The most common causes for this are a float that is saturated or not set level / a leaking inlet valve or seat defect. When you install the inlet needle, you may note that some have the little retaining wire that seems to direct itself out a tad sideways. If that is the case- install it away from the housing to prevent binding. If this has a fuel tank under the hood, it is also possible for the fuel to come in through a defect or mis-assembled pump as well.

Buy a can of spray carburetor cleaner. With the air filter cover off, spray about a one or two second burst of the carb cleaner into the carburetor throat. Then try to start the engine. If the engine starts and runs for about 2 seconds each time you spray the cleaner into the carb throat....your no start issue is due to no fuel delivery from the carb to the intake. If, however...the carb cleaner does not provoke the engine to run (for a couple seconds) that means the problem lies elsewhere. Bear in mind, the mere presence of a spark does not mean the spark is happening at the proper time. It is possible that the first episode of trouble, resulting in some "back firing" may have partially sheared the flywheel key, which would put the ignition spark timing to something other than the proper time. But don't go yanking the flywheel off yet. Let's see how it does on the alternate fuel (carb cleaner) first. Then we'll go from there to a next step.

A few updates... Mistakenly listed my model number as "31H777" when it is actually a "31P777." After reaching point of experiencing symptoms, I checked and didn't notice the choke butterfly being stuck in a closed position. I moved the throttle lever back and forth, but there was no improvement to the conditions. I received Walt's detailed instructions for checking and adjusting the valves, as well as some of the other troubleshooting suggestions. Here are my findings: 1.) I tried the test in the last paragraph (which was to look for an additional little movement on the intake valve, just after it was all the way in, which would verify the compression release), but didn't notice any additional movement towards fully closed. 2.) I followed the instructions for checking and adjusting the valves. The intake valve did need adjusted, so I made the appropriate adjustment. I also tightened a bolt that was a little loose on the rocker arm for the intake valve. 3.) I checked to see if I had spark (with the spark plug removed); that checked out fine. 4.) I turned the engine in the direction of operation (hand on the screen) before I started mowing (i.e. before any symptoms are observed). It was a little tight at one point (which I believe is right when I was getting to TDC, since I also noticed it when I was adjusting the valves). I then did the same test after mowing and experiencing problems... this time, there was a groaning kind of sound at one point (on every revolution). It sounded like something was "tight" and/or rubbing. Could it be compression or compression release related? So, based on the additional information contained in Number 4 above, what do you suggest I do next? Thanks. Tim

***"Anyone?"*** Where shall I begin?? ***"Basically, my question is, are these two carb interchangable? I'm guessing the answer is "no" and that is what my engine wasn't running right."*** Well, as an "off the shelf, ready-to-go" component that is EPA compliant, that auction bought carb "might not" be right for your engine, but if that carb was functional (not defective), it should still operate on your engine without drowning the engine with fuel. If the float, needle and seat are working right, no fuel will flow when the engine is not running. And if the carb main jet is in place, and of anything close to the appropriate orifice diameter (jet size), the engine should run and restart after shut down. So, have you inspected the "auction bought carb" to see if it has all its guts still in place? At this point in the history of ICEs, carburetor size can pretty well be calculated by an engineer sitting in front of a computer. There is such a large data base to invoke (well over 100 years and counting) that hardly anything needs to be "re-invented" and so a carburetor can be selected from a big list of existing designs without having to do the "trial and error" method in such a big way. Of course, after choosing a carb for an engine, the engine will be tested under laboratory conditions to make certain that it operates well enough to go to market, and is compliant with EPA and other "standards". What does all the preceding have to do with the problem outlined in this thread?? Well, let's go a bit further down the information pathway. Many engine OEMs will use identical "base engines" in various different Horsepower output ratings, with only some minor changes of carburation. Sometimes the changes are nothing but a different jet size, but sometimes the difference will include a larger, or smaller, throat size in conjunction with diffent size jets. Now all that was just to sort of explain how marketing pressures and other concerns (like EPA standards) can affect which carb might be used on a given engine, but basically, a range of carbs can be used on various different engines in a "type and displacement group" and still be functional. You are trying to use a carburetor of unknown origin and condition and have not gotten satisfactory results. That does not prove that the carb is unusable on this engine, but it might prove that this particular carb is defective. I have basically the same engine as you (mine is 422707-0166-01) in a TSC Huskee. I will post some pictures of MY carb and we'll compare. ***"I should also mention that carb rebuild kits for this carb made by stens, Oregon, and Briggs no longer come with high speed needles/screws anymore. I had to buy one separately to replace the one on the old carb."*** I don't know if you wanted commentary on that or not, but here goes. Because the adjustable main jet needle valve carbs are destined to fade into history, I would guess that the carb OEMs have decided not to furnish that needle valve with the gasket set any longer. Much better marketing strategy for them to just have a gasket set that fits ALL carbs of that series type than to toss in an unused needle too. This allows them to save a bundle on their end by not making a needle for every kit. And you can bet that any reduction in price of the kit without the needle can be measured in pennies on the consumer side, but in dollars on the manufacturer's side. And then, they can sell any needles at a premium price because applications calling for that part have placed it in a "niche market" instead of a "mass market". Bottom line summary to this book of mine is: "If the auction bought carb is functional, it should not drown the engine like you describe. Also, if you believe this engine has a defective head gasket, you should address and correct that problem before attempting to do anything with the induction system. I'll get some pics.