Snowblower issues

[BrianG]

OK, it's supposed to snow a decent amount tomorrow and my snowblower is acting stupid. First a little background:

It's a Simplicity snowblower with an 8HP Tecumseh engine. It was running fine last year until it just died on me. After inspecting it, I found gas leaking from a hole. Something must have worked loose and fell out, so I plugged it with a 4mm screw from my r/c box and it seemed to run fine after that for the rest of the year (about 3-4 more uses).

So, this year, I decided to fire it up and it's running like crap. Actually, it runs nice, once I can get it going, but keeping it going is a challenge (and getting it started back up).

In previous years, to start it, I followed this procedure:
When the engine is cold, I start with the choke on full, throttle about 1/2, and then use the electric start. After a couple cycles, it turns on. I let it warm up a little, then set the choke about 1/2 way and bring the throttle up to running speed (just about max). After the motor warms up a while, I turn the choke off completely. Then I'm able to do whatever I need to do. Shutting it off was just a matter of lowering the throttle and hitting the on/off switch.

This year, the cycle is a bit different:
When the engine is cold, I have to set the choke to "off", throttle almost "min", and then crank it. Setting the choke or throttle to any other position won't let it start at all (won't even "catch"). Even then, it has a hard time trying to start; it seems like it "fires" only about 25% of the time resulting in a very rough idle and more than normal smoke coming from the exhaust. Eventually, it gets to a point where it fires about 50% the time, then 75%, then will idle somewhat decently and I can increase the throttle to running speed. But since the choke is already on full "off", it starts to get rougher as the engine warms up. I can get one pass of the driveway done before it starts backfiring, running rough, then it stalls, and then I have a heck of a time getting it working again. It's faster for me just to shovel the stupid driveway. Also, when I can get it running ok, shutting it off is odd too. I lower the throttle, flick the on/off switch and it continues to run for about 20 seconds.

Nothing happened between last year and this year, so I don't know what's up. Fuel delivery seems good because I've gone through a tank and a half between trying to start it and accomplishing what I can with the driveway. The only oddity is that screw hack job I did last year, but it ran fine several times after that, so I don't know what's up. I don't even know what that area does. So, I included a couple of pics. The first one just shows the muffler, choke, throttle, and on/off switch. The second pic (sorry about the blur), is the area underneath the muffler and shows where I put that screw in.





Can anyone give me a hint of what could be going on? The small engine shop said to bring it in, but there's no way I'll be able to fit it in my little hatchback. And I don't know of anyone who does house calls...

I'd really like to know what that screw is supposed to be and if that's the cause of my problems...