Power loss 115 merc

[Madpole]

I am considering buying a boat with a 1985 - 115hp merc outboard. The engine starts and seems to run well on the hose fitting but loses power under a load.
The owner has had the carbs rebuilt and replaced one switchbox with no change. He also said the compression tested good.
He's done with spending anymore $$.
What will I need to do to this motor and how much will I need to spend to get it right? (I will have a complete repair manual and a fair mech. ability.
Any qualified help is appreciated.
Don (Madpole)

 

[Charlie61]

Re: Power loss 115 merc

I have a 1983 115hp inline 6 I have replaced stator, triger, volt reg; one switch box, rebuild carbs, rebuild water pump ,and replaced enrichment vale, oh! also replaced all 6 coils. and put new spark plugs. Some things I needed to replace other I wanted too. It sound like a new motor. I have about $850.00 total for part some new others used , and I looked all over for the best price. I started it today after it set for over two months within 30 sec or less. have fun

 

[Chris1956]

Re: Power loss 115 merc

madpole, When you say looses power, what does that mean? Will it accelerate from idle to 2500RPM or so?

 

[CharlieB]

Re: Power loss 115 merc

Before purchasing a used motor it would be wise to run a few simple tests yourself to help gauge the general condition of the motor.

You will need a few tools, spark plug wrench, spark tester, compression tester, remote starter switch or a helper.

Remove the plugs and screw in the compression tester, attach the spark tester. Remove the rest of the plugs and ground all the remaining plug wires. Use the remote starter switch to crank the motor while watching the spark tester to see if you get a nice hot blue arc of at least 7/16 inch. Write down the compression reading.

Repeat on each cyl and plug wire.

If all cyls read within 10% each other or less, the cyl's are most probably in good shape. If all plug wires pass the spark test then if is a good indication the ignition is acceptable as well.

Any remaining problems running are often related to the fuel system, old hoses, primer, time for a fuel pump rebuild and carb cleaning/adjustment.

 

[CharlieB]

Re: Power loss 115 merc

When testing spark, you may disconnect the throttle cable and manually move the throttle lever to WOT and back. This causes the timing lever to advance the triggers, flexing the wires. A broken yet abutted wire may function yet fail when moved causing a power loss with throttling the motor.

Broken trigger wires can be repaired/replaced, or replace the trigger assy.

 

[Dave1027]

Re: Power loss 115 merc

Excellent, CharlieB. Those two posts should be a sticky.