Help on mye Merc 75 4-stroke -power loss

[Mer02]

It happened suddenly. I can't get any RPM (just a little), when i'm going forward or backwards. But when the throttle is in neutral, I can reach much higher RPM, but it stops when running at neutral. Somebody help me? Maybe its water in gas, but I have a filter. And I exhanged the spark plugs. And tried with clean fuel (exterior tank).

Sorry for my english. Im norwegian.

 

[JB]

Re: Help on mye Merc 75 4-stroke -power loss

Howdy, Mer02.

Welcome to iboats.

Sounds to me like you are losing power in one or more cylinders. Possible causes are many, but simplest to identify are spark and fuel.

 

[Mer02]

Re: Help on mye Merc 75 4-stroke -power loss

I've tried new spartplugs, and new fuel. But I suspect the carb or water in motor maybe. But dont now how to repair this.

 

[jmburock]

Re: Help on mye Merc 75 4-stroke -power loss

You need to pull out each spark plug and check for a strong spark individually. Don't get zapped, it helps to buy the $10 spark plug tester from an auto supply store. If the problem is in the ignition system, new spark plugs won't make a difference. If any of your spark plugs were bright and clean before you exchanged them, this would indicate water in the cylinder. Beyond these issues, sounds like a carb rebuild might be in order. ?how long has it been since the carbs were rebuilt (cleaning with spray does nothing)...

 

[Mer02]

Re: Help on mye Merc 75 4-stroke -power loss

It can sounds like the motor is running on 3 cylinders. Maybe thats why it stops at low rps. But I can reach high rpm when the motor is at full idle inn position neutral...

 

[Mer02]

Re: Help on mye Merc 75 4-stroke -power loss

Maybe this can help you to come with an solution?

While the enginge was running, i pulled out the spark plugs. One by one. The engine was killed by sparkplug nr 1 and 4. But not the two in the middle (Who goes to the same coil by the way)...

And when i screwed out the sparkplugs, nr 1 and 4 was very dark with dust who could remind me of some exhaust thing or something. But my new sparkplugs at nr 2 and 3, was clean. They havent had connection. There were only oil on these...

Somebody??

 

[rickdb1boat]

Re: Help on mye Merc 75 4-stroke -power loss

Sounds like # 2 & 3 are getting no spark. Make sure they have no spark by checking with the spark tester or timing light hooked to the wires.. I would replace the coil if this is the case..