74? merc 650 no fire

[basszzilla]

Hey all-been a while. Just got my hands on a 1974 (I think) merc 650 #4046174. Was told had good compression but no spark. Owner said he was told it needed a rectifier, replaced it and still no spark, now it is mine. It does have good comp, about 130 at all three. The jumper wire between the cowl and powerhead had burned/corroded through. Did I think Oh boy or what. Replaced wire, no spark. Disconected mercury switch, no spark. Everyone seems to think I need to check the stator, but no one knows how. Ran out to the marine store and got me a seloc manual (my first $30 mistake) this thing is lacking of info. I went ahead and bought a new coil off ebay becuase it was cheap ($10) but won't see it for a week. Okay, so what I need (that seloc doesn't seem to provide) is ohm readings or test methods for the stator, rectifier,coil, switch box and dist. I know this is asking alot but I'm pretty pissed that the manual although it seems to give good teardown and rebuild info has very little in testing procedures. Thanks in advance.

 

[Chris1956]

Re: 74? merc 650 no fire

Bass, Here is the troubleshooting post for distributor based ignitions. Clams had posted it, it should get you going.

MERCURY BATTERY-POWERED CDI TEST
FOR DISTRIBUTOR MODELS

This test is for the 332-2986 switchbox used from 1967-1978 on all the inlines.

This test assumes your coil is good (most all are).

DISCONNCT BATTERY

1. Turn off ignion
2. Disconnect all 3 wires on the distributor side of the switchbox.
3. Remove the HV lead from the coil to the center cap (remember it unscrews
from cap)
4. Reconnect that HV center lead to the COIL side only.
5. Position that HV lead about about 3/8" from ground (block, shrouds etc)
and find a way to hold it there.
6. Jumber the brown and white terminals on the dist. side of the switchbox
together.

RECONNECT BATTERRY

7. Check that you have +12 V at red terminal.
8. Turn on ignition and verify +12V at white terminal (on red terminal side)
9. Touch the black terminal to ground - unit should cause spark each time
you touch ground.

If that passes and it won't fire at all, suspect the trigger

 

[basszzilla]

Re: 74? merc 650 no fire

Thanks for the quick response, Maybe it's me and not my manual. A few questions.

2. Disconnect all 3 wires on the distributor side of the switchbox. My switchbox only seems to have one row of wires-

 

[basszzilla]

Re: 74? merc 650 no fire

WHOOPS Wrong button-continued from previous post

So just disconnect three wires from dist.

9. Touch the black terminal to ground - unit should cause spark each time
you touch ground. Should cuase spark at HV lead to ground or black terminal to ground.

Thanks

 

[Laddies]

Re: 74? merc 650 no fire

basszzilla, if I understand your question right the confusion is which wires to disconnect and jump. On your 3 cyl the wire colors are differant than the 4 and 6 cyl. engines, first there is no dist side of the box the wires are all on one side in a row, they should be in this order,white/black from the dist, black from te dist, blue from the dist,white from the ign switch only has 12 volts with the key is on, red from the solinoid 12 volt all the time, brown is the tach wire goes to the harness and green to the coil. The wires that you do the test with are like Chris says trigger wires from the dist. just differant colors disconnect all 3 from the box jump the white/ black to the black on the box and arc the blue to ground you should have spark each time you arc it if the box is good. I guess I should have said before all of this disconnect the mercury switch at the box at the white/black terminal and ck for spark

 

[basszzilla]

Re: 74? merc 650 no fire

Okay just to be sure. I have strategically located the dist side of the coil HV wire 3/8 of an inch from ground at powerhead, is this where I need to be looking for the spark? Or am I looking for spark at the blue wire to ground.

Another question about the stator. It appears by looking at the wiring diagram that the stators only real job it to charge the battery and supply voltage while the engine is running. Could I then assume that if the stator was bad and the battery was fully charged that I would still be able to get a good spark and the motor would run as long as the battery was up.

I know it doesn't sound like it but I am really quit mechanically and electrically inclined, I just don't want to make any costly mistakes, parts are just too damn expensive for this old motor. the first thing I did was to remove the mercury switch completly, it tested ok but I will leave it out until the motor is running.

Thanks for your time and helpd

 

[Plainsman]

Re: 74? merc 650 no fire

If your lucky, you can find a used one if that is what is bad. My new was 400, found a used one for 80.

 

[Laddies]

Re: 74? merc 650 no fire

Your engine is battery powered CD the stator only produces AC electric power that the rectifier turns into DC voltage to charge the battery. The battery furnishs the power to the ign. system that runs the system, the switch box converts the power back to AC and fires the coil, the trigger in the dist, tells the box when to fire and controls the engines timing and distibutes the spark to the cyls. If you don't have a spark gapper to install in the coil tower to ck for spark, just remove number 1 spark plug, turn the pistion to TDC and use a plug in the plug wire to ck for spark

 

[Plainsman]

Re: 74? merc 650 no fire

Thank you for correcting me Laddies.

 

[basszzilla]

Re: 74? merc 650 no fire

This would be a good place to put one of those icon thingies showing me hitting myself in the head with a hammer. I may have found my problem. I assumed that if the engine turns over the key switch and solinoid were good.

no power to the ign or start side of solinoid with key in run postion, both sides are hot in the start position.

I have continuity from the switch to the external plug and from the internal plug to solinoid.

What am I missing here?

If it turns out to just be the key switch [colour=]I AM [/colour]going to hit myself in the head with a hammer.

 

[Laddies]

Re: 74? merc 650 no fire

You must have 12 volts to the white switch box terminal for the engine to run hook a voltmeter on it and turn tne key on, no voltage in the run and start positions clean the engine plug and spread the male ends and recheck still no voltage with the key on wiggle the plug,still none its in the harness or switch. You can test it by using a jumper wire from the red terminal to the white to bypass the harness and switch

 

[basszzilla]

Re: 74? merc 650 no fire

I'm so confused I feel like a dog chasing it's tail. Okay, starting from scratch.
1. key on. red and white wire at switchbox have 12.7 VDC.
2. all dist/trigger wires disconected from switchbox
3. dist side HV wire placed next to ground
4. clamped white/black wire and black wire together disconnected from box
5. tap blue wire to ground-no spark or arc
6. bang head against wall
also tried test with white/black and black wire connected to box with jumper wire-repeat step six

FYI, I am performing this test with the flywheel off and no timing belt. I assume that all things being in good shape I could spin the distributer and get spark to the plugs. In doing a visual check for the stator I pulled the timing belt to match up with a new one. The old one is cracked really bad. Do I need to put everything back together?

 

[Laddies]

Re: 74? merc 650 no fire

With a jumper installed between the white/blk and blk and 12v.+ on the white termial ever time you arc the blue you should get a spark from the high voltage termial of the coil you don't need the dist to turn for the test

 

[basszzilla]

Re: 74? merc 650 no fire

Did as you said-no spark-now what?

 

[Laddies]

Re: 74? merc 650 no fire

The switch box is bad

 

[basszzilla]

Re: 74? merc 650 no fire

How about the coil? Is there a test for that.

 

[Laddies]

Re: 74? merc 650 no fire

It can be tested with a DVA and possibly a OHM meter, I never have luck with a OHM meter

 

[basszzilla]

Re: 74? merc 650 no fire

DVA = digital volt amp meter?

 

[Laddies]

Re: 74? merc 650 no fire

DVA= direct voltage adapter for use with a voltmeter it reads peak AC voltage in the system 120+ at your coil

 

[basszzilla]

Re: 74? merc 650 no fire

Okay, here we go again. Replaced the switch box, coil, trigger, and rotor these are all NOS parts, not used. Guess what-no spark.
I feel I am missing some small detail at this point.
I have 12 volts at the red and the white wire at switch box. I have checked continuity from coil wire to the cap through the rotor button and each terminal from the dist to the plugs. I can't rule out a defective new part but don't know how to check. I have ohmed the coil and the trigger and compared to old parts, resistance is close to the same readings from old to new. I will be happy to entertain any ideas no matter how silly they may seem, obviously I have missed something. So just jump on in here, I'm listening.