If you have ever worked on larger engines, single and dual cylinder engines are simple in design. However, they have their own quirks. Pardon if I write as if you don't know what you're doing -- I like to be as thorough as possible to help you understand my point(s).
You only need three things to run:
1. You've got spark (blue and true).
2. You've got fuel (possible flooding/rich).
3. You've got air (I'm assuming its not restricted).
Since you think it is running too rich to ignite the air/fuel mixture, I'd recommend proceeding with the following:
1. Take the air cleaner assembly off of the carburetor so you can see into air intake of the carburetor assembly. When you try starting with choke, can you see gasoline spewing out? If so, it's flooding. Does this occur without choke? If so, then it is receiving too much fuel. If not, there could be a clog in the fuel line (filter), or worse the carburetor -- you may wish to take it apart and give it a thorough cleaning/possible rebuild.
2. If you're receiving too much fuel without choke, I recommend taking note of how far the main fuel jet on the carburetor is turned out. You can achieve this by taking a flat screw driver and turning the jet clock-wise (in). Keep track of how many turns by counting half turns. Screw it in as far as it will go, but do not snug it down/turn too tight -- this could cause damage to the seat and needle. Once you have your marking (let's assume it is 2.75 turns), turn it back out to it's original setting. This will give you a point of reference so if the following does not work, you can put it back into the setting you started with -- one you know has worked in the past.
Now, turn it clock-wise, a quarter turn at a time, and try starting. Eventually, it should begin to flutter and fire right up (assuming you haven't fouled out the spark plug from flooding -- you may need to wait after each attempt for the flood to dissipate).
3. Once you have it running, there is a method of finding the carburetor's "happy place" (as I like to call it). In it's running state, let it warm up without stalling and run at full throttle. Then, take the main fuel jet and screw it in until it starts to flutter as if it wants to stall. Now, back the jet screw out until it does the same. Note how many turns there are between these two points. Smack in the middle should work fine (it did on my Wheel Horse).
4. Now, turn back the throttle to an idle position and set your idle. This screw should be on a piece that pivots on top of the carburetor. It has been my experience with Tecumseh engines that you may want to keep this turned up higher than normal, especially for cold and/or damp weather (they are temperamental, like Holley Carburetors for cars).
I hope this helps. If i have made an error, please someone else provide some input. This is my method and it "usually" works -- although I've got a stubborn Snapper that has carburetor issues.
Good luck!
