6461 Commercial LB won't stay running

[CLB6461]

So my commercial lawnboy model 6461 Was brought out of moth balls recently. I like to do the work myself, find it relaxing. Spark plug was out and wd-40 was sprayed in cylinder as it sat. Fuel system was drained and cleaned also prior to it's storage. So I put it back together. Added fresh gas mixture, new plug, said prayer and it started. Not first pull but it started.
Cut some grass, 2 yards maybe 75"x100" each. Mower cut well but after these lawns mower started stalling. I start it on full ckoke, 1 pull, mower starts, I take choke off it runs at full speed for 60-90 seconds then stalls. Choking it to keep it running dos'nt work it just fouls out plug. Any Ideas?
PS Where should the altitude adjustment screw be. If you can't adjust it with motor running (because motot won't stay running) what is a good starting piont before adjusting it? After turning it all the way in [clockwise] 1 turn out or 1 1/2 turns out?

 

[chance123]

Your machine is obviously starving for fuel. Try loosening your fuel cap when it starts to die. Many times the LB fuel cap vent is plugged and won't allow air to enter the fuel tank. This is just like holding your finger over a straw full of liquid. remove your finger, air goes in, and the liquid drains. If that doesn't help, drop your float bowl and clean the main jet with a tag wire and carb spray.

 

[CLB6461]

So my commercial lawnboy model 6461 Was brought out of moth balls recently. I like to do the work myself, find it relaxing. Spark plug was out and wd-40 was sprayed in cylinder as it sat. Fuel system was drained and cleaned also prior to it's storage. So I put it back together. Added fresh gas mixture, new plug, said prayer and it started. Not first pull but it started.
Cut some grass, 2 yards maybe 75"x100" each. Mower cut well but after these lawns mower started stalling. I start it on full ckoke, 1 pull, mower starts, I take choke off it runs at full speed for 60-90 seconds then stalls. Choking it to keep it running dos'nt work it just fouls out plug. Any Ideas?
PS Where should the altitude adjustment screw be. If you can't adjust it with motor running (because motot won't stay running) what is a good starting piont before adjusting it? After turning it all the way in [clockwise] 1 turn out or 1 1/2 turns out?

Thanks chance123. That was my next step, clean fuel jet. There was a little bit of corrosion; sediment in the bowl, so cleaning the jet may do it. Can you tell me where to set the altitude screw from scratch. I have it at 1/12 turns out.

 

[Phototone]

Initial setting is 2 turns out. But, why should that adjustment change over the winter?