Mid-2000s Troy-Bilt Tiller cutting off

[OldSchoolSC]

Greetings all. This past weekend I pulled my old Troy-Bilt Tuffy tiller out of the shed, where it's been stored for some 4 years without being started. Purged all the old fuel and replaced with new non-ethanol. The carb assembly isn't the traditional type with the bowl, float, etc. It's a very small, simple linear unit that is mounted directly on top of the gas tank and has a fuel pickup tube that dips down into the tank. I took it all apart and sprayed it out with carb spray, and put it all back together. Finally got it to start yesterday by priming the 'carb'/butterfly valve assy with gas, but it would only run for about 10 seconds and then die. I finally gave up and called it a day. Went out today, primed the carb and it fired right up and ran for a long time, but ran a bit rough, with the rpm's cycling up and down a bit. After about 15 minutes of tilling, it began cutting off without warning. It would only restart after priming again, and only run for a minute or so. It acts like the fuel is simply being cut off...like its losing it's prime.

I feel like the problem is in the carb assembly. There doesn't really seem to be much to rebuild as far as I can tell, so I'm thinking about taking it back off and soaking it for a while. My knowledge about these is cursory at best, so I'm looking to y'all for suggestions. Sticker on front of engine says it's a 4.0 HP, but other references say it's a 3.75 HP.

Thanks in advance for any input!

 

[ILENGINE]

Two things. The screen on the short pickup tube and or adjustment valve has picked up some residual crap from the old fuel, or the fuel pump diaphragm isn't working well enough to keep the fuel pumped up into the little well under the short fuel pickup tube.

 

[Fish]

Likely just a layer of water and crud in the gas tank, especially the little bowl cup under the carb. Over time with water sitting there, it can rust out and start leaking.
Here is a pic of the tank without the carb.

 

[OldSchoolSC]

Thanks folks! I took the carb back apart and sprayed it out with carb spray, letting it soak for a couple of hours. Also found a replacement diaphram/gasket/spring at my local True Value and replaced the old. Cleaned the tank and bowl as best as I could, but it's still pretty rusty in there. Put it back together after priming the little bowl in the tank. Started on the first pull and purred like a kitten when on full or near full choke. Didn't run well at any other choke setting, even when warm. Seems to like a richer mix to run smoothly.

Now for the hard part...gotta bust some sod.

Thank you again for your input. This was a learning experience for me!

 

[Fish]

Did you adjust the mixture screw?

 

[OldSchoolSC]

I adjusted the screw circled in this pic back when it was cutting off, but it didn't make any difference. Haven't tried it since it's been running better, but I will try. Thank you!

 

[OldSchoolSC]

Well, it seems that I'm not out of the woods yet. Tiller wouldn't start on its own today, had to spray starting fluid into carb. THEN she started on 1st pull, but only idled somewhat smoothly, again seeming to prefer nearly full choke. Tinkered with the adjustment screw mentioned above, and it did not like that. Still managed to get it to idle so-so, and tried actually tilling with it. Got about 10 feet and it died. Starts back now only with carb spray or gas to prime, then cuts off after a couple of seconds.

Help!