Mercury 50 HP 3 Cylinders, Acceleration Problem

Hi, i'm having a problem with my mid 80's Mercury 50 hp 3 cylinders, it doesn't want to accelerate more than 5 to 10 mph, i've replaced to stator cause there was a bad wire that was almost cut off from rubbing on the motor underneath the stator but it still does the same thing, i'm thinking the trigger or rectifier maybe bad, i've read in the forum that you can damage the rectifier if you don't disconnect the battery from the motor before charging the battery!, last year i had to recharge the battery a couple of times so i don't really know if that was the case, i'm gonna do some testing on the rectifier tommorrow and see, compression is fine, i would really appreciate any advice

thanks.

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

The recitifer only charges the battry and has nothing to do with the motor ing. system. You ned to do a compresion test then go from there checking for spark, testing coils, and testing the switchbox, and trigger. I charge my batteries hooked up all the time and it is better if the cables are disconected. I have not had any trouble in doing charging and the onboard chargers are hooked up all the time.If the cables are hooked to the motor and one hooks the charger cables reversed it will blow out the recitifier most of the time. Bad connections when runnig will also be bad. Too each his own when it comes to the subject I belive.
Oldman570

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

Hi, i did some test today and was wondering if it's normal for cylinder #3 having less spark then the other ones?, when i unplug cylinder 1 and 2...i get a good electric shock but not on 3#?...i can still see some spark between the #3 plug and the wire but seems less then the others, it looks like there's not enough current going to #3, i've tested the coil and they all give me the same ohms rating, the motor seems to only run on #1 & 2 cylinder cause when i unplug# 3 when the motor is running it doesn't change or do anything different.

any help would be appreciated

thanks.

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

The rectifier can cause ignition problems and manifests itself as being unable to get high RPM range under load. Disconnecting the rectifier is the test.
You appear to have an ignition problem. Most often the switch box but testing the stator first is a good idea.
When were the carbs last serviced. If it has been a long time or you don't know, then you should address this before doing any running.
Use a spark gap tester to check the sparks. They should be even in gap jump capability and capable of jumping about 1/2 inch. Spark plugs are often the problem regardless of how clean they look.
Of course if your compressions are no good then you are wasting your time with other tests.

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

James R said:

The rectifier can cause ignition problems and manifests itself as being unable to get high RPM range under load. Disconnecting the rectifier is the test.

Click to expand...

I did that test and the motor runs the same with the rectifier disconnected or connected!, should i try that test under load maybe?.

thanks

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

Jennysue said:

when i unplug cylinder 1 and 2...i get a good electric shock but not on 3#?...

Click to expand...

The "electric shock" test is not a recommended test here.


Get yourself an adjustable spark tester($10) at your local auto store. Spark should jump a 7/16ths air gap. Make sure to ground the other plugs when turning the motor over.

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

Hi, i'm still having the same problem after doing some test..., i've switch coil and still having intermediate fire on #3 cylinder and rough idling , when i disconnect #3 the motor doesn't stall or change anything , i've found a wire on the trigger that has been repaired and seems to be corroded and was wondering if i can switch some wires on the switchbox from the trigger to see if it would change cylinder?..., so my questions is = ... which wire to i swap?... and will it burn the switchbox by doing so?,

the motor is a 1986 50hp 3 cylinders with one switchbox.

thanks.

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

I'd to thank everyone who gave tips and advices to my problems,...i have found the problems, i've changed the stator because the wires coming out underneath were almost cut and corroded and replace the trigger also it had a bad wire corroded also but after replacing those parts it ran alittle better but still no acceleration,...i finally found the real problem with one of the carburator it was pluged up...i unhooked the gaz line coming out of the fuel pump going to the carburators and blew air into it with my compressor and i unpluged the one that was pluged up, what i did to figure out the problem was...i took a clean rag and pluged one of the carburators one at a time to see which one was pluged up...at first the top carburator when pluged with a rag the motor would stall but didn't stall when i pluged the bottom one...so after blowing air in the gaz line both carburators would stall the motor, i've learned alot about my motor these past couple of weeks and feel alot more confident about working on it myself and i also have the manual for it, i don't think the stator and trigger was a waist of money cause runs better now then before i had the problems so eventualy those parts would have fail anyways.

i wrote this so if someone has the same problems they can find my thread and maybe help them...cause i've seen threads where they had some of the same problems as i had but never post again to tell what was their problems and how they fixed it.

again thank you very much for posting in my thread
and hope i don't need to post for problems soon ,lol.

Pat C.

Re: Mercury 50 HP 3 Cylinders, Acceleration Problem

Thanks for letting us here on Iboats know the outcome on the repair of your motor. As you have stated , it should help others with the same problems you had. You also probbly saved yourself more trouble down the road, or water, by replacing the stator and trigger now as the wires beening bad.
Best of Boating,
Oldman570