Engine runs on half choke

It's too lean; not enough fuel mixed with the air. Look for the main mixture screw--it should be a large screw with a spring under it on the carburetor. Run the engine until it's warm.

With the engine running, turn the screw outward (lefty-loosey) about 1/8 turn slowly and see if it improves. Slowly turn the screw back and forth until it runs best with the choke completely off. Then set it 1/8 turn richer (turn screw outward 1/8 turn) than the best position.

Reason for doing this: Conditions change, even the barometric pressure. Small engines run okay if they are a little rich but not if they are a little lean.

Many times with a gas mix, after sitting for a while, the mix separates and gums up the carb. Taking the carb off and soaking it overnight in a parts or carb cleaner and running carb cleaner through the tank and gas lines will cure this.

dirt or water in carburetor.Choke helps suck more gas in engine to run better.

Use the diagnostic sheet attached to help determine the problem.

The choke system is connected to the half throttle position, if you lift the throttle trigger the choke pull will automatically return, whilst trying to start do not lift the throttle trigger, the starting procedure is, pump the primer bulb as many times as it takes to 3/4 fill the bulb, pull the choke pull fully out, this will switch the saw on and engage the half throttle, crank the engine until it fires once, do not continue to pull,it will actually not run on full choke, if you do continue to crank with the choke fully out, you will very quickly flood the engine, now push the choke fully in, now crank the engine until it fires up, lift the throttle trigger once, this will dissengage the half throttle, and it should now come down to idle.

I would suggest a new plug and fresh gas and oil mix.push the primer bulb 8-10 times and turn choke to full.pull cord about 4 or 5 times until it starts.if it don,t stay running turn choke to half and pull cord until starts should stay running.let run for about 10 seconds then turn off choke.Almost forgot that during this whole process you hold throttle wide open.

Zama Carburetor:
http://www.zamacarb.com/tipspage.html
Walbro Carburetor:
http://tech.flygsw.org/walbro_tuneup.htm

Sounds like it needs a fuel pump kit, and possibly also a carby kit.

take photos as you are pulling the fuel pump or carby apart, or get a service manual for the outboard. The dealer might photocopy the pages you need if you ask nicely.

Start your adjustment by turning both screws (gas and air) all the way in and then back them out one and a fourth turn. Start from there. Hope this helps.

You need to disassemble the carb. and spray with carb. cleaner. If you need tips on how to do this, just let me know. You may need a new carb. kit as well, but we won't know that until you first perform the first step, or if the carb. parts are more than 3 years old. If they are, then go ahead and buy the carb. kit and replace the parts.

Jim