Mercury (Classic) 40 hp loses power on full throttle

[ramosacc]

Guys, I need some help! I have a 1989 Mercury 40 hp 4 cylinders, 2 strokes that run fine for about 10 minutes, then it started losing power but never shuts off. I can put it back on neutral and accelerate and will do fine but as soon I go back in gear, he doesn't have enough power.
Recent work on this engine;
Carburetors have been cleaned.
New spark plugs
New Fuel filter
New fuel pump
New gas tank and prime bulb
New prop
New water pump
Compression is 120 in all four cylinders.

Again, this thing starts pretty good and runs like new for a few minutes and then loses power in full throttle only. Thoughts?
Thank you, Rick.

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

Typically when a motor starts, idles, and runs well at full throttle for a bit, and then performance dies down it is a failing ignition component. And LOL at "classic". There are some guys on here with motors from the 30's and 40's!!

 

[ramosacc]

Re: Mercury (Classic) 40 hp loses power on full throttle

This motor actually said Classic on the side! LOL Thanks, I think i need to start looking stator and or coils?

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

This motor actually said Classic on the side! LOL Thanks, I think i need to start looking stator and or coils?

Whats the serial and model # so I can find a chart for it? Give the coils a visual inspection. Typically if the insulation is not cracked or melted they are good to go. You can check the resistance and make sure they are all equal. If one is open or OL then it is bad. Another thing to do is check the battery voltage when motor is running. Then check it when under a bit of throttle, and see what type of voltage it is throwing. If it is too high or low, then suspect stator. Not sure what else is in the ignition system of this motor without serial #.

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

Okay this motor has a trigger also. I would suspect an intermittent failure could be that as well.

 

[ramosacc]

Re: Mercury (Classic) 40 hp loses power on full throttle

Ok I just did a spark test and I found one cylinder with intermitent spark and weak. The other three are good! I read that I need I multimeter with dva function to check the coil? How I check the trigger? Thank you man!!

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

Ok I just did a spark test and I found one cylinder with intermitent spark and weak. The other three are good! I read that I need I multimeter with dva function to check the coil? How I check the trigger? Thank you man!!

No problem B. I have been through tons of ignition systems man. Just have to be patient. Now, unfortunately, unless you plan on testing other motors, a DVA tester is not always practical. They are around $100. Let me see in my Seloc if it says how to check the Trigger.

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

Aite check it out. The 4 cylinder motors, from 1976-1989 triggers can be checked as follows. ALL TRIGGER LEADS MUST BE DISCONNECTED TO TEST!! Resistance from Brown/White to Black should read 700-1000 ohms. Between white and violet trigger leads should also read 700-1000 ohms. Let me know what you get.

 

[CharlieB]

Re: Mercury (Classic) 40 hp loses power on full throttle

Build your own DVA adaptor easily and cheaply

http://forums.iboats.com/showthread.php?t=374544

When you go to test the triggers, disconnect the throttle cable and S L O W L Y move the throttle lever to WOT and back to idle as a trigger wire can be broken yet abutted, working part of the time and failing as the wires are moved.

NEVER ASSUME any electrical part is bad and replace it without PROVING THE FAULT as there is NO return on electrical parts.

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

Build your own DVA adaptor easily and cheaply

http://forums.iboats.com/showthread.php?t=374544

Sweet Charlie!!

 

[ramosacc]

Re: Mercury (Classic) 40 hp loses power on full throttle

Thank you guys! One coil was bad. I will replace and test this weekend on the water. I will let you know!!

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

Word. Simple fix brah!

 

[ramosacc]

Re: Mercury (Classic) 40 hp loses power on full throttle

Ok for anyone with the same issue. I found a bad coil first but still having weak spark on all others. I pulled the flywheel and guess what?? All the magnets were broken very badly. I found an used flywheel with magnets in perfect condition put it back and.....magic! I have plenty sparks. Took the boat out and is running better than ever! Thank you for all your reply and advise.

 

[sutor623]

Re: Mercury (Classic) 40 hp loses power on full throttle

Nice man, goes to show that pulling the flywheel when having an ignition issue is one of the first things to be done! Just be glad you dont have a motor from the 50's or 60's when flywheel prices are ASTRONOMICAL!!