You need to do more than "wash out the bowl".
Remove the hex plug from the bowl casting to access the main fuel jet hidden behind the plug.
The jet itself requires an Allen wrench to remove it from the carb.
Remove the jet and clean out the jet and the carb passages with spray carb cleaner.

Depending on the type of carb on your Twin, it may or not have an adjustable float. See the image below to see which type you have, and how to adjust (if adjustable).

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this is an earlier model of the opposed twin. Most of these had an adjustable main mixture and an adjustable idle mixture.

Your description indicates a lean idle mixture.
The idle mixture is located at the lower base of the carburetor. Use a common screwdriver to open this about 1/4 turn. See if there is improvement. If this engine is on a riding mower, the mixture screws may be difficult to locate because of the mower hood and grill.

These were great engines. Consider cleaning the cooling fins to avoid overheating.

Both excellent posts above, by the way, I have never seen a carb on a 42 series engine that was not adjustable nor any of its' counter parts, 40 series (L head), 46 series.

IF original, the carb will have adjustable main and idle jets.

Walt Conner

Thanks for the suggestions. I'm a Wheel horse person and usually tinker with Kohlers. I'm sure the passages are as clean as I can get them, I did adjust the float level lower thinking it was flooding out. I can't find any kind of adjustment screw for air/fuel mixture. There is a low idel screw but it just acts as a stop for the throttle shaft. I'll adjust the float to level as indicated and see if that helps.
Thanks again for the pointers.

The idle mixture screw will be sticking straight out at you when facing the carb at the base of the carb. The main metering adjustment will be on the right side, base of carb sticking up at an angle. (IF it is the original carb)

Walt Conner

I am having a problem with gas overflowing into the intake manifold and into the left head. I will adjust my float one more time based on what I read here.

Dont forget to check the float for leaking and filling with gas. I had one that took a long time to fix,as the float had a small leak. After adjusting it,cleaning everything,new kit, I did shake it to check for gas in it and I couldn't hear or feel any gas in it. It would run ok,then if you let it set,it would flood. Since this was a back up mower,I would let it sit a week or so and try to figure what was the trouble. So for the fourth or fifth time I took the float off and was very careful when I checked for a leaking float and thought I could feel something in it. I unsoldered the little plug on the float and gas ran out. Had to replace the float as couldn't find where the gas was getting in.

Bedard - purchase/install an inline fuel shutoff valve - and use it - even after carb fixed.

that raw gas will get into your crankcase oil - diluted oil will not adequately lube engine - short engine life.