merc 15hp running poor

[imported_Vince]

This one is a long one. This engine is a 1990 vintage Merc 15HP (ser #ODO72721). The motor has great startup; great idle, but dies when full throttle is given in gear. Let me tell you what I have done up to this point. Replaced the fuel tank and hoses, spark plugs, fuel filter, and removed and installed repair kit to the carb (wmc-28). Note repair kit is a gasket and spring kit no needle valves were replaced. All of this did not change the operation of the motor in anyway. I thing I can tell you is that if you open the throttle and pull out on the choke you can get the motor to go. Note that you do not need to pull the choke to the point were it pumps the prime button. What do I do next?

 

[tashasdaddy]

Re: merc 15hp running poor

did you clean the carb and needle valves before reassembling. have you adjusted the needle valves. must ne done with the motor in the water as out of water there is no back pressure on the exhaust.

 

[imported_Vince]

Re: merc 15hp running poor

I did clean the carb parts with solvent and reassembled. I believe that the high speed jet is fixed and the low speed needle is adjustable. I did run the motor and adjust the low speed needle. It did not help. Return it to 2 turn out.

 

[tashasdaddy]

Re: merc 15hp running poor

try pumping the bulb when throttling up, if it works points to fuel pump or you didn't get high speed jets clean, may have to run small wire thru the orifice. also there is a procedure called 'linc n sinc' don't know what it is for your motor, but it puts the carbs in sinc with the engine timing.(advance)

 

[ozziebob]

Re: merc 15hp running poor

It interests me that if you pull on the fast idle choke lever it accelerates fine even though the primer is not being activated. As this is not enrichening the fuel mixture may be you do not have a carby fault at all?? This lever on a number of models has a wire that is directly linked to the spark advance lever. By pulling this you may be advancing the timming giving it the ability to accelerate. Check your timing at wot. If you are unsure how write me back. Also as a quick check without running engine open throttle and see if ball joint just under flywheel R.H.S moves with the throttle (looking from front of motor)

 

[tashasdaddy]

Re: merc 15hp running poor

agree with ozzie. what he is talking about is when you did the carbs you threw the linc and sinc out, this sincs the timing and carbs so they advance together properly.

 

[imported_Vince]

Re: merc 15hp running poor

Ok Ozzie Tell me how to check the timing at wot, and how do I check and /or correct this thing you called link and sinc. Im ready to try anything to make this motor work.

 

[tashasdaddy]

Re: merc 15hp running poor

i don't have the manual for your motor so i don't want to tell you a wrong procedure