Carb setting fouling plugs/thermostat

[Icr242005]

Hello, question about 1989 Force 50hp new to me. Compression test was 135 and 140. Bought this boat from a guy that made it his project but he became ill and did not finish. It had some lower end problems. after removing the thermostat (thought it could be bad) and replacing water pump and figuring out shift linkage (what a pain in the a.. that was) I put the boat on a lake and after 3 to 4 gallons of fuel it fouled out a set of spark plug. Changed plugs and figured it was bad gas, took it out the next day, same thing.during these runs, it was using a ton of gas. Replaced thermostat, removed carb, cleaned/soaked. Now here we go, IMO, no thermostat- motor always running to cold to seat piston/rings so that would make it run way to rich. Second part. The air screw was at 1 3/4 turns out. Book says 1 turn out. I took air screw in until it stumbled and back out 1/2 turn from there which put the screw just about one turn out. I have ran about a 1 1/4 tank of gas and has not fouled plugs but seems to me still running rich. On most, not all, but most small engine cards, if you turn air screw in it reduces the amount of air going in carb which would make it run more rich of fuel.
Question 1 would no thermostat make thing thing run so rich to foul plugs.
Question 2 Can I take the air screw in more without running it so lean to burn a hole in piston. I don't understand this carb and its air screw. Any advise/help would be greatly appreciated

 

[pnwboat]

What kind of plugs are you running?

Running the motor without a thermostat probably won't hurt anything, however, in order for the motor to run at maximum power/efficiency, the motor has to be at a certain temperature.

The air mixture screws on these carbs controls the amount of fuel mixed with the air If you turn them in, it will reduce the amount of fuel which can damage the pistons.

If you are running too rich, you may have a torn fuel pump diaphragm. There is a hose that goes from the fuel pump to a fitting on the By-Pass cover. If the diaphragm gets tear or small hole, it will suck fuel directly into the By-Pass passage which richens the mixture.

 

[Jiggz]

In addition, to PNW's suggestion, check also the choke mechanism. Make sure it stays in the full open position. And finally, unscrew the "air screw" (idle fuel air mixture screw) all the way and check make sure the pointed end is not damaged.

 

[Icr242005]

I'm running NGK BUHW. So how do you do a plug check to see how it's running (lean) without a ground strap. Thank you. Choke wide open, needle looked really good. Float was set good. It held 2 lbs of vacuume on seat for 5 mins.

 

[Jiggz]

At one turn out and the plugs not fouling you could be at the right setting. Although I still recommend setting the air screw to at least 1 1/8~ 1 1/4 turn out from slightly seated. On these motors, the plugs do always look wet and brownish and maybe conceived as rich fuel setting. In fact, if the plugs are bone dry and clean it is an indication of either too lean of a fuel setting or steam cleaning due to water intrusion into the cylinder. And yes, being two strokes, they do smoke heavily especially during idle and low speeds.