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92 Mercury Classic 40hp Issues

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fishak

New member
I recently got a 92 mercury classic 40hp 2 stoke outboard. I went to change the spark plugs because the previous owner says they foul out and he changes them a couple times a year. I brought in an old plug to the mercury shop when I got my new ones, but they said they weren't the right plugs and gave me the correct ones. I checked the manual and they did give me the right plugs, however after I installed them the outboard wouldn't start. I put the old plugs back in and it started up. Could that be a weak spark issue? Not sure why the incorrect spark plugs start over the recommended plugs. Any input would be great.

Also, I have been having some issues like it dying under load at low throttle and dying at idle after idling for 30 seconds or so. It seems to run decent out of the water with the garden hose attached. I did some research and am thinking I need to do a carb rebuild. It also seems a little sluggish. This is my first boat so I have nothing to compare it to. I reach about 19-22mph at full throttle, does that sound about right? Motor is on a 17' welded aluminum skiff. If anybody has any other suggestions that would be great. Thank you.​
 
If the 'recommended' plugs are Q plugs(resistor), and the plugs that run are non Q designation(non resistor) you probably have a weak spark problem. My johnson had the same problem.
 
Sorry its been a while. Haven't had as much time as I would like to be on the water this summer and figuring out this problem. Anyways...While I was diagnosing and trying to figure out the idle issues the stator went out. So i replaced the stator, put in new spark plugs, took apart and cleaned the carbs (looked brand new), and checked compression which was even in all cylinders. After all of that I am still having tough starting issues and it will not stay running at low idle while in gear. Once it dies it becomes more and more of a pain to get started again. (example: get to fishing spot and shut off the engine for 30 minutes or so and when its time to start the engine again it takes forever to start. As soon as you put it in gear it dies unless you go from neutral to forward super fast and even then it will die 3/5 times) It runs smooth and great at WOT. Not sure where to go from here. Fuel pump/fuel filter?
 
Carb idle adjustments are way off. You need an experienced mechanic to adjust it properly, then it will run fine.

Jeff
 
fastjeff said:
Carb idle adjustments are way off. You need an experienced mechanic to adjust it properly, then it will run fine.

Jeff
Click to expand...

Hmm they were (out of water with the garden hose). Should it be done under load in a garbage can of water instead? It runs fine on the garden hose in the driveway, which is weird. Also the primer bulb coming off the fuel tank will get firm and stay firm, but sometimes as its about firm it gets soft again and takes a few pumps to get firm again.
 
The primer bulb will gradually get softer as the motor runs.

The best idle adjustment is achieved, motor warmed up, in gear. I tie the boat to a dock (on leave it on the trailer), and dial in best idle. Once that's achieved, I back the idle mixture screws OUT (CCW) about a 1/4 to 1/2 a turn.

Jeff

PS: Running ina garbage can can trick you do to excessive temperature (trapped water) and smoke (unless your area is well ventilated).
 
All motors run " great " on a hose.----It just is not the same as running in the water. Carburetor adjustments must be made in the water with the motor in gear !!
 
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