Mike, if it runs properly at all speeds and loads except idle, and the problem at idle can be overcome by applying some choke, the engine has lean mixture at idle only. That means either it has an intake air leak at idle only, or the carburetor's idle system is not passing enough fuel. Because carburetor engines have high intake vacuum at idle but much less vacuum at higher speeds, an air leak is a possibility, but you have worked on the intake system to eliminate leaks. So, the best bet is the carburetor's idle system. The Suzuki M120X uses a Mikuni BV18-15 carburetor, which is fairly complicated for a mower engine. As you know, it has an idle mixture screw, and you should try adjusting it to see if you can improve the idle. Do not take the "initial setting" too seriously in this situation. If you find the mixture screw can make it worse but not better, there is a strong possibility that you have not got all the crud out of the complicated idle system. I suggest you read this thread:
https://www.outdoorking-forum.com.au/forum/u...mp;Words=M120X&Search=true#Post50386Note that Toro recommends that carburetor maintenance for that engine consists mainly of soaking the carburetor (with plastic parts removed) in carb cleaner - you won't get all the crud out just by squirting the cleaner here and there, let alone just by blowing air through the passages. (Carb cleaner is powerful stuff by the way: if you haven't used it, you'll be surprised at its effectiveness.) The internet is full of reports of problems with that carburetor, and most of them seem to be consistent with them still having dirt in them, after conventional cleaning.
You need to put a proper paper air cleaner on that engine before you make any use of it. It is a good enough engine to deserve a reasonable chance of survival, which requires an air cleaner that works the way it should (including foam pre-filter, and paper filter).
