I have a 35 hp gd that seems to be haunted About 2 months ago I replaced the fuel lines, gas tank, plugs, air filter, gas filter and had the carb cleaned. I had let gas sit too long (stupid!) and it had detiorated the fuel lines, fowling up the carb jets. Now, after running on the water for about 10 minutes at 3000 rpm it will sputter and act like it will quit. I have had to put back to the ramp at about 1200 rpm. I have checked all the fittings several times and have tried unscrewing the gas cap thinking it is a venting issue. Doesn't help. The bulb seems soft and I have to keep squeezing it to keep the rpms higher than 1200. I replaced the bulb with a Suzuki bulb when I replaced the gas lines. Any ideas?

Fuel pump went out.

Sounds like an air leak in your fuel line to me. Any quick connects? Have you tried running it without the inline primer bulb hooked up?
Also, unhook your hose from the fuel pump going to the carb and crank the engine to see if it pushes fuel through it. Could be bad fuel pump.

Make sure the carb and jets in the carb are thoroughly cleaned.
Make sure you are getting good spark to both cylinders. Make sure the plug wires aren't arcing causing your low rpms.

Make sure you have fresh gas, and also make sure you don't have gas in your oil.

Just a few things I would check before digging more into it.

Pretty simple, really. Air, spark, fuel.

aaaaaaaaaaaaaannnnnnnnnddddd, Russ beat me to it in 4 words

Wow!!! Thanks guys. I will try all the above this evening after work. I do have a quick disconnect on the fuel line/gas tank and it does seem very wiggly to me. I think I will take it off and use a barb instead. I thought about the fuel pump, but why would it work good for about 10 minutes and then start sputtering. Wouldn't the fuel pump just not pump fuel adequately from the start?

Not necessarily. Depends on when it goes out. I've personally witnessed a cam driven pump work then not work, then work, then not work. Finally quit pumping enough to even keep it running
The vacuum pumps will just quit working eventually.