1985 TOP rectifier issue?!?!

[Ksanthony]

I have been working on a 1985 Mercury 115 inline six for a few months now. I ran through all the test I could find. compression 125 with less then 10% tolerance, rebuilt the carbs, fuel pump, changed fuel lines, cleaned out and replaced fuel, spark plus looked new, wires looked new. I have spark on all six, spark crosses 3/8 gap. I got it cheap because the guy couldn't get it to run. Sad for him in only turned out to be the kill switch. Someone has already removed the mercury switch, and the idle stabilizer, black box. I have the set the timing to spec, removing the plugs and fuel and just using the cranking so I retarded it back like the manual says. Runs good on muffs, not so much in water. Hard to start, idle seems week or dies soon as I engage gear unless I quickly give it throttle. The boat will not get on plan, week hole shot, the Tach does not work currently, its mounted on a 1985 ebbtide prop is good. Question for you guys, sense I wont be back to the boat for a few days, while looking up trouble shooting on the CDI website I found two things, one if the rectifier is bad it will effect your tach, looking at the wire diagrams I can see the signal wire is sent from it. Two there is the engine wont get over 3000 RPM the first option is to remove the yellow wires from the rectifier and try again. if works now replace rectifier. I cant get my head around how that could cause the problem. Help!

 

[Chris1956]

Rectifiers can weaken spark, but you said your spark was good. Anyway, remove the rectifier and insulate the two wires. That will eliminate it.

You should set the idle pickup timing and max spark advance while cranking the motor, spark plug 2-6 removed and installed in their wires and grounded to the block. So when the carbs are still closed, but ready to open, set the timing to 0-9* ATDC.

Now advance the throttle all the way and set max spark advance to 21* BTDC. Set the carbs idle mixture screws 1-1/2 turns open, and dunk her in the water for final mixture adjustment, in gear, warm motor, idle speed. You will want to richen the top carb 1/8 turn and test for acceleration. Repeat with mid carb and then bottom carb, testing acceleration after each adjustment.

 

[Ksanthony]

Where to start, ordered a new rectifier. Starter gear stripped out so over nighted one of them. Replaced the rectifier and rebuilt the starter. She fired right up on muffs. Decided to check my timing one last time. The manual says 4-6BTDC for initial pickup. That didn’t work out so put it back to around 5 ATDC. I left my son for five minutes and he reved the engine on muffs. Sounded good from the other side of the house. Shut it off and took it to the water. Ran the same couldn’t get above 3000 rpms. I disconnected the yellow wires in the rectifier and she opens up excellent. Top speed around 46mph. My thoughts are thank god that nothing major happened but it spun too fast and shorted out the new rectifier. I’ll order a new one and replace and not let my son alone.

 

[Chris1956]

You should recheck the idle pickup timing specs in your service manual, for your '85 engine. The older distributor models ('79 and older), used a 4-6* BTDC idle pickup timing spec.

Your motor should be a 6 coil ADI ignition, which used the 0-9* ATDC idle pickup timing spec. Max spark advance for both is 21* BTDC.

If your service manual is Clymer or Seloc, a mistake like that is almost expected....

Make sure the rectifier connections are clean and tight. If one of the DC leads is not well connected or intermittent, she will blow instantly. Also remember the casing of the rectifier must be well grounded. Your motor had grounding straps to connect the cowling and cowling support to ground. You might check them.

 

[Ksanthony]

I am going over all this with my son, it was a project boat for him he is 15... needless to say I checked those grounds on the cowling, they were off he didn't think about reconnecting them. I am not sure on the publisher of my manual I downloaded from 911manuals. the seloc online I have access to from work and it does not mention the specific range. 0-9 ATDC is a little wide, I set it at 5 but think I could idle a little better do you think it would be worth adjusting? I'm mostly an inboard diesel this is my first outboard.

 

[Chris1956]

I am not sure why the Mercury Idle pickup spec is so wide. 5* ATDC sounds as good as any other in the range.

Recifiers consist of 4 diodes wired into a bridge. They are to be connected, with 2 leads for the stator (AC voltage), one lead to battery positive and one lead to battery negative, which is ground. Mercury grounds one of the diode leads to it's casing. If any of the DC leads is not connected well, the rectifier will be damaged.

Also, the starter is insulated from the powerhead, and relies on a dedicated ground to power it.

 

[chuck_boulos@yahoo.com]

I went thru off this this years ago on my Merc 90 TOP. Always ran great on the muffs. But as soon as I put her in the water it just didn't have the get and and go. Finally realized that spark was jumping to the metal "wrap cover" because she ran fine when it was off. Finally insulated the inside with adhesive rubber (ice and water roofing barrier) and made sure the plug wires were insulated and routed away from ant ground. As-far-as the rectifier. Lifting the yellows shouldn't have damaged it.

 

[Chris1956]

Well, if your speak plug wires allow arcing to ground, they need to be replaced....

 

[bcbart82]

Did you come to a conclusion?

 

[Ksanthony]

Currently waiting on a new rectifier, I checked my new one and it came up bad. The boat starts, idles, and runs like a champ without it. I have verified that the mounting for the rectifier has a good ground now. So I am just waiting on the part to put it back together.

 

[bcbart82]

Hopefully you found a fix for this. Im curious to hear.