25hp Merc, no spark

[moxiedog]

Hi All,

I have a 1980 or 1981 mercury 25hp motor. Lately, it has been hard to start, and had a weak battery, so I have been pull starting it. It was becoming harder and harder to pull start. Yesterday, it took about 20 pulls to get it started, and ran fine once it started (it always ran fine once started). I stopped on a sandbar for about an hour, went to pull start it, and the rope broke. I had my buddy bring a brand new battery up to the sandbar, and we could not get it started. It turns over, but does not even attempt to start. It now has no spark to either cylinder. I tested the stator according to the merc factory manual. The black/white stator lead and engine ground had 14 ohms, right in spec. The black/yellow stator lead and engine ground showed at about 6, and spec says between 3.2 and 3.8 (on the Rx1000 setting). The ohms between the leads showed 5.45 and spec says it should be between 3.1 and 3.7. It says resistance will increase if engine is warm. The boat had been sitting in the sun (it was about 100 here today) but is that still too high? The trigger assembly checked out fine, as did the coils. Is the stator bad? Should I check wiring? Any other ideas? Thanks in advance.

 

[moxiedog]

Re: 25hp Merc, no spark

After more checking online, it appears that I am supposed to disconnect the black and yellow wire for the kill switch from the switch box. Do I just disconnect it, or do I ground it to check for spark?

 

[moxiedog]

Re: 25hp Merc, no spark

I talked to my local repair guy and he didnt think the stator was bad even though the resistance reading was high. He suspects it is the switch box. Before I order a switch box, I wanted to see what the opinion was here. What generally causes switch boxes to fail? Is there something else I should be ordering along with the switch box?

 

[moxiedog]

Re: 25hp Merc, no spark

I just tested it with the black/yellow kill wire disconnected from the switch box. No spark still. I retested everything, and came up with similar readings to those in the first post. What is the consensus here? Switch Box or Stator?

 

[moxiedog]

Re: 25hp Merc, no spark

Ok, no opinions, huh? I am ordering the switch box first. Let's hope that does the trick. I eagerly await the first person to tell me I am doing it wrong if it doesnt work.

 

[moxiedog]

Re: 25hp Merc, no spark

Ok, no opinions, huh? I am ordering the switch box first. Let's hope that does the trick. I eagerly await the first person to tell me I am doing it wrong if it doesnt work.

Switch Box didnt fix it. Ordering a stator now.

 

[Dave1027]

Re: 25hp Merc, no spark

Switch Box didnt fix it. Ordering a stator now.

You can throw parts at it or click my sig.

 

[moxiedog]

Re: 25hp Merc, no spark

I looked at page 76, as this is the switch box I have.

In step 1, I still had no spark.
In step 2, I wasnt sure how to check the cranking RPM. I don't think this is the problem, however, as I have a new battery, and have checked for spark by both pull-starting as well as the electric start.
In step 3, I cleaned the ground on the from the switchbox, the starter solenoid, the coils, and the big main ground by the starter. Am I missing any?
in step 4, I reported above that I felt my resistance was a little high on the black and yellow to ground, but it may have been an issue of the hot weather.
I have not done steps 5 or 6 yet, as I don't have a flywheel puller. Is there an easy enough way to remove the flywheel witout a puller? I will need to to replace the stator if that ends up being the problem. Thanks for your response.

 

[moxiedog]

Re: 25hp Merc, no spark

Bump

 

[pinboy122]

Re: 25hp Merc, no spark

Autozone will lend you a puller for free.thread the bolts in,tighten the puller bolt untill it pops up.if it doesn't pop,hit the puller bolt sharply with a hammer.

 

[moxiedog]

Re: 25hp Merc, no spark

got around to getting the flywheel off. Looks like the stator is melted. Here is a picture. Obviously, I will need a new stator (turns out I ordered the other stator). What causes stators to melt like this? Should I check or replace something else before I put a new stator in?

 

[moxiedog]

Re: 25hp Merc, no spark

Bump

 

[moxiedog]

Re: 25hp Merc, no spark

moving to the top

 

[Dave1027]

Re: 25hp Merc, no spark

A few things can cause it. Look for a short in the wiring or a bad battery. Did you charge the battery without disconnecting the motor's battery cables?

Edit: just saw where you said you had a weak battery. Trying to charge a dead battery with the stator output can make it overheat.

 

[moxiedog]

Re: 25hp Merc, no spark

Would that overheat the charging stator or the ignition stator? It is my ignition stator that melted. I ordered the ignition stator and will test the rectifier before I hook it all back up.

 

[moxiedog]

Re: 25hp Merc, no spark

Rectifier tested good. We will see how the new stator goes.

 

[moxiedog]

Re: 25hp Merc, no spark

new stator in, everything buttoned up. Have spark now. I now need to change my starter solenoid (separate issue) and i should be seaworthy again.