Poor Mid-range Power

[Barkin Buddy]

This is no doubt the place for answers. I look forward to your help. I have a 1989 Mariner 115 hp, 2-stroke, 4-cyl. that is slow to accelerate through mid-range. It struggles for a quarter mile before it finally kicks in and reaches top speed. If I have others in the boat with me then it might not even get up top speed. The fuel lines have been replaced, carbs are clean, compression is at or near 120 on all 4. Spark and fuel are there. The 3[SUP]rd[/SUP] sparkplug down is always wet though. The others always look good. I swapped coil numbers 3 and 4 as well as carbs 3 and 4 and sparkplug no. 3 is still wet. Might this be reed valves? Anything else? Will a leakdown test reveal bad reeds?

 

[racerone]

Cylinder sleeve out of position ?

 

[Barkin Buddy]

Now there's one I didn't think about. I hope its not a slipped sleeve. If it is then is this a reasonable fix for a mechanic? I'll do the leak down and try to investigate the slipped sleeve the best I can. Is there a good way to check the sleeve without significant work on my end?

 

[racerone]

Does spark jump a gap of 7/16" on all 4 leads, yes or no?-----Sounds like this motor is running on 3 of 4 cylinders.-----Is oil injection in service or bypassed ?-----Waterpump impeller replaced ?-----Fuel pump repair kit might be a good idea.

 

[Barkin Buddy]

You're right, it's just running on 3 cylinders. My spark results are from using an inline spark/ignition tester. How do I do a 7/16" spark test? Bend the side electrode out away from the center one and ground it to the block? I can see that if the pump isn't producing full pressure then it wouldn't feed all carbs equally. However, this plug is wet after every check so it is getting fuel. It pees a strong stream. I'm trying to wrap my head around the water pump thought? Sorry, I'm not a mechanic but find engines fascinating.

 

[Barkin Buddy]

Forgot to reply...the oil injection is still in service.

 

[racerone]

Water pump impellers are to be replaced about every 5 years or so on that motor.----It simply amazes me at how many folks fail to do so or do not understand why.-----Put 2 pieces of wire on a piece of cardboard / wood.---Even speaker wire will do.----Gap of 7/16" between them.----One end stuck into the plug boot and other end clipped to the motor for ground.-----Crank motor and observe.

 

[Barkin Buddy]

I know the impellers were replaced right before I bought it 3 years ago. Was expecting to replace them next winter. I'll try your 7/16 test hopefully this coming weekend.

 

[Barkin Buddy]

Ok, it has great 7/16 spark. I noticed for the first time a leak at what I think may be an intake gasket on the side of the engine. Small bubbles of fuel and a slight whisper of an air leak while the engine is running. The leak is about 3/4" along the gasket. I'm betting that this is the problem? What could cause this other than age that I might need to look for? I don't believe it is overheating.

 

[Barkin Buddy]

Problem solved. I got too busy and turned it over to a mechanic. Basically there were too many fuel leaks. One was at an intake gasket, another on a fuel line connection and also there was a small hole in the pump diaphragm. Runs better than it ever has.