1990 Yamaha Outboard Question

#1 08-14-2006, 01:27 PM

I have a 150 Yamaha, and recently I have replaced a coil due to a dead cylinder. The syptoms were I was only getting about 4200 RPMs. Well, after I replaced the cylinder she ran like a top at 5000 RPMs. Well, right here recently she is doing the same thing. But, this past weekend I let a friend borrow the boat and he ran the tank dry. But she is displaying the same syptoms as the dead coil issue. Is it possible that I have a fuel delivery issue? I put brand new NGK plugs in her and fired her up and ran it. Well, for the first 200 yards she ran like a champ at the correct RPMs, then the same 4200 RPM running. Anybody ever dealt with this????

bigshrimpin · #2 08-14-2006, 03:03 PM

Check the plugs first . . . Read the ceramic material . . . should be paper bag brown. There are some good resources online for reading spark plugs.

If they look "ok" . . . Is the engine surging? loosen fuel pump mounting screws and squeeze the primer bulb and see if fuel is weeping out the fuel pumps. if yes replace fuel pumps.

To eliminate the carbs: Take the airbox cover off the carbs and have someone drive the boat at WOT. Look down the throat of each carb. There should be a nice fan shaped spray of fuel in each carbs - venturi. If one of the fans is significantly less than the other . . . then limp home slowly and rebuild (clean) the carbs .

reelapeelin · #3 08-15-2006, 10:09 AM

If your friend "ran it dry'', possibly something got sucked into the gas intake in the tank that normally would not have... :P...