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mercury 25 kills at half throttle

A

arkansashunter

Member
Hello,

I have a 1991 mercury 25. The switchbox went bad and i replaced it with what cdi said is the correct replacement pack.

My problem is that the motor starts and idles just fine but when i reach about half throttle it cuts out. My motor has a mechanical timing advance and if i unhook to linkage for it i can run the motor from idle through wide open no problem.

The cdi box that i bought also is the replacement part for the newer 25 hp motors that have electrical timing advance. i called and he said there is no timing advance in the box and that i had a stator problem.

What do yall think is the deal?
 
also the carb was just cleaned and the shop said they thought it was a timing clash issue as well.

So does the fact that the motor will run WOT with the timing linkage disconnected mean the stator is working properly?
 
gee...sounds like they gave you the wrong switchbox. the Electronic advance switch box on a mechanical advance motor.... I am surprised it will even work.

You can get one of these on ebay I think with no problem.

I think your original swithbox looks like the one below...my 1988 motor has this in it and I think they are the same between your 1991 year and my 1988.






140.jpg
 
racerone - I just put electric start on the motor and when i had the flywheel off i inspected all the wiring etc and its solid. So thats not the problem. Thank you tho.

Mcycle - Im thinking you may be right about the part either being defective or flat out wrong. I took the switchbox off of my 99 merc (it has the elec timing) and it did the exact same thing. When i told this to cdi they still refused to say it was the wrong box and it had no electric timing in it, yet it is the replacement for later model motors i think. Said it is possible the box may be bad but is most likely the stator.

So would the motor run fine through all speeds with the mechanical timing disconnected if the stator is bad?
 
You can put a timing light on this thing and see what is happening. I am amazed it even works if it is the wrong one. You can look up the part number they sold you and online check the serial number range it is suppose to fit. I bet you will find that your serial number is not listed.
 
I have a local guy who had a junk yard and had a 25 merc...so I was able to get that and a bunch of spare parts for not much $. I think a new Mallory or Sierra will work fine...maybe lean towards the mallory unit just a tad...although it would not surprise me if both were made by the same company.
 
okay, im just a little irritated with cdi after this. i know they make the best products but im not sure they have one for my particular model maybe. idk

Thank you.

I also have a ton of parts laying around from somebody basically giving me 2 electric start 99 mercs in perfect unscratch condition. Both however had the dreaded bad lower cylinder.... Put my powerhead on one lower section and the other one is just sitting there.
 
I just thought of this...something to consider since you mentioned that you converted your motor to now an electric start motor.

your old powerhead will accept the new parts as long as you replace all the parts. Be aware....and this might be part of your problem.... that the flywheels of the mechanical advance units might be different than the flywheels from the electronic advance motors ( I think but do not 100% know for certain). If you changed the flywheel from an electronic advanced motor you will need to change the stator and pickup and switch box to match it. I am quite sure you can't interchange any of those items individually, that is mixing old style with new style. I am not a merc mechanic but just a back room fix-it guy. You should be ok if your donor motors were mechanical advanced motors to start with. I don't know what year merc moved to electronic advance.
 
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yeah you are correct. I just took the ring gear off of the old flywheel. Had i known what i do now i would have put all the electronic timing advance stuff on my current motor, the linkages, stator, etc. If the switchbox they are sending me in replacement of the cdi still does the same thing and my stator is bad that is what i will do. Just didnt want to get away from the mechanical timing since its something i can easily adjust...
 
the electronic timing is actually better in all ways in my opinion. It has a lot better timing curve than the mechanical one. Once you set it it really does it own thing. If I had the choice I would go for the electronic one. One drawback in changing it however is making the motor into a "Frankenmerc"...one that no one else can easily work on or order parts for in the future.
 
yeah thats true.

Technically though since i put the powerhead on the other stump and then replaced the mechanical timing setup with the new stuff which includes all the brackets and pulleys, and also put the new stator, kill switch, charging coil, flywheel, and trigger (which i have all in a box lol) it would not be a "frankenmerc". Just a 25 mercury with a better block in my opinion.

This is actually something i am considering since i have the other motor right next to it to use as a guide.
 
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