YAMAHA 40 INTERMITTANT MISFIRE PLEASE HELP!!!!!!!!!!!!!!!!!!!!

[carmron2005]

1998 tlr40hp starts fine idles ok, but when I go to plane under load it drops a cylinder momentarily. it does eventually pick back up, but it is really annoying. I have had the carbs cleaned, tried numerous sets of plugs, but the problenm still persists.

 

[Ray Neudecker]

Re: YAMAHA 40 INTERMITTANT MISFIRE PLEASE HELP!!!!!!!!!!!!!!!!!!!!

How did you determine it was dropping a cylinder? Test with a timing light. The three cylinders have had some CDI problems even though normally I would also be looking at a fuel restriction problem.

 

[carmron2005]

Re: YAMAHA 40 INTERMITTANT MISFIRE PLEASE HELP!!!!!!!!!!!!!!!!!!!!

 

[Ray Neudecker]

Re: YAMAHA 40 INTERMITTANT MISFIRE PLEASE HELP!!!!!!!!!!!!!!!!!!!!

Easiest way for me is a timing light. They can also miss fire from a lean condition. A sticking needle can also give some of these symptoms also. You could well be right about electrical on the three cylinders. Normally they will drop a cylinder when the CDI goes but can be intermittent. If the timing light shows fire to be correct while acting up, then you are back to the fuel systom.

 

[carmron2005]

Re: YAMAHA 40 INTERMITTANT MISFIRE PLEASE HELP!!!!!!!!!!!!!!!!!!!!

Originally posted by Ray Neudecker:<br /> Easiest way for me is a timing light. They can also miss fire from a lean condition. A sticking needle can also give some of these symptoms also. You could well be right about electrical on the three cylinders. Normally they will drop a cylinder when the CDI goes but can be intermittent. If the timing light shows fire to be correct while acting up, then you are back to the fuel systom.

 

[carmron2005]

Re: YAMAHA 40 INTERMITTANT MISFIRE PLEASE HELP!!!!!!!!!!!!!!!!!!!!

If in fact I am losing fire on a cylinder and I narrow it down to which one, what would the cure be? A new cdi box or possibly an igniter? How does an igniter work? Is this a type of hall-effect switch?

 

[Ray Neudecker]

Re: YAMAHA 40 INTERMITTANT MISFIRE PLEASE HELP!!!!!!!!!!!!!!!!!!!!

If it is the CDI, you will have to replace it. Sealed unit. Other tests should be done first to insure it is at fault. On most Yamahas this is such a low failure item, you almost automaticly go to fuel. Even the 3 cylinders are not a high failure item, just happens enough to make you aware of it as a possibility.