Suzuki Dt 150 running like crap

I recently bought a 1996 Dt 150. I put it on my boat. And with the muffs on or in a barrel, it sounds awesome. But when I put it in the water and put it in gear, it instantly goes to running like crap. Giving it gas makes no difference. It won't even attempt to get on plane. I have never owned a Suzuki and don't know where to start??? Also, every time I crank it, and while it's running, an alarm is going off. It's a 3 steady long beeps. A long pause. And 3 more longs beeps. Hoping someone can tell me what this is???

3-3 Neutral safety switch. No mention of a 3-0 code. If the switch has failed then the engine shouldn’t start is my understanding. It’s an on/off switch so I’m not sure if that’s your issue but it’s worth investigating. Switch in located on the clutch lever holder, in neutral volts should be 12V, in forward and reverse volts should be 0. Somehow it’s tied into the shift position sensor, also in the same area. The above information comes from my 2009 DF90A (four stroke). I’m learning this electrical stuff and how its all related so I’m not the best source of information. The link below will get you a pdf service manual. I bought my service manual from this outfit and didn’t get any unauthorized charges on my Visa.
Throttle Position Sensor is a 2-1 code, are you sure it’s a 3 long and not 2 long, brief pause then 1 long?
Boats.net host a Suzuki forum with very knowledgeable people.

https://www.selffixer.com/outboard.motors/suzuki/suzuki.75-225.2-stroke.1992-1999.shop.manual.htm

4 strk codes won't help you on a 2 strk carb motor. You need a manual for that motor they have oil flow warnings, and low oil warning, and overheat warning.

So I've narrowed it down to the throttle position sensor on the side of the carbs. Anyone know how to check the electrical component to verify whether it's bad or not

From a 2009 DF90A Service Manual. Values might be different since different engines but it will give you some insight. I would suggest you get a Genuine Suzuki Service Manual, they can be found on the internet for less than $20(pdf) The older the engine the cheaper they are.

https://www.selffixer.com/outboard.motors/suzuki/suzuki.75-225.2-stroke.1992-1999.shop.manual.htm

$11.95 well worth the money. I’ve purchased a few manuals from this place and so far no funky charges to the MasterCard.

Great info, thanks William. For rheostats and other components similar to TPS units, fuel gauges, etc....I fall back on my analog meters with a needle. It's much quicker to spot a "burp". I have a $100 DVA analog multimeter that is my "go to" diagnostic tool. Has been working fine for 17 years.

Here’s mine, about 40 years old. I had a friend add an external fuse since I kept blowing the internal one. User error.

Ha! She's a beauty? RCA is top notch. What ya do for DVA testing? It's really quite remarkable what you can accomplish with a good meter and a little knowledge. So you got messed up with power getting into Ohms side? As a kid I burned up a couple, Dad got really pissed, nearly got banned from his repair shop. We had a coin machine business 40's 50's 60's. I still have a 1957 Gottlieb Royal Flush Pinball machine. 100% mechanically operated. Probably worth several thousand bucks. Really cool.