Ornery;
Hey.
Well first off, while I have a sound mechanical knowledge of small engines, I'm not awefully experienced in servicing every type of them. I'm more into antique small engines, primarily Briggs. Let's try and nail your problem down, though. It is considerably harder to troubleshoot in text than it is to actually be there and hear the engine run.
Starting with your carb problem. Does it still flood with gasoline? Definately not normal.
You need to check and make sure the float is operating properly. It needs to be setup just right, so when the float bowl fills with fuel, the needle seals off the inlet. I suggest you re-build it, as it could be the source of all your problems.
After you put the rebuild kit on, before you put the carb back together, turn it upside down so the float is sealing against the inlet seat. Adjust the tang that controls the float needle so that the float is level when its sealed. Remember to make this adjustment with the carb upside down.
If it has an automatic choke, make sure it's not sticking closed or partially closed.
You should also check to make sure the fuel/air mixture is adjusted properly. You can do this anytime with your engine, but obviously you have to do it after you rebuild it.
I don't know offhand the rough adjustments for your model, but try something like 1/2 - 1 turn out on the idle mixture screw, and 1 1/4 - 1 3/4 out on the highspeed mixture screw. I think that should get the engine started. In any case, once you get it started, you should proceed to fine tune the mixture. With the engine idling, slowly turn the idle mixture screw out. When you reach a certain point, you will hear the engine start to sputter and miss. This is called a rich-roll. Stop, and start turning the screw in. Again, the engine will start sputtering. This is called a lean-roll. Turn the screw back to the middle point between these two conditions, it's usually optimal.
Do the same thing for the high speed mixture screw, but remember to have the engine under at least partial load when you do this.
As for the throttle shaft leaking air, yeah. They get worn out. There is bushings you can get to fix it, but I'd say it's not worth it unless you both have the tools to do it, and like doing that sort of work. Your O-rings will probably work fine, although probably not a long term solution.
The valves are a little trickier, and generally aren't servicable by a do-it-yourselfer unless you have the proper(and expensive) tools, other than the simple lap job. If rebuilding the carb doesen't fix (all of) your problems, I'd take it in and have them give it a valve job for you. You should probably also tell them about your little tappet griding experiment, so they could remove those shims.
Feel free to ask any questions you have. It would be better to take the wrench to your engine having an idea of what the problem is, and what you need to accomplish first, rather than just tinkering. Although that's fun too!
Anyway, Yeah, I like them. I'm more into the antique engines, though. For some reason new engines just don't appeal to me. They don't look cool, they don't sound cool, and they're much too complex. Whatever happened to the good old days?!
Here are some pictures of a few engines I have bought off of flea-bay in the last couple of months.
Briggs Model WI #1
Briggs Model WI #2
Briggs Model WI #3
Briggs Model WI #4
Briggs Model WI #5
Nice briggs Model WI, Type 301101, Serial# 1074316. A latter version, made in February or March of 1949. Should make an excellent restoration project.
Briggs Model NP #1
Briggs Model NP #2
Briggs Model NP #3
Briggs Model NP #4
Briggs Model NP #5
Neglected, but seemingly complete Briggs Model NP, Type# 306598, Serial# 1438659. Another late version of an engine, made in September 1951. Gives me a good excuse to buy a bead-blaster.
Briggs Model Y #1
Briggs Model Y #2
Briggs Model Y #3
Briggs Model Y #4
Briggs Model Y in restored condition, supposedly manufactured 1935. Still haven't gotten it to confirm.
Briggs Model Unknown#1
Briggs Model Unknown #2
Haven't recieved this one yet, either. My best guess is some form of a model N engine, maybe an early version. I like surprises.
Briggs Model 6s
Nothing spectacular about this engine, just thought i'd pick it up. Looks to be in decent condition, and complete. Will be fun to restore. Has a cool old sparkplug in it.
ttyl,