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My craftsman 6.75 Gold mower will only run on choke.
Background: The first symptoms were a very slow revving (chugging) engine that would take about 3-4 minutes to come off choke and then run well. First thing I did was to remove and clean the carb and reinstall. No change. Next, I replaced the float and seat, but there are numerous carb versions, and the needle and seat I got were not compatible with my carb. I also realized that a new carb cost the same as the needle and seat, so I ordered a new carb. Put it on, and PRESTO! First pull, the mower fired right up and ran beautifully. I mowed my front and back lawns, and parked the mower back in the garage. The next weekend I went to mow the lawns again, and the mower won't start. I can get it to run for about two seconds by spraying fuel starter into the carb. I removed the float bowl; fuel with no debris in the bowl, float and needle work as expected. Fuel from the tank flows freely. Auto Choke linkage is correct (I also replaced the auto choke spring). Throttle linkage is working as expected. Idle speed is OK. There are no unusual noises heard when the engine is running. No vacuum leaks. New fuel.

I can keep the engine running by holding the choke closed. Even after close to ten minutes, if I let the choke open, the mower dies.
Any suggestions about what to do next?

That's a sign of starving for fuel when you have to choke it to run, go back through the fuel supply starting with the tank vent

Good thought. Even though I get unrestricted flow from the tank to the carb...I removed the tank and thoroughly cleaned it and the cap. Insured that the vent in the cap is clear and passes air. Confirmed no kinks or restrictions in the fuel line.

Removed Carb (again). This is a new carb, less than 20 minutes run time. Checked the main jet orifices, all clear. All ports flow air. Checked float, float seat and float valve all are clean and show no wear. Fuel in bowl is clean. Pulled plug, nice color with good gap. Verified that the accelerator and choke linkage is correct.

When I use starter fluid, the engine will run for about 2-3 seconds then acts like it runs out of fuel. Without starter fluid, it will not fire.

I have spent more time than this is worth. Unless someone has another suggestion, I'm off to the hardware store to buy a new mower. This is ridiculous.

Did you check to see if the fuel supply line isn’t kinked or clogged? Don’t take this wrong, because I have done it myself, but did you forget to open the fuel valve after shutting it down last week after mowing? Fuel filter clogged?

Oddjob said:

Did you check to see if the fuel supply line isn’t kinked or clogged? Don’t take this wrong, because I have done it myself, but did you forget to open the fuel valve after shutting it down last week after mowing? Fuel filter clogged?

Click to expand...

Yes. Fuel flows freely from the tank to the carb. Tank vent is clear. Hose is not kinked or restricted. No fuel valve or fuel filter in this application. Main jet is clear.

Additional steps I've taken:
Spark plug removed and confirmed proper gap.
Head bolts retorqued.
Confirmed carb to intake tube is sealed.
Removing fuel cap has no effect.

Next to look at:
insure crankshaft key is not sheared (unlikely since went I get it to run on choke, it runs good)
Tear into the engine and inspect the cam. I understand the cam and drive gear is plastic and can slip on the shaft.

acat said:

Yes. Fuel flows freely from the tank to the carb. Tank vent is clear. Hose is not kinked or restricted. No fuel valve or fuel filter in this application. Main jet is clear.

Additional steps I've taken:
Spark plug removed and confirmed proper gap.
Head bolts retorqued.
Confirmed carb to intake tube is sealed.
Removing fuel cap has no effect.

Next to look at:
insure crankshaft key is not sheared (unlikely since went I get it to run on choke, it runs good)
Tear into the engine and inspect the cam. I understand the cam and drive gear is plastic and can slip on the shaft.

Click to expand...

So after replacing the original carburetor with aftermarket carburetor and it still isn’t running right, what does that tell you? The aftermarket carburetor isn’t working right if you have to hold choke closed. Plan C, try another carburetor.