merc 650 electrical problems

I have been having electrical problems..... It's a '75 merc 650. I also have a '73 merc 650 with no electrical problems.

Background: The motor was missing badly the other day......I put a new rectifier on because it never was charging since I got it about a month ago. It charges good now. I also cleaned the rotor and distributor posts and tightened the ground strap on the distributor which was loose. Took it out for about a 2 mile run and it ran fine. I went to load it on the trailer and it bogged. I took it back out and after a little coaxing it ran fine wide open with no missing. Put it on the trailer and it bogged again. I tried to use it this morning and never got it cranked. I had no spark on any cylinders. I changed the coil with my other 650's coil and no spark. I put the other 650's switch box on it and immediately got spark. O.k., I thought, I've at least found the problem and got it fixed. I took it out again and it ran fine for about a mile or two, then started missing and I slacked off the throttle and idled. When I tried to plane it out it bogged and such. I finally got it on plane and it ran o.k. with a little missing. Less missing WOT. After cleaning out my duckblind for about an hour or so I decided to return home. It ran great for about 3/4 mile and then back to missing again. And it was surging a little at times. Definitely a cylinder losing/gaining spark. At this point, I have no idea what could be wrong. The coil and switchbox that's on the motor now worked fine on my other 650.

Question: Any ideas as to what the problem could be? I don't fully understand this system. Is the stator under the flywheel for charging only? IS the ignition run only off the battery, and the stator/rectifier keeps the battery charged?

My next step is to swap the distributor and plugwires from my good 650 to this one and see if therein lies the problem. I have a simple meter but no DVA meter and wouldn't know how to use it if I had the DVA meter. Is this a good idea?

It sounds like heat is causing something to break down. I have no idea what could be doing it. Could the problem lie in the wiring harness? Much of the harness is old.
Once again, just looking for some experience on this sort of thing.
Thanks,
JBJ

Re: merc 650 electrical problems

similar problem with my 76 Merc650, ended up replacing stator. Find out how to check it then pull flywheel and replace it, mine runs like scalded dog now, hope that fixes yours.

Re: merc 650 electrical problems

This is a battery cd ignition and only way a single cylinder can miss is:
A) Bad plug wire
B) Bad plug
C) Water leaking into cylinder from bad exhaust gaskets/plate

Re: merc 650 electrical problems

I believe it may have been hitting on just one of the 3 cylinders when I finally got to the ramp. Can anyone tell me if the stator is involved in the spark system or just the battery, switchbox, and distributor? I'm thinking the stator is only involved in the charging system. Is this correct? Also, does this motor use surface gap plugs? It has surface gaps in it.
Thanks,
JBJ

Re: merc 650 electrical problems

Hello everyone, like to say hi. This is my first post and it's gonna be long. I was just wanting to add that i to have 1975 merc 650 and have a similar if not the same problem. Lets begin, my problem began a few years ago when i got the boat out for the year, went to start it=no start. So i check for fire first thing, viola no fire so i started messing with it and couldn't figure it out. I then call my dad to ask him, we decide i should bring it over so he could ckeck it out i get there what do you know now i have fire, ran good rest of the season. Just a fluke you ask, no i don't think so. Fast forward to next year get it out first time no fire . So i start researching this thing and figured out how to test the switch box/bypass trigger in distributor, i put the jumpers on and tripped out the box and it fired. I then hook it all back up and hit the key viola it fired like it should and ran good. I could then get a restart every time i turned it off then started right back up. If i let it sit for a few minutes i'd get a no start, do a little jump on switch box bang fire up no prob. I then get a brand new o/s merc switch box and install it, fire it up umpteen times no problems. Off to the lake i go, run the lake all day not a problem go to start it up to leave what do ya know no fire again. So i then proceeded to do the old jump the (new)switch box routine and i have fire, got back without a glitch. So i have figured out that if i jump it out it will run every time(nock on wood) but it sucks that you really can't trust it. I did also try a coil on it when it wouldn't start during one of the no start situations, didn't help. Well that's my story and i'm sticking to it, although i would like to figure this out. Thanks for any input/help you can muster. Wes.

Re: merc 650 electrical problems

Thanks for that post, Wes. I know nothing about the bypass trigger in the distributor. I'm going to try switching distributors and wires and such and see if that solves my problem. Will report results. I guess I'll do a google search and find out the function of the stator.
Thanks for the help fastbullet and Hankll as well.
Later,
JBJ

Re: merc 650 electrical problems

Wesfrommo you have a bad trigger , when you jump the switchbox you are arcing the sensor(dist) internally and temporary welding contacts together. Vibration,voltage spikes and heat are what cause it to loose connection and fail again, likely runs good till you charge battery.
Jb you are correct as stator only charges the battery on this system, but if voltage drops below 10 volts pack will misfire or quit. Switchbox recieves power from battery and keyswitch. The rotor disc/sensor window in trigger housing tells pack when to fire and coil discharges back to dist. cap where rotor button sends to correct cylinder. If you have only 1 cylinder firing it is a fuel,wire,plug or mechanical(block) issue. A messed up carb can cause it to run on 1-1/2 cylinder as #2 cylinder scavanges of top & bottom carb. Considering it runs good till it heats up leads me to lean towards water intrusion. Check the tops of pistons and plugs to see if they are extremely clean like steam cleaned, if so its water in cylinder problem and it uses the surface gap plugs.

Re: merc 650 electrical problems

Thanks Fastbullet for your time.
I have cleaned both carbs. and it runs great for a while. I have checked the plugs and there's no steam cleaning for sure. Matter of fact, they're a little dirtier than I expect. I am getting good charge and voltage on my battery according to my cheapo meter. I'm going to change the distributor/wires and see what happens, along with the plugs from my other motor. If that doesn't fix it, I'm going to take off the exhaust cover and see if the water jackets are cracked/broken like my other motor and see if there is water intrusion occuring like you said. I saw a lot of white milky gunk on my old motor's plugs when it was having water intrusing into the cylinder but this one either isn't as bad or isn't happening at all. I'm sure thinking about an electrical problem but the running perfect for a while and then suddenly NOT running well has me thinking water intrusion as well. It will actually kind of stragten out and get better if I back off WOT sometimes, or go farther without practically quitting if I only run about 3/4 throttle. I hope it's not water jackets!
thanks,
JBJennings

Re: merc 650 electrical problems

Faztbullet, i don't think or i should say not sure if it's a bad trigger because (i kinda left out this detail) in my original post was i'm unhooking all the distributor wires from the switch box before i do anything. Then i take a jumper wire from wht/blk across to blk then a jumper wire from blue and touch to ground and it fires the box, I then hook up the dist. wires and it will start. So i believe that i'm taking the trigger out of the equation but i could be wrong. Thaanks again
Wes.