2003 40hp 2-stroke yamaha smoking alot at idle speed

gblase

Recruit
Joined
Mar 17, 2011
Messages
1
i have this motor on a 17' 52" bottom flat boat, set up to bowfish, it smokes a tremendous amount while at idle. starts easy, picks boat up on plane in a sec with no bog when you crack throttle. acts like the fuel oil mixture is twice as much as it needs. i have called yamaha and verified the motor being a 50/1 ratio. i have the gas mixed correctly. it has a "fuel enrichment " red lever on side of motor that i have never seen before but i have tried the boat in the "normal" setting and in the "closed" setting and have not noticed a change in the amount of smoke
i have had several 2 stroke outboards but none have ever smoked this bad and run out this good, i would appreciate it if anyone has had this problem and knows a solution.
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: 2003 40hp 2-stroke yamaha smoking alot at idle speed

If your fuel pump diaphragm is cracked it will suck excess raw fuel into that cylinder creating a rich condition and smoke. Remove fuel pump but leave hoses connected, pump primer bulb and check for fuel coming out the back of pump. Check the spark plug on the cylinder that runs the pump for wet/fuel fowling. Pump is about $50 on-line and dead easy to replace. Lever enrichment lever should stay in the normal position. Is your gas/oil mixture pretty fresh, not too old? I run a 90HP Yamaha premix and I get less smoke with 100% Synthetic Outboard Oil like Pennzoil or Quicksilver.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
Re: 2003 40hp 2-stroke yamaha smoking alot at idle speed

There are 3 settings on that red lever, normal, open, and closed. Just in case you did not see that.
Fuel pump diaphragm is one and the diaphragm in the prime start system need to be looked at also.
seeing how you have not posted a motor model # and said you mixed the fuel I assume the motor does not have oil injection.
may be time to de carbon the motor
 
Top