Small Engines (Lawn Mowers, etc.): Snowblower runs choke half open only!, valve spring compressor, compression stroke

Question
So i bought a used snowblower 1982 Toro 724(more importantly a Tecumseh h70-130176f.  Anyway the machine starts up gr8, and for the first couple snows, big ones at that, the machine ran pretty well.  at idle the machine would kinda sputter and make small pops, but when i engaged the auger and hit the snow it seemed to run fine!

bout 2 weeks ago i ran it in some slushy, heavy snow, i noticed the machine would run about 20ft and start to lose power, the engine would slow and it just died.  I hoped it was the slush.  So i put in a new plug according to specs, and thought maybe it would perform better the next normal snow.  That was yesterday, and the machine was doing the same thing.  This time i paused to play around with the machine.  

So at idle with the choke closed, and throttle up the machine is running very heavy, spitting and small backfires.  If i power on the auger here it may run for a bit but won't take a load without dying.  

Then when i messed around with the choke, and where i found it runs the best is at halfway open.  I can pretty much get the machine to run clean, and finish the job at hand.

Am i harming my machine by running with the choke open like that? Does my problem lie within the carb?  and if so how tough is that to get to, and take care of? My concern is that this may just progress to where it doesn't run at all, so instead of running it like this i would like to get to the root of the problem.  Any suggestions?

Thanks

Answer
Hello Chris:

From your Description of the Backfiring and the Choke Required to be Half Closed, it Sounds like the Valves May Require Resetting and Reseating. You will Need a Small Engine Valve Spring Compressor for this Repair. To Set the Proper Clearance of the Valves on this Mower you have to Lightly Grind the Valve Stem Tip and Check the Clearance Between the Valve Stem Tip and the Tappet with the Engine Set at TDC on the Compression Stroke. You will have to Remove the Cylinder Head, Carburetor and the Crankcase Breather to Access the Valves, Valve Springs and Keepers. You Grind a Small Amount and Then Install the Valve Back Into the Block, Hold the Valve Seated by Hand and Check the Clearance. Do this Until the Clearance is .004in - .006in Intake and .008in - .009in Exhaust. An Automotive Valve Grinder is Mainly Used for the Valve Seats and Faces. If the Valve Requires Refacing, then the Valve Grinder can be Used. If the Valve Face is Good, then Simply Grinding the Stem is All that is Required. You can View a Breakdown/IPL of the Mower at this Site Addy, https://lookup3.toro.com/partdex/default.cfm and Select Start Parts Viewer. Now Enter the Model Numbers. Now Select View Assembly Drawings. You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.outdoordistributors.com/ and Select the T. Then Select Tecumseh. Then Select Don't have Part Numbers. Then Enter the Model Numbers. Then Select your Model and Download the File for Online Viewing. After Looking at the Breakdown, if you Decide you want to Attempt this Repair, then Let me know and I will Supply Detailed Instructions and Assist you with Any More Questions you May have. If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Thanks.

Respectfully

John