So your carb has the jet adjust on the front of the carb?
If so that screw is for slow idle smooth engine idle adjust. I've seen some that just 1/4 turn difference CW-CCW will produce non-smooth idle and some will need just a slight different adjust from cold engine to warm engine. I usually go for the smoothest warm engine setting. Briggs says to start around 1 1/2 turns out but I've seen some want to be correct at just 1/2 turn out.
Some of them carb that do not have a low jet adjust and just will not be real smooth at idle. I prefer the type carbs that can be adjusted.
Also YOU WILL find that sometimes the engine will be running smooth for long period of time and eventually start running little bit rough and keep getting worse. Instead of pulling the carb off, Just let the engine cool and remove the bowl drain bolt and drain the carb bowl and SURPRISE 90% of time it will then run smooth. Do not drain the bowl when the engine is hot because the gas spills direct onto the hot muffler. (might have to prime the carb throat afterwards to get quick start up)
Quite often I've cleared up a rough run also on the opposed twin carbs without removing the carb from the manifold. Take the 4 screws out of the top and the gasket will need to come up with the top because the float is under the gasket. I can usually be careful and use a putty knife and work the gasket loose from the bottom section of the carb and quite often the gasket will remain good.
If the gasket breaks just replace and be sure you use the correct one of the several from a kit and lube the gasket when going back with vaseline on both sides.
After removing the top on a rough runner just use low pressure air 20# or so and blow air across the top of the carb or use canned carb cleaned into the jet holes. Do not direct inject air compressor air, just wave the nozzle across the top of the carb jet area, re-install the top and test. If you have the carb off the manifold be sure and use a gasket on EACH SIDE of the plastic spacer below the carb to manifold.
If your does not straighten up just install another carb and re-test.
Next:. HEADS UP CAUTION
Be sure you get them 3 screws that hold the breather pan to the carb body good and snug. They will vibrate loose and go inside the engine. I use a blue locktite threadlocker on them just enough that they won't back out due to vibs.
That engine uses champion RJ19LM spark plugs or equal.
If it gets hard to start when hot replace the plugs and if that don't get a go replace the magneto and set the air gap at .010. I get good operation from the $20 magnetos, just be sure it's not installed upside down, some are labeled up in small letters, some not labeled.
Them type carbs are user friendly to work on and usually very reliable until they get a small slug of water inside.
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OK WILL try some of those recommendations!
I have several magnetos they all work
I have two Nikki carbs 4 screw don't like them as much!
My 3 screw carb was on the machine
It came with it with fuel adjustment screw under front of carb i think I have a better chance with that one for adjustment!
