90 Mercury 50 HP won't start

[RobertMac]

The key was apparently left on last year, and now it won't start. I've replaced the switch box, regulator, rectofier, spark plugs, and batteries. It has a quick silver throttle. It turns over, but still won't fire. Help!

 

[JB]

Re: 90 Mercury 50 HP won't start

Hi, Robert.

Welcome to iboats.

Replacing parts is the most used, most expensive and least effective troubleshooting method known to man. I guess you know that now.

Go to the Engine FAQs and do "Outboard won't start". Let us know what you find.

 

[RobertMac]

Re: 90 Mercury 50 HP won't start

I looked at the FAQs prior to posting, and checked again to make sure I hadn't missed something. The postings on 50 HP Mercury not starting seem to deal with fuel issues, and I know mine's not a fuel issue; I have no firing at all. And I didn't find any issues related to leaving the key on.

 

[JB]

Re: 90 Mercury 50 HP won't start

That sounds like you did a search of previous posts on the topic, Robert. A very good idea.

"No fire" can be a bit ambiguous. Do you mean "no spark" on any cylinder?

How, exactly, do you know it not a fuel issue? What happened when you squirted fuel mix into the carbs?

 

[RobertMac]

Re: 90 Mercury 50 HP won't start

Checked all spark plugs with tester, but no spark on any cylinder.

After priming carbs with primer bulb, I sprayed WD-40 into the carbs and nothing happened.

 

[JB]

Re: 90 Mercury 50 HP won't start

WD-40 used to be an excellent starter fluid, but not any more.

It used to use propane as a propellant and was labelled "Extremely Flammable". That worked very well as a starter. There may be some of that "NOS". If you can find it hoard it.

Several years back they switched the propellant to CO2 to make it "safer to use" and changed the label to merely "Flammable". I will still burn, but does not make a good starter anymore.

Well, no matter. You have proved that there is no spark, so getting spark is the next step.

I don't know enough about Mercs to give you good advice on the ignition system. If you have a factory Service Manual it probably has some trouble isolating procedures you can use.

Maybe a Merc-spert will come along soon.

Good luck.

 

[CharlieB]

Re: 90 Mercury 50 HP won't start

Your Merc has a mag ignition, the switch grounds the black wire with a yellow trace to kill the motor. Leaving the key 'On' will only serve to run the starting battery dead, no harm done to the ignition.

Check to be sure that your safety lanyard is installed correctly, if no spark still then check the blackw/yellow wire with an ohm meter for continuity to ground, if none then you will need a DVA meter and follow the testing listed in the CDI Ignition Troubleshooting Guide to determine which component is at fault.

 

[RobertMac]

Re: 90 Mercury 50 HP won't start

Stator tested at 500ohms; replaced stator, and it now works! Thanks to JB and CharlieB for all the help.