Lawnmower carb issue - what else can I try?
 

I bought a Craftsman lawnmower with a 6.5 HP Tecumseh engine from Goodwill. I almost have it running, but can't get past a carb issue.

I've taken the carb apart and sprayed carb cleaner in/through everything, but for some reason it's not running. Gas runs freely from the tank through the fuel line, the float bowl (with new float) fills up fine, and it runs for 3-4 seconds with a shot of carb cleaner sprayed into the carburetor. The primer bulb is dry, but intact.

What else can I try?

What's the float bowl level? You might try raising the float a bit by bending the tab that works the needle valve.

Pull the jet(s) out located inside the float bowl and check for dirt.

Sounds like the main jet is clogged up. You can try running a thin wire thru it, after you take the carb apart. pretty common problem, especially is has been sitting for a long time.

Yep...you do NOT want to leave old gas in the carb all winter...

Your main jet is plugged. Unscrew it and hold it up to the light. In the past, I have opened the main jet to the next drill bit size using numbered bits, not ones measured in fractions. The mowers always ran better a tad rich. Of course, I live at sea level in a warm climate.

Trying to remember the old float level trick I used on Tecumseh carbs...don't hold me to it, but IIRC, a 5/16" drill bit should just fit between the top of the float and the flange the bowl fits into. A handy feeler gauge. Damn, I did it hundreds of times when I sold/worked on Toro mowers...but that was decades ago, and damned if I can remember the drill bit size. I agree with Milt & Vinman here...check that main jet. Going richer may also be wise, if you're running gasahol in your area. Alcohol in the fuel demands richer mix...

+1 Bingo! Very common problem and neat fix.

I just went through this. We had a lawn service for the last 5 yrs. Since I got laid off, well I have no excuse not to, not to mention the money savings....anyway.

I took the carb apart....then I got a can of parts cleaner at the local parts store. I left the parts in there for about 3 hours. (No rubber, etc).

Drained the gas, changed the oil and plug.

Put it back together and presto! It runs great now.

The main jet is ok. I haven't put a wire through it, but I can see light and carb cleaner ran through it. The carb really looks like it's in pretty good shape. It wasn't gummed up at all. I had hoped that the sinking float was the only problem, but I guess not. I've squirted Gumout in, around, and through everything.

The primer bulb finally split so I'm done messing with it until the replacement arrives next week. Any other ideas?

When I used the parts cleaner, parts I thought were clean had a varnish like film. It made the difference for me. Before the parts cleaner I had scrubbed and used a brush, I too could see light.

For me, it wasnt until I used the stuff. It's in a can (like a paint can) with a removable tray.

I just read about this... 11/64 is the size I saw suggested. I'll add this to my list of things to try when the new bulb arrives.

Go with the 11/64th...like I said, it was a long time ago...combine that with senior moments, and...

is the gas you're using old or new? My lawn mower is stored out doors (lame) so if I don't use it for a few weeks, the gas in it simply does not fire. New gas and it fires just fine.

It's new. The tank was dry when I picked it up. Funny thing was, on the way home from buying it I stopped at a gas station and just put gas in the mower while it was sitting in my Mazda5. The gasket was bad on the float bowl, so the gas was coming out about as fast as I put it in. Fortunately I had a big towel and was close to home.

Could be valves not seating well...is it extremely easy to pull the rope start? If that's the case you may always have to prime with a bit of gas when starting...(not enough "suck" to bring in the fuel when starting)

I've had several Lawn-Boys that ran great once they were started, but they were real buggers to start. I finally just left a propane torch in my garage. Open the torch valve (DO NOT LIGHT IT :) ) and stick it in the intake. Pull the starter and the engine will fire up. Pull the torch out and the engine will usually keep running.

At least you know you have compression and spark when it starts.

(You should always use mid-grade or premium, it will start easier. Not that that will solve this problem...)

The intake valve was stuck open when I got it. I pulled the head and freed it up. In the 4 or so seconds it's running on the shot of carb cleaner it seems to be running well. One pull and it's going.

Well, we know the problem is fuel, at least...sounds like you have all the carb problems identified...so waiting to hear good news once you get the primer bulb fixed. (edit) One additional thought...be sure the intake manifold is sealed well, not sucking air...

It's alive! I let the jet soak in some Gumout while I installed the new primer bulb. I put it all together and it started right up.