115hp Merucry no power

[schadd]

I am really stumped. I have a 1987 mercury 115hp inline 6. It has no power at full throttle. All electrical tests out good. I had some fuel coming back out of the bottom two carbs when running. I assumed I had blown the reeds. Just took the power head apart and all reeds are intact. Any thoughts?

 

[achris]

Re: 115hp Merucry no power

Was the timing advancing fully? And was the high speed stator working properly?

 

[schadd]

Re: 115hp Merucry no power

I thought timing as well, so I had my local shop do a link and sync. They said the timing was right. The stator is new so I assume it is working properly. What is the odds of a new one being bad?

 

[achris]

Re: 115hp Merucry no power

.... What is the odds of a new one being bad?

It does happen. Did you test it?

On your reeds thought. Usually a faulty/broken/hanging reed will show up as spitting from the carb. Did you have any of that?

 

[schadd]

Re: 115hp Merucry no power

I did not test the high speed stator. Is that just a simple ohm test or do you need to test it at high speed? I had a little fuel comming back out of the carbs. Would the reeds be a lot of fuel or just a little? However, the reeds visually appear fine. None broken or hanging.

 

[achris]

Re: 115hp Merucry no power

I once had an engine that idled beautifully, but would not rev past about 1400 RPM, that was a high speed stator. I was lucky in that the part of the stator that failed affected both switchboxes. You may have one side of the stator failing, which will only be affecting one switchbox.... Can be a bugger to diagnose.

You need to do it with the engine running and a DVA meter. An ohms test may or may not show it. If it shows good on the ohmmeter, doesn't mean it's good running.

Chris..........

 

[schadd]

Re: 115hp Merucry no power

This whole rebuild started because of a dead switchbox for cylinders 2,4,6. Replaced it. It made the motor run great at low speeds, but now I had a high speed issue. Two boat mechanic told me I had blown the reeds. So I pulled the powerhead and opened her up. Reeds look fine. I have her open, so I am going to go ahead and rebuild the powerhead. Once I get it back together and run a link and sync, I will test the stator.

Could the stator have caused the switchbox to fail?

 

[achris]

Re: 115hp Merucry no power

This whole rebuild started because of a dead switchbox for cylinders 2,4,6. Replaced it. It made the motor run great at low speeds, but now I had a high speed issue. Two boat mechanic told me I had blown the reeds. So I pulled the powerhead and opened her up. Reeds look fine. I have her open, so I am going to go ahead and rebuild the powerhead. Once I get it back together and run a link and sync, I will test the stator.

Could the stator have caused the switchbox to fail?

If the reeds were the problem, then they would mess up the idle too.

Could the stator kill a switchbox? If the output is spikey or it has a bad ground, definitely. That's where I'd be looking....

Chris..........

 

[schadd]

Re: 115hp Merucry no power

Well, I rebuilt the power head. The pistons looked good. Honed the cylinders and replaced the rings. She is back together. New stator and trigger. It runs smooth on the muffs, but very rough in the water. When I put the throttle down it chugs and dies. It seems like a fuel problem. The fuel pump was rebuilt last fall. I had a mechanic rebuild the carbs last summer. Could this be a carb jet issue?

 

[Chris1956]

Re: 115hp Merucry no power

A lot of the younger mechanics do not know how to properly set the idle mixture. if it is set wrong the motor will die when you advance the throttle.

Hit the choke for a second, just before you hit the throttle. if this helps, the carbs are likely set too lean.

 

[schadd]

Re: 115hp Merucry no power

I am back working on this motor. I did as you suggested and hit the choke just before the throttle. It flooded and died. I have rebuilt/replaced just about everything on the top end.

Two thoughts left:

1) Could this just be bad fuel? I use a 50:1 oil mix and a stabalizer. Premium only. No ethonol.

2) Could this be a bad coil? (weak spark) The ohm test on the coils are good and consistant between each other.

 

[quantumman29]

Re: 115hp Merucry no power

hey man i have had the same problem exactly as with what your engine is having,
I have beat my head against the wall trying to figure it out,
after trying myself i hired a mercury mechanic who has been rebuilding inline sixes his whole life, 20 mins after he got to my house he diagnosed the problem as being both SWITCH BOXES ARE NO GOOD,

im waiting for the new switch boxes to arrive then i will install them,
the mechanic tested my stator and said it looked brand new,120 on all cylinders,
all three carbs are very clean,

id say this may be your problem too.

mike

 

[schadd]

Re: 115hp Merucry no power

That was the issue. The switchbox that controlled 1-3-5 was bad. This whole problem started because the switchbox for 2-4-6 had died. I was not getting any spark on 2-4-6. So I replaced it. I did not replace the other switchbox because I had spark on the other 3 cylinders. Both must have been damaged. I also replaced the rectifier and stator. I have been told that the switchbox will not go bad on its own. It is usually damaged by the rectifier. It is a really inexpensive part, so I replaced it. The stator had been replaced by a mechanic when this issue first started.

Thank you everyone for all of your input.